| Message ID | 24165.1266577276@neuling.org (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
In message <24165.1266577276@neuling.org> you wrote: > In message <1266573672.1806.70.camel@laptop> you wrote: > > On Fri, 2010-02-19 at 17:05 +1100, Michael Neuling wrote: > > > > include/linux/sched.h | 2 +- > > > > kernel/sched_fair.c | 61 +++++++++++++++++++++++++++++++++++++++++ ++ > ++-- > > > - > > > > 2 files changed, 58 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > > > index 0eef87b..42fa5c6 100644 > > > > --- a/include/linux/sched.h > > > > +++ b/include/linux/sched.h > > > > @@ -849,7 +849,7 @@ enum cpu_idle_type { > > > > #define SD_POWERSAVINGS_BALANCE 0x0100 /* Balance for power sa vings */ > > > > #define SD_SHARE_PKG_RESOURCES 0x0200 /* Domain members share cpu pkg > > > resources */ > > > > #define SD_SERIALIZE 0x0400 /* Only a single load balancing > instanc > > > e */ > > > > - > > > > +#define SD_ASYM_PACKING 0x0800 > > > > > > Would we eventually add this to SD_SIBLING_INIT in a arch specific hook, > > > or is this ok to add it generically? > > > > I'd think we'd want to keep that limited to architectures that actually > > need it. > > OK > > > > > > > > +static int update_sd_pick_busiest(struct sched_domain *sd, > > > > + struct sd_lb_stats *sds, > > > > + struct sched_group *sg, > > > > + struct sg_lb_stats *sgs) > > > > +{ > > > > + if (sgs->sum_nr_running > sgs->group_capacity) > > > > + return 1; > > > > + > > > > + if (sgs->group_imb) > > > > + return 1; > > > > + > > > > + if ((sd->flags & SD_ASYM_PACKING) && sgs->sum_nr_running) { > > > > + if (!sds->busiest) > > > > + return 1; > > > > + > > > > + if (group_first_cpu(sds->busiest) < group_first_cpu(gro up)) > > > > > > "group" => "sg" here? (I get a compile error otherwise) > > > > Oh, quite ;-) > > > > > > +static int check_asym_packing(struct sched_domain *sd, > > > > + struct sd_lb_stats *sds, > > > > + int cpu, unsigned long *imbalance) > > > > +{ > > > > + int i, cpu, busiest_cpu; > > > > > > Redefining cpu here. Looks like the cpu parameter is not really needed? > > > > Seems that way indeed, I went back and forth a few times on the actual > > implementation of this function (which started out live as a copy of > > check_power_save_busiest_group), its amazing there were only these two > > compile glitches ;-) > > :-) > > Below are the cleanups + the arch specific bits. It doesn't change your > logic at all. Obviously the PPC arch bits would need to be split into a > separate patch. > > Compiles and boots against linux-next. I have some comments on the code inline but... So when I run this, I don't get processes pulled down to the lower threads. A simple test case of running 1 CPU intensive process at SCHED_OTHER on a machine with 2 way SMT system (a POWER6 but enabling SD_ASYM_PACKING). The single processes doesn't move to lower threads as I'd hope. Also, are you sure you want to put this in generic code? It seem to be quite POWER7 specific functionality, so would be logically better in arch/powerpc. I guess some other arch *might* need it, but seems unlikely. > Mikey > --- > arch/powerpc/include/asm/cputable.h | 3 + > arch/powerpc/kernel/process.c | 7 +++ > include/linux/sched.h | 4 +- > include/linux/topology.h | 1 > kernel/sched_fair.c | 64 +++++++++++++++++++++++++++++++++ +-- > 5 files changed, 74 insertions(+), 5 deletions(-) > > Index: linux-next/arch/powerpc/include/asm/cputable.h > =================================================================== > --- linux-next.orig/arch/powerpc/include/asm/cputable.h > +++ linux-next/arch/powerpc/include/asm/cputable.h > @@ -195,6 +195,7 @@ extern const char *powerpc_base_platform > #define CPU_FTR_SAO LONG_ASM_CONST(0x0020000000000000) > #define CPU_FTR_CP_USE_DCBTZ LONG_ASM_CONST(0x0040000000000000) > #define CPU_FTR_UNALIGNED_LD_STD LONG_ASM_CONST(0x0080000000000000) > +#define CPU_FTR_ASYM_SMT4 LONG_ASM_CONST(0x0100000000000000) > > #ifndef __ASSEMBLY__ > > @@ -409,7 +410,7 @@ extern const char *powerpc_base_platform > CPU_FTR_MMCRA | CPU_FTR_SMT | \ > CPU_FTR_COHERENT_ICACHE | CPU_FTR_LOCKLESS_TLBIE | \ > CPU_FTR_PURR | CPU_FTR_SPURR | CPU_FTR_REAL_LE | \ > - CPU_FTR_DSCR | CPU_FTR_SAO) > + CPU_FTR_DSCR | CPU_FTR_SAO | CPU_FTR_ASYM_SMT4) > #define CPU_FTRS_CELL (CPU_FTR_USE_TB | CPU_FTR_LWSYNC | \ > CPU_FTR_PPCAS_ARCH_V2 | CPU_FTR_CTRL | \ > CPU_FTR_ALTIVEC_COMP | CPU_FTR_MMCRA | CPU_FTR_SMT | \ > Index: linux-next/arch/powerpc/kernel/process.c > =================================================================== > --- linux-next.orig/arch/powerpc/kernel/process.c > +++ linux-next/arch/powerpc/kernel/process.c > @@ -1265,3 +1265,10 @@ unsigned long randomize_et_dyn(unsigned > > return ret; > } > + > +int arch_sd_asym_packing(void) > +{ > + if (cpu_has_feature(CPU_FTR_ASYM_SMT4)) > + return SD_ASYM_PACKING; > + return 0; > +} > Index: linux-next/include/linux/sched.h > =================================================================== > --- linux-next.orig/include/linux/sched.h > +++ linux-next/include/linux/sched.h > @@ -849,7 +849,7 @@ enum cpu_idle_type { > #define SD_POWERSAVINGS_BALANCE 0x0100 /* Balance for power savings */ > #define SD_SHARE_PKG_RESOURCES 0x0200 /* Domain members share cpu pkg resources */ > #define SD_SERIALIZE 0x0400 /* Only a single load balancing instanc e */ > - > +#define SD_ASYM_PACKING 0x0800 /* Asymetric SMT packing */ > #define SD_PREFER_SIBLING 0x1000 /* Prefer to place tasks in a sibling d omain */ > > enum powersavings_balance_level { > @@ -881,6 +881,8 @@ static inline int sd_balance_for_package > return SD_PREFER_SIBLING; > } > > +extern int arch_sd_asym_packing(void); > + > /* > * Optimise SD flags for power savings: > * SD_BALANCE_NEWIDLE helps agressive task consolidation and power savings. > Index: linux-next/include/linux/topology.h > =================================================================== > --- linux-next.orig/include/linux/topology.h > +++ linux-next/include/linux/topology.h > @@ -102,6 +102,7 @@ int arch_update_cpu_topology(void); > | 1*SD_SHARE_PKG_RESOURCES \ > | 0*SD_SERIALIZE \ > | 0*SD_PREFER_SIBLING \ > + | arch_sd_asym_packing() \ > , \ > .last_balance = jiffies, \ > .balance_interval = 1, \ > Index: linux-next/kernel/sched_fair.c > =================================================================== > --- linux-next.orig/kernel/sched_fair.c > +++ linux-next/kernel/sched_fair.c > @@ -2086,6 +2086,7 @@ struct sd_lb_stats { > struct sched_group *this; /* Local group in this sd */ > unsigned long total_load; /* Total load of all groups in sd */ > unsigned long total_pwr; /* Total power of all groups in sd */ > + unsigned long total_nr_running; > unsigned long avg_load; /* Average load across all groups in sd */ > > /** Statistics of this group */ > @@ -2493,6 +2494,28 @@ static inline void update_sg_lb_stats(st > DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE); > } > > +static int update_sd_pick_busiest(struct sched_domain *sd, > + struct sd_lb_stats *sds, > + struct sched_group *sg, > + struct sg_lb_stats *sgs) > +{ > + if (sgs->sum_nr_running > sgs->group_capacity) > + return 1; > + > + if (sgs->group_imb) > + return 1; > + > + if ((sd->flags & SD_ASYM_PACKING) && sgs->sum_nr_running) { If we are asymetric packing... > + if (!sds->busiest) > + return 1; This just seems to be a null pointer check. From the tracing I've done, this is always true (always NULL) at this point so we return here. > + > + if (group_first_cpu(sds->busiest) < group_first_cpu(sg)) > + return 1; I'm a bit lost as to what this is for. Any clues you could provide would be appreciated. :-) Is the first cpu in this domain's busiest group before the first cpu in this group. If, so pick this as the busiest? Should this be the other way around if we want to pack the busiest to the first cpu? Mark it as the busiest if it's after (not before). Is group_first_cpu guaranteed to give us the first physical cpu (ie. thread 0 in our case) or are these virtualised at this point? I'm not seeing this hit anyway due to the null pointer check above. > + } > + > + return 0; > +} > + > /** > * update_sd_lb_stats - Update sched_group's statistics for load balancing. > * @sd: sched_domain whose statistics are to be updated. > @@ -2533,6 +2556,7 @@ static inline void update_sd_lb_stats(st > > sds->total_load += sgs.group_load; > sds->total_pwr += group->cpu_power; > + sds->total_nr_running += sgs.sum_nr_running; > > /* > * In case the child domain prefers tasks go to siblings > @@ -2547,9 +2571,8 @@ static inline void update_sd_lb_stats(st > sds->this = group; > sds->this_nr_running = sgs.sum_nr_running; > sds->this_load_per_task = sgs.sum_weighted_load; > - } else if (sgs.avg_load > sds->max_load && > - (sgs.sum_nr_running > sgs.group_capacity || > - sgs.group_imb)) { > + } else if (sgs.avg_load >= sds->max_load && > + update_sd_pick_busiest(sd, sds, group, &sgs)) { This is pretty clear. Moving stuff to the new function. > sds->max_load = sgs.avg_load; > sds->busiest = group; > sds->busiest_nr_running = sgs.sum_nr_running; > @@ -2562,6 +2585,38 @@ static inline void update_sd_lb_stats(st > } while (group != sd->groups); > } > > +int __weak sd_asym_packing_arch(void) > +{ > + return 0; > +} > + > +static int check_asym_packing(struct sched_domain *sd, > + struct sd_lb_stats *sds, > + unsigned long *imbalance) > +{ > + int i, cpu, busiest_cpu; > + > + if (!