| Message ID | 20180702190154.6864-1-srinivas.pandruvada@linux.intel.com |
|---|---|
| Headers | show |
| Series | ata: libahci: devslp fixes | expand |
Hi Tejan, On Mon, 2018-07-02 at 12:01 -0700, Srinivas Pandruvada wrote: > Some minor fixes to be able to correctly set devslp register > to optimize power. > > Srinivas Pandruvada (2): > ata: libahci: Correct setting of DEVSLP register > ata: libahci: Allow reconfigure of DEVSLP register > Are you applying this series? Thanks, Srinivas > drivers/ata/libahci.c | 20 ++++++++++++-------- > 1 file changed, 12 insertions(+), 8 deletions(-) > -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Jul 30, 2018 at 08:15:47AM -0700, Srinivas Pandruvada wrote: > Hi Tejan, > > On Mon, 2018-07-02 at 12:01 -0700, Srinivas Pandruvada wrote: > > Some minor fixes to be able to correctly set devslp register > > to optimize power. > > > > Srinivas Pandruvada (2): > > ata: libahci: Correct setting of DEVSLP register > > ata: libahci: Allow reconfigure of DEVSLP register > > > Are you applying this series? I was waiting for Hans's reviews. Hans, what do you think? Thanks.
Hi, On 30-07-18 17:22, Tejun Heo wrote: > On Mon, Jul 30, 2018 at 08:15:47AM -0700, Srinivas Pandruvada wrote: >> Hi Tejan, >> >> On Mon, 2018-07-02 at 12:01 -0700, Srinivas Pandruvada wrote: >>> Some minor fixes to be able to correctly set devslp register >>> to optimize power. >>> >>> Srinivas Pandruvada (2): >>> ata: libahci: Correct setting of DEVSLP register >>> ata: libahci: Allow reconfigure of DEVSLP register >>> >> Are you applying this series? > > I was waiting for Hans's reviews. Hans, what do you think? Ah I missed that this was another series. With the caveat that I do not really know that much about devslp, both patches seem sensible to me, so both are: Reviewed-by: Hans de Goede <hdegoede@redhat.com> Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Jul 30, 2018 at 05:26:45PM +0200, Hans de Goede wrote: > Hi, > > On 30-07-18 17:22, Tejun Heo wrote: > >On Mon, Jul 30, 2018 at 08:15:47AM -0700, Srinivas Pandruvada wrote: > >>Hi Tejan, > >> > >>On Mon, 2018-07-02 at 12:01 -0700, Srinivas Pandruvada wrote: > >>>Some minor fixes to be able to correctly set devslp register > >>>to optimize power. > >>> > >>>Srinivas Pandruvada (2): > >>> ata: libahci: Correct setting of DEVSLP register > >>> ata: libahci: Allow reconfigure of DEVSLP register > >>> > >>Are you applying this series? > > > >I was waiting for Hans's reviews. Hans, what do you think? > > Ah I missed that this was another series. With the caveat that > I do not really know that much about devslp, both patches > seem sensible to me, so both are: > > Reviewed-by: Hans de Goede <hdegoede@redhat.com> Applied 1-2 to libata/for-4.19. Thanks.
