| Message ID | 1436213363-18419-1-git-send-email-shreyas@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Michael Ellerman |
| Headers | show |
On Tue, 2015-07-07 at 01:39 +0530, Shreyas B. Prabhu wrote: > core_idle_state is maintained for each core. It uses 0-7 bits to track > whether a thread in the core has entered fastsleep or winkle. 8th bit is > used as a lock bit. ... > This patch fixes the above race by looping on the lock bit even while > entering the idle states. > > Signed-off-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com> > Fixes: 7b54e9f213f76 'powernv/powerpc: Add winkle support for offline > cpus' The sha is wrong, it should be 77b54e9f213f. Also please don't wrap the description. I recommend creating an alias or script that does: $ git log --pretty=fixes -n 1 $commit | xclip I've fixed it up, no need to resend. cheers
On 07/07/2015 05:52 AM, Michael Ellerman wrote: > On Tue, 2015-07-07 at 01:39 +0530, Shreyas B. Prabhu wrote: >> Signed-off-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com> >> Fixes: 7b54e9f213f76 'powernv/powerpc: Add winkle support for offline >> cpus' > > The sha is wrong, it should be 77b54e9f213f. > Argh! Sorry > Also please don't wrap the description. > > I recommend creating an alias or script that does: > > $ git log --pretty=fixes -n 1 $commit | xclip > Will use this from next time. > > I've fixed it up, no need to resend. > Thanks! --Shreyas
On Mon, 2015-06-07 at 20:09:23 UTC, "Shreyas B. Prabhu" wrote: > core_idle_state is maintained for each core. It uses 0-7 bits to track > whether a thread in the core has entered fastsleep or winkle. 8th bit is > used as a lock bit. ... > Signed-off-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com> > Fixes: 7b54e9f213f76 'powernv/powerpc: Add winkle support for offline > cpus' Applied to powerpc fixes, thanks. https://git.kernel.org/cgit/linux/kernel/git/powerpc/linux.git/commit/?h=fixes&id=b32aadc1a8ed84afbe924cd2ced31cd6a2e67074 cheers
> I recommend creating an alias or script that does: > > $ git log --pretty=fixes -n 1 $commit | xclip > FWIW, having finally got around to doing this, I found I first needed the following snippet in ~/.gitconfig from https://www.kernel.org/doc/Documentation/SubmittingPatches [core] abbrev = 12 [pretty] fixes = Fixes: %h (\"%s\") Otherwise git doesn't know what the pretty format is.
On 07/09/2015 10:11 AM, Daniel Axtens wrote: >> I recommend creating an alias or script that does: >> >> $ git log --pretty=fixes -n 1 $commit | xclip >> > > FWIW, having finally got around to doing this, I found I first needed > the following snippet in ~/.gitconfig from > https://www.kernel.org/doc/Documentation/SubmittingPatches > > > [core] > abbrev = 12 > [pretty] > fixes = Fixes: %h (\"%s\") > > Otherwise git doesn't know what the pretty format is. > Right, thanks for the pointer! Thanks, Shreyas
On Thu, 2015-07-09 at 14:41 +1000, Daniel Axtens wrote: > > I recommend creating an alias or script that does: > > > > $ git log --pretty=fixes -n 1 $commit | xclip > > > > FWIW, having finally got around to doing this, I found I first needed > the following snippet in ~/.gitconfig from > https://www.kernel.org/doc/Documentation/SubmittingPatches > > > [core] > abbrev = 12 > [pretty] > fixes = Fixes: %h (\"%s\") > > Otherwise git doesn't know what the pretty format is. Oh right, yeah. Doesn't everyone have my dotfiles!? cheers