Srinivas, I am looking at problem on a laptop machine that suspends to S01x, but link_management is set to max_performance, because the machine is connected to a charger. Given DVLSP must be set before the laptop suspends ["""One of the requirement for modern x86 system to enter lowest power mode (SLP_S0) is SATA IP block to be off."""], the machine never reaches S01x. Does it make sense to change the target_lpm_policy at suspend (ata_port_suspend()) to min_power and bring it back to the original value on resume? Gwendal. On Mon, Jul 30, 2018 at 10:33 AM Tejun Heo <tj@kernel.org> wrote: > > On Mon, Jul 30, 2018 at 05:26:45PM +0200, Hans de Goede wrote: > > Hi, > > > > On 30-07-18 17:22, Tejun Heo wrote: > > >On Mon, Jul 30, 2018 at 08:15:47AM -0700, Srinivas Pandruvada wrote: > > >>Hi Tejan, > > >> > > >>On Mon, 2018-07-02 at 12:01 -0700, Srinivas Pandruvada wrote: > > >>>Some minor fixes to be able to correctly set devslp register > > >>>to optimize power. > > >>> > > >>>Srinivas Pandruvada (2): > > >>> ata: libahci: Correct setting of DEVSLP register > > >>> ata: libahci: Allow reconfigure of DEVSLP register > > >>> > > >>Are you applying this series? > > > > > >I was waiting for Hans's reviews. Hans, what do you think? > > > > Ah I missed that this was another series. With the caveat that > > I do not really know that much about devslp, both patches > > seem sensible to me, so both are: > > > > Reviewed-by: Hans de Goede <hdegoede@redhat.com> > > Applied 1-2 to libata/for-4.19. > > Thanks. > > -- > tejun > -- > To unsubscribe from this list: send the line "unsubscribe linux-ide" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi, On 07-03-19 21:27, Gwendal Grignou wrote: > Srinivas, > > I am looking at problem on a laptop machine that suspends to S01x, but > link_management is set to max_performance, because the machine is > connected to a charger. What is setting it to max_performance when charging? I assume chrome-os is running something in userspace to do this (like TLP, but I guess you are not using TLP) ? Have you run benchmarks with max_performance vs the default? I seriously doubt there will be a significant difference, esp. with a chrome-os style workload. > Given DVLSP must be set before the laptop suspends ["""One of the > requirement for modern x86 system to enter lowest power mode (SLP_S0) > is SATA IP block to be off."""], the machine never reaches S01x. > Does it make sense to change the target_lpm_policy at suspend > (ata_port_suspend()) to min_power and bring it back to the original > value on resume? If userspace messes with the setting, then userspace should also put it back before suspending... The upstream kernel's default behavior is to have the target level set to a fixed level independent of the charging state. Could it be this fixed level is actually max-performance ? If that is the default the kernel comes up with, that would indicate a kernel bug. Regards, Hans > > Gwendal. > > > On Mon, Jul 30, 2018 at 10:33 AM Tejun Heo <tj@kernel.org> wrote: >> >> On Mon, Jul 30, 2018 at 05:26:45PM +0200, Hans de Goede wrote: >>> Hi, >>> >>> On 30-07-18 17:22, Tejun Heo wrote: >>>> On Mon, Jul 30, 2018 at 08:15:47AM -0700, Srinivas Pandruvada wrote: >>>>> Hi Tejan, >>>>> >>>>> On Mon, 2018-07-02 at 12:01 -0700, Srinivas Pandruvada wrote: >>>>>> Some minor fixes to be able to correctly set devslp register >>>>>> to optimize power. >>>>>> >>>>>> Srinivas Pandruvada (2): >>>>>> ata: libahci: Correct setting of DEVSLP register >>>>>> ata: libahci: Allow reconfigure of DEVSLP register >>>>>> >>>>> Are you applying this series? >>>> >>>> I was waiting for Hans's reviews. Hans, what do you think? >>> >>> Ah I missed that this was another series. With the caveat that >>> I do not really know that much about devslp, both patches >>> seem sensible to me, so both are: >>> >>> Reviewed-by: Hans de Goede <hdegoede@redhat.com> >> >> Applied 1-2 to libata/for-4.19. >> >> Thanks. >> >> -- >> tejun >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-ide" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html
Hello, On Thu, Mar 7, 2019 at 12:37 PM Hans de Goede <hdegoede@redhat.com> wrote: > > Hi, > > On 07-03-19 21:27, Gwendal Grignou wrote: > > Srinivas, > > > > I am looking at problem on a laptop machine that suspends to S01x, but > > link_management is set to max_performance, because the machine is > > connected to a charger. > > What is setting it to max_performance when charging? I assume chrome-os is > running something in userspace to do this (like TLP, but I guess you are not > using TLP) ? Yes, we have a udev script that does this. > > Have you run benchmarks with max_performance vs the default? > I seriously doubt there will be a significant difference, esp. > with a chrome-os style workload. > > > Given DVLSP must be set before the laptop suspends ["""One of the > > requirement for modern x86 system to enter lowest power mode (SLP_S0) > > is SATA IP block to be off."""], the machine never reaches S01x. > > Does it make sense to change the target_lpm_policy at suspend > > (ata_port_suspend()) to min_power and bring it back to the original > > value on resume? > > If userspace messes with the setting, then userspace should also > put it back before suspending... > > The upstream kernel's default behavior is to have the target level set > to a fixed level independent of the charging state. Could it be this > fixed level is actually max-performance ? If that is the default the > kernel comes up with, that would indicate a kernel bug. Side note: max-performance indeed can be the default forced by the kernel for some (broken) SATA devices: if (dev->horkage & ATA_HORKAGE_NOLPM) { ata_dev_warn(dev, "LPM support broken, forcing max_power\n"); dev->link->ap->target_lpm_policy = ATA_LPM_MAX_POWER; } So definitely these systems won't be able to go into S0ix today. But I think the main idea that we are asking is: 1) Yes, we acknowledge that the userspace has set it max-performance. 2) However, given that the kernel already knows that: - while in suspend, there is no real value in retaining the max-performance. - On the contrary, we know system will fail to go into lower power mode because of max-suspend. 3) Does it not make sense to use this knowledge and switch to min_power when we are actually going to suspend (even if user specified max-performance), and restore max-performance on resume? Or may be there are issues that this causes, that we're not aware of? Can you please provide us some pointers? Thanks, Rajat > > Regards, > > Hans > > > > > > > Gwendal. > > > > > > On Mon, Jul 30, 2018 at 10:33 AM Tejun Heo <tj@kernel.org> wrote: > >> > >> On Mon, Jul 30, 2018 at 05:26:45PM +0200, Hans de Goede wrote: > >>> Hi, > >>> > >>> On 30-07-18 17:22, Tejun Heo wrote: > >>>> On Mon, Jul 30, 2018 at 08:15:47AM -0700, Srinivas Pandruvada wrote: > >>>>> Hi Tejan, > >>>>> > >>>>> On Mon, 2018-07-02 at 12:01 -0700, Srinivas Pandruvada wrote: > >>>>>> Some minor fixes to be able to correctly set devslp register > >>>>>> to optimize power. > >>>>>> > >>>>>> Srinivas Pandruvada (2): > >>>>>> ata: libahci: Correct setting of DEVSLP register > >>>>>> ata: libahci: Allow reconfigure of DEVSLP register > >>>>>> > >>>>> Are you applying this series? > >>>> > >>>> I was waiting for Hans's reviews. Hans, what do you think? > >>> > >>> Ah I missed that this was another series. With the caveat that > >>> I do not really know that much about devslp, both patches > >>> seem sensible to me, so both are: > >>> > >>> Reviewed-by: Hans de Goede <hdegoede@redhat.com> > >> > >> Applied 1-2 to libata/for-4.19. > >> > >> Thanks. > >> > >> -- > >> tejun > >> -- > >> To unsubscribe from this list: send the line "unsubscribe linux-ide" in > >> the body of a message to majordomo@vger.kernel.org > >> More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, 2019-03-07 at 15:07 -0800, Rajat Jain wrote: > Hello, > > On Thu, Mar 7, 2019 at 12:37 PM Hans de Goede <hdegoede@redhat.com> > wrote: > > > > Hi, > > > > On 07-03-19 21:27, Gwendal Grignou wrote: > > > Srinivas, > > > > > > I am looking at problem on a laptop machine that suspends to > > > S01x, but > > > link_management is set to max_performance, because the machine is > > > connected to a charger. > > > > What is setting it to max_performance when charging? I assume > > chrome-os is > > running something in userspace to do this (like TLP, but I guess > > you are not > > using TLP) ? > > Yes, we have a udev script that does