diff --git a/arch/powerpc/kernel/idle_power7.S b/arch/powerpc/kernel/idle_power7.S index ccde8f0..4d04315 100644 --- a/arch/powerpc/kernel/idle_power7.S +++ b/arch/powerpc/kernel/idle_power7.S @@ -52,6 +52,22 @@ .text /* + * Used by threads when the lock bit of core_idle_state is set. + * Threads will spin in HMT_LOW until the lock bit is cleared. + * r14 - pointer to core_idle_state + * r15 - used to load contents of core_idle_state + */ + +core_idle_lock_held: + HMT_LOW +3: lwz r15,0(r14) + andi. r15,r15,PNV_CORE_IDLE_LOCK_BIT + bne 3b + HMT_MEDIUM + lwarx r15,0,r14 + blr + +/* * Pass requested state in r3: * r3 - PNV_THREAD_NAP/SLEEP/WINKLE * @@ -150,6 +166,10 @@ power7_enter_nap_mode: ld r14,PACA_CORE_IDLE_STATE_PTR(r13) lwarx_loop1: lwarx r15,0,r14 + + andi. r9,r15,PNV_CORE_IDLE_LOCK_BIT + bnel core_idle_lock_held + andc r15,r15,r7 /* Clear thread bit */ andi. r15,r15,PNV_CORE_IDLE_THREAD_BITS @@ -294,7 +314,7 @@ lwarx_loop2: * workaround undo code or resyncing timebase or restoring context * In either case loop until the lock bit is cleared. */ - bne core_idle_lock_held + bnel core_idle_lock_held cmpwi cr2,r15,0 lbz r4,PACA_SUBCORE_SIBLING_MASK(r13) @@ -319,15 +339,6 @@ lwarx_loop2: isync b common_exit -core_idle_lock_held: - HMT_LOW -core_idle_lock_loop: - lwz r15,0(14) - andi. r9,r15,PNV_CORE_IDLE_LOCK_BIT - bne core_idle_lock_loop - HMT_MEDIUM - b lwarx_loop2 - first_thread_in_subcore: /* First thread in subcore to wakeup */ ori r15,r15,PNV_CORE_IDLE_LOCK_BIT
core_idle_state is maintained for each core. It uses 0-7 bits to track whether a thread in the core has entered fastsleep or winkle. 8th bit is used as a lock bit. The lock bit is set in these 2 scenarios- - The thread is first in subcore to wakeup from sleep/winkle. - If its the last thread in the core about to enter sleep/winkle While the lock bit is set, if any other thread in the core wakes up, it loops until the lock bit is cleared before proceeding in the wakeup path. This helps prevent race conditions w.r.t fastsleep workaround and prevents threads from switching to process context before core/subcore resources are restored. But, in the path to sleep/winkle entry, we currently don't check for lock-bit. This exposes us to following race when running with subcore on- First thread in the subcorea Another thread in the same waking up core entering sleep/winkle lwarx r15,0,r14 ori r15,r15,PNV_CORE_IDLE_LOCK_BIT stwcx. r15,0,r14 [Code to restore subcore state] lwarx r15,0,r14 [clear thread bit] stwcx. r15,0,r14 andi. r15,r15,PNV_CORE_IDLE_THREAD_BITS stw r15,0(r14) Here, after the thread entering sleep clears its thread bit in core_idle_state, the value is overwritten by the thread waking up. In such cases when the core enters fastsleep, code mistakes an idle thread as running. Because of this, the first thread waking up from fastsleep which is supposed to resync timebase skips it. So we can end up having a core with stale timebase value. This patch fixes the above race by looping on the lock bit even while entering the idle states. Signed-off-by: Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com> Fixes: 7b54e9f213f76 'powernv/powerpc: Add winkle support for offline cpus' --- This needs to go into stable 3.19+ Changes in v2: ------------- - Based on suggestion from Micheal, core_idle_lock_held changed to a function call so that the same block can be called in entry and exit path. - More detail on how this bug manifests added to commit message. arch/powerpc/kernel/idle_power7.S | 31 +++++++++++++++++++++---------- 1 file changed, 21 insertions(+), 10 deletions(-)