this. > > > > > Have you run benchmarks with max_performance vs the default? > > I seriously doubt there will be a significant difference, esp. > > with a chrome-os style workload. > > > > > Given DVLSP must be set before the laptop suspends ["""One of the > > > requirement for modern x86 system to enter lowest power > > > mode (SLP_S0) > > > is SATA IP block to be off."""], the machine never reaches S01x. > > > Does it make sense to change the target_lpm_policy at suspend > > > (ata_port_suspend()) to min_power and bring it back to the > > > original > > > value on resume? > > > > If userspace messes with the setting, then userspace should also > > put it back before suspending... > > > > The upstream kernel's default behavior is to have the target level > > set > > to a fixed level independent of the charging state. Could it be > > this > > fixed level is actually max-performance ? If that is the default > > the > > kernel comes up with, that would indicate a kernel bug. > > Side note: max-performance indeed can be the default forced by the > kernel for some (broken) SATA devices: > > if (dev->horkage & ATA_HORKAGE_NOLPM) { > ata_dev_warn(dev, "LPM support broken, forcing > max_power\n"); > dev->link->ap->target_lpm_policy = ATA_LPM_MAX_POWER; > } > > So definitely these systems won't be able to go into S0ix today. > > But I think the main idea that we are asking is: > > 1) Yes, we acknowledge that the userspace has set it max-performance. > > 2) However, given that the kernel already knows that: > - while in suspend, there is no real value in retaining the > max-performance. > - On the contrary, we know system will fail to go into lower > power mode because of max-suspend. > > 3) Does it not make sense to use this knowledge and switch to > min_power when we are actually going to suspend (even if user > specified max-performance), and restore max-performance on resume? It is all about regressions. Hence we added multiple conditions for setting default to min power. It may cause issues for some SATAs, which may not recover once enters slumber or DEVSLP. There is also case where user having issues with default LPM policy hence he changed policy to max performance. We can't detect that. So it will be much safer if user space change policy to default before calling suspend. Thanks, Srinivas > > Or may be there are issues that this causes, that we're not aware of? > Can you please provide us some pointers? > > Thanks, > > Rajat > > > > > Regards, > > > > Hans > > > > > > > > > > > > Gwendal. > > > > > > > > > On Mon, Jul 30, 2018 at 10:33 AM Tejun Heo <tj@kernel.org> wrote: > > > > > > > > On Mon, Jul 30, 2018 at 05:26:45PM +0200, Hans de Goede wrote: > > > > > Hi, > > > > > > > > > > On 30-07-18 17:22, Tejun Heo wrote: > > > > > > On Mon, Jul 30, 2018 at 08:15:47AM -0700, Srinivas > > > > > > Pandruvada wrote: > > > > > > > Hi Tejan, > > > > > > > > > > > > > > On Mon, 2018-07-02 at 12:01 -0700, Srinivas Pandruvada > > > > > > > wrote: > > > > > > > > Some minor fixes to be able to correctly set devslp > > > > > > > > register > > > > > > > > to optimize power. > > > > > > > > > > > > > > > > Srinivas Pandruvada (2): > > > > > > > > ata: libahci: Correct setting of DEVSLP register > > > > > > > > ata: libahci: Allow reconfigure of DEVSLP register > > > > > > > > > > > > > > > > > > > > > > Are you applying this series? > > > > > > > > > > > > I was waiting for Hans's reviews. Hans, what do you think? > > > > > > > > > > Ah I missed that this was another series. With the caveat > > > > > that > > > > > I do not really know that much about devslp, both patches > > > > > seem sensible to me, so both are: > > > > > > > > > > Reviewed-by: Hans de Goede <hdegoede@redhat.com> > > > > > > > > Applied 1-2 to libata/for-4.19. > > > > > > > > Thanks. > > > > > > > > -- > > > > tejun > > > > -- > > > > To unsubscribe from this list: send the line "unsubscribe > > > > linux-ide" in > > > > the body of a message to majordomo@vger.kernel.org > > > > More majordomo info at > > > > http://vger.kernel.org/majordomo-info.html
Hi, On 08-03-19 01:04, Srinivas Pandruvada wrote: > On Thu, 2019-03-07 at 15:07 -0800, Rajat Jain wrote: >> Hello, >> >> On Thu, Mar 7, 2019 at 12:37 PM Hans de Goede <hdegoede@redhat.com> >> wrote: >>> >>> Hi, >>> >>> On 07-03-19 21:27, Gwendal Grignou wrote: >>>> Srinivas, >>>> >>>> I am looking at problem on a laptop machine that suspends to >>>> S01x, but >>>> link_management is set to max_performance, because the machine is >>>> connected to a charger. >>> >>> What is setting it to max_performance when charging? I assume >>> chrome-os is >>> running something in userspace to do this (like TLP, but I guess >>> you are not >>> using TLP) ? >> >> Yes, we have a udev script that does this. >> >>> >>> Have you run benchmarks with max_performance vs the default? >>> I seriously doubt there will be a significant difference, esp. >>> with a chrome-os style workload. >>> >>>> Given DVLSP must be set before the laptop suspends ["""One of the >>>> requirement for modern x86 system to enter lowest power >>>> mode (SLP_S0) >>>> is SATA IP block to be off."""], the machine never reaches S01x. >>>> Does it make sense to change the target_lpm_policy at suspend >>>> (ata_port_suspend()) to min_power and bring it back to the >>>> original >>>> value on resume? >>> >>> If userspace messes with the setting, then userspace should also >>> put it back before suspending... >>> >>> The upstream kernel's default behavior is to have the target level >>> set >>> to a fixed level independent of the charging state. Could it be >>> this >>> fixed level is actually max-performance ? If that is the default >>> the >>> kernel comes up with, that would indicate a kernel bug. >> >> Side note: max-performance indeed can be the default forced by the >> kernel for some (broken) SATA devices: >> >> if (dev->horkage & ATA_HORKAGE_NOLPM) { >> ata_dev_warn(dev, "LPM support broken, forcing >> max_power\n"); >> dev->link->ap->target_lpm_policy = ATA_LPM_MAX_POWER; >> } >> >> So definitely these systems won't be able to go into S0ix today. >> >> But I think the main idea that we are asking is: >> >> 1) Yes, we acknowledge that the userspace has set it max-performance. >> >> 2) However, given that the kernel already knows that: >> - while in suspend, there is no real value in retaining the >> max-performance. >> - On the contrary, we know system will fail to go into lower >> power mode because of max-suspend. >> >> 3) Does it not make sense to use this knowledge and switch to >> min_power when we are actually going to suspend (even if user >> specified max-performance), and restore max-performance on resume? > > It is all about regressions. Hence we added multiple conditions for > setting default to min power. > It may cause issues for some SATAs, which may not recover once enters > slumber or DEVSLP. There is also case where user having issues with > default LPM policy hence he changed policy to max performance. We can't > detect that. > So it will be much safer if user space change policy to default before > calling suspend. Right, or simply do not mess with the setting in the first place! I noticed you did not answer this part of my original reply: "Have you run benchmarks with max_performance vs the default? I seriously doubt there will be a significant difference, esp. with a chrome-os style workload." I seriously doubt the max-performance setting has a user noticeable impact on performance. So I repeat has someone actually measured this with real-world chrome-os workloads ? Regards, Hans
On Fri, Mar 8, 2019 at 12:57 AM Hans de Goede <hdegoede@redhat.com> wrote: > > Hi, > > On 08-03-19 01:04, Srinivas Pandruvada wrote: > > On Thu, 2019-03-07 at 15:07 -0800, Rajat Jain wrote: > >> Hello, > >> > >> On Thu, Mar 7, 2019 at 12:37 PM Hans de Goede <hdegoede@redhat.com> > >> wrote: > >>> > >>> Hi, > >>> > >>> On 07-03-19 21:27, Gwendal Grignou wrote: > >>>> Srinivas, > >>>> > >>>> I am looking at problem on a laptop machine that suspends to > >>>> S01x, but > >>>> link_management is set to max_performance, because the machine is > >>>> connected to a charger. > >>> > >>> What is setting it to max_performance when charging? I assume > >>> chrome-os is > >>> running something in userspace to do this (like TLP, but I guess > >>> you are not > >>> using TLP) ? > >> > >> Yes, we have a udev script that does this. > >> > >>> > >>> Have you run benchmarks with max_performance vs the default? > >>> I seriously doubt there will be a significant difference, esp. > >>> with a chrome-os style workload. > >>> > >>>> Given DVLSP must be set before the laptop suspends ["""One of the > >>>> requirement for modern x86 system to enter lowest power > >>>> mode (SLP_S0) > >>>> is SATA IP block to be off."""], the machine never reaches S01x. > >>>> Does it make sense to change the target_lpm_policy at suspend > >>>> (ata_port_suspend()) to min_power and bring it back to the > >>>> original > >>>> value on resume? > >>> > >>> If userspace messes with the setting, then userspace should also > >>> put it back before suspending... > >>> > >>> The upstream kernel's default behavior is to have the target level > >>> set > >>> to a fixed level independent of the charging state. Could it be > >>> this > >>> fixed level is actually max-performance ? If that is the default > >>> the > >>> kernel comes up with, that would indicate a kernel bug. > >> > >> Side note: max-performance indeed can be the default forced by the > >> kernel for some (broken) SATA devices: > >> > >> if (dev->horkage & ATA_HORKAGE_NOLPM) { > >> ata_dev_warn(dev, "LPM support broken, forcing > >> max_power\n"); > >> dev->link->ap->target_lpm_policy = ATA_LPM_MAX_POWER; > >> } > >> > >> So definitely these systems won't be able to go into S0ix today. > >> > >> But I think the main idea that we are asking is: > >> > >> 1) Yes, we acknowledge that the userspace has set it max-performance. > >> > >> 2) However, given that the kernel already knows that: > >> - while in suspend, there is no real value in retaining the > >> max-performance. > >> - On the contrary, we know system will fail to go into lower > >> power mode because of max-suspend. > >> > >> 3) Does it not make sense to use this knowledge and switch to > >> min_power when we are actually going to suspend (even if user > >> specified max-performance), and restore max-performance on resume? > > > > It is all about regressions. Hence we added multiple conditions for > > setting default to min power. > > It may cause issues for some SATAs, which may not recover once enters > > slumber or DEVSLP. There is also case where user having issues with > > default LPM policy hence he changed policy to max performance. We can't > > detect that. > > So it will be much safer if user space change policy to default before > > calling suspend. Now I understand, and agree. > > Right, or simply do not mess with the setting in the first place! > > I noticed you did not answer this part of my original reply: > > "Have you run benchmarks with max_performance vs the default? > I seriously doubt there will be a significant difference, esp. > with a chrome-os style workload." > > I seriously doubt the max-performance setting has a user > noticeable impact on performance. So I repeat has someone > actually measured this with real-world chrome-os workloads ? The reason we're setting it to max-performance is not really performance - but as a work around to a broken SATA device (Transcend SSD) that can't handle DEVSLP in active state (similar to what Srinivas said). Putting it to min_power while suspended was OK because it'd be in reset anyway at that time. Thanks for your explanations and help. Rajat > > Regards, > > Hans >
On Fri, Mar 8, 2019 at 11:30 AM Rajat Jain <rajatja@google.com> wrote: > > On Fri, Mar 8, 2019 at 12:57 AM Hans de Goede <hdegoede@redhat.com> wrote: > > > > Hi, > > > > On 08-03-19 01:04, Srinivas Pandruvada wrote: > > > On Thu, 2019-03-07 at 15:07 -0800, Rajat Jain wrote: > > >> Hello, > > >> > > >> On Thu, Mar 7, 2019 at 12:37 PM Hans de Goede <hdegoede@redhat.com> > > >> wrote: > > >>> > > >>> Hi, > > >>> > > >>> On 07-03-19 21:27, Gwendal Grignou wrote: > > >>>> Srinivas, > > >>>> > > >>>> I am looking at problem on a laptop machine that suspends to > > >>>> S01x, but > > >>>> link_management is set to max_performance, because the machine is > > >>>> connected to a charger. > > >>> > > >>> What is setting it to max_performance when charging? I assume > > >>> chrome-os is > > >>> running something in userspace to do this (like TLP, but I guess > > >>> you are not > > >>> using TLP) ? > > >> > > >> Yes, we have a udev script that does this. > > >> > > >>> > > >>> Have you run benchmarks with max_performance vs the default? > > >>> I seriously doubt there will be a significant difference, esp. > > >>> with a chrome-os style workload. > > >>> > > >>>> Given DVLSP must be set before the laptop suspends ["""One of the > > >>>> requirement for modern x86 system to enter lowest power > > >>>> mode (SLP_S0) > > >>>> is SATA IP block to be off."""], the machine never reaches S01x. > > >>>> Does it make sense to change the target_lpm_policy at suspend > > >>>> (ata_port_suspend()) to min_power and bring it back to the > > >>>> original > > >>>> value on resume? > > >>> > > >>> If userspace messes with the setting, then userspace should also > > >>> put it back before suspending... > > >>> > > >>> The upstream kernel's default behavior is to have the target level > > >>> set > > >>> to a fixed level independent of the charging state. Could it be > > >>> this > > >>> fixed level is actually max-performance ? If that is the default > > >>> the > > >>> kernel comes up with, that would indicate a kernel bug. > > >> > > >> Side note: max-performance indeed can be the default forced by the > > >> kernel for some (broken) SATA devices: > > >> > > >> if (dev->horkage & ATA_HORKAGE_NOLPM) { > > >> ata_dev_warn(dev, "LPM support broken, forcing > > >> max_power\n"); > > >> dev->link->ap->target_lpm_policy = ATA_LPM_MAX_POWER; > > >> } > > >> > > >> So definitely these systems won't be able to go into S0ix today. > > >> > > >> But Idrivers/ata/libata-core.c think the main idea that we are asking is: > > >> > > >> 1) Yes, we acknowledge that the userspace has set it max-performance. > > >> > > >> 2) However, given that the kernel already knows that: > > >> - while in suspend, there is no real value in retaining the > > >> max-performance. > > >> - On the contrary, we know system will fail to go into lower > > >> power mode because of max-suspend. > > >> > > >> 3) Does it not make sense to use this knowledge and switch to > > >> min_power when we are actually going to suspend (even if user > > >> specified max-performance), and restore max-performance on resume? > > > > > > It is all about regressions. Hence we added multiple conditions for > > > setting default to min power. > > > It may cause issues for some SATAs, which may not recover once enters > > > slumber or DEVSLP. There is also case where user having issues with > > > default LPM policy hence he changed policy to max performance. We can't > > > detect that. > > > So it will be much safer if user space change policy to default before > > > calling suspend. > > Now I understand, and agree. > > > > > Right, or simply do not mess with the setting in the first place! Reading the kernel code further, I understand the intent to no setting link power from user space anymore. Before 4.16, the link was set to max_performance by the kernel; we have script to set min_power, but that was done indiscriminately, and breaks devices that need max_performance. I added one similar to intel-sata-powermgmt (at https://github.com/rickysarraf/laptop-mode-tools/blob/lmt-upstream/usr/share/laptop-mode-tools/modules/intel-sata-powermgmt), but that was a mistake for kernel 4.19. For future devices, we will make sure to not use devices with horkage ATA_HORKAGE_NOLPM or that require max_performance (see http://preston4tw.blogspot.com/2015/02/transcend-mts400-ssd-power-saving.html). Thanks for your help, Gwendal. > > > > I noticed you did not answer this part of my original reply: > > > > "Have you run benchmarks with max_performance vs the default? > > I seriously doubt there will be a significant difference, esp. > > with a chrome-os style workload." > > > > I seriously doubt the max-performance setting has a user > > noticeable impact on performance. So I repeat has someone > > actually measured this with real-world chrome-os workloads ? > > The reason we're setting it to max-performance is not really > performance - but as a work around to a broken SATA device (Transcend > SSD) that can't handle DEVSLP in active state (similar to what > Srinivas said). Putting it to min_power while suspended was OK because > it'd be in reset anyway at that time. Thanks for your explanations and > help. > > Rajat > > > > > > Regards, > > > > Hans > >