(sd->flags & SD_ASYM_PACKING)) > + return 0; > + > + if (!sds->busiest) > + return 0; > + > + i = 0; > + busiest_cpu = group_first_cpu(sds->busiest); > + for_each_cpu(cpu, sched_domain_span(sd)) { > + i++; > + if (cpu == busiest_cpu) > + break; > + } > + > + if (sds->total_nr_running > i) > + return 0; This seems to be the core of the packing logic. We make sure the busiest_cpu is not past total_nr_running. If it is we mark as imbalanced. Correct? It seems if a non zero thread/group had a pile of processes running on it and a lower thread had much less, this wouldn't fire, but I'm guessing normal load balancing would kick in that case to fix the imbalance. Any corrections to my ramblings appreciated :-) Thanks again, Mikey > + > + *imbalance = sds->max_load; > + return 1; > +} > + > /** > * fix_small_imbalance - Calculate the minor imbalance that exists > * amongst the groups of a sched_domain, during > @@ -2761,6 +2816,9 @@ find_busiest_group(struct sched_domain * > return sds.busiest; > > out_balanced: > + if (check_asym_packing(sd, &sds, imbalance)) > + return sds.busiest; > + > /* > * There is no obvious imbalance. But check if we can do some balancing > * to save power.
On Tue, 2010-02-23 at 17:08 +1100, Michael Neuling wrote: > I have some comments on the code inline but... > > So when I run this, I don't get processes pulled down to the lower > threads. A simple test case of running 1 CPU intensive process at > SCHED_OTHER on a machine with 2 way SMT system (a POWER6 but enabling > SD_ASYM_PACKING). The single processes doesn't move to lower threads as > I'd hope. > > Also, are you sure you want to put this in generic code? It seem to be > quite POWER7 specific functionality, so would be logically better in > arch/powerpc. I guess some other arch *might* need it, but seems > unlikely. Well, there are no arch hooks in the load-balancing (aside from the recent cpu_power stuff, and that really is the wrong thing to poke at for this), and I did hear some other people express interest in such a constraint. Also, load-balancing is complex enough as it is, so I prefer to keep everything in the generic code where possible, clearly things like sched_domain creation need arch topology bits, and the arch_scale* things require other arch information like cpu frequency. > > @@ -2493,6 +2494,28 @@ static inline void update_sg_lb_stats(st > > DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE); > > } > > > > +static int update_sd_pick_busiest(struct sched_domain *sd, > > + struct sd_lb_stats *sds, > > + struct sched_group *sg, > > + struct sg_lb_stats *sgs) > > +{ > > + if (sgs->sum_nr_running > sgs->group_capacity) > > + return 1; > > + > > + if (sgs->group_imb) > > + return 1; > > + > > + if ((sd->flags & SD_ASYM_PACKING) && sgs->sum_nr_running) { > > If we are asymetric packing... > > > > + if (!sds->busiest) > > + return 1; > > This just seems to be a null pointer check. > > From the tracing I've done, this is always true (always NULL) at this > point so we return here. Right, so we need to have a busiest group to take a task from, if there is no busiest yet, take this group. And in your scenario, with there being only a single task, we'd only hit this once at most, so yes it makes sense this is always NULL. > > + > > + if (group_first_cpu(sds->busiest) < group_first_cpu(sg)) > > + return 1; > > I'm a bit lost as to what this is for. Any clues you could provide > would be appreciated. :-) > > Is the first cpu in this domain's busiest group before the first cpu in > this group. If, so pick this as the busiest? > > Should this be the other way around if we want to pack the busiest to > the first cpu? Mark it as the busiest if it's after (not before). > > Is group_first_cpu guaranteed to give us the first physical cpu (ie. > thread 0 in our case) or are these virtualised at this point? > > I'm not seeing this hit anyway due to the null pointer check above. So this says, if all things being equal, and we already have a busiest, but this candidate (sg) is higher than the current (busiest) take this one. The idea is to move the highest SMT task down. > > @@ -2562,6 +2585,38 @@ static inline void update_sd_lb_stats(st > > } while (group != sd->groups); > > } > > > > +int __weak sd_asym_packing_arch(void) > > +{ > > + return 0; > > +} arch_sd_asym_packing() is what you used in topology.h > > +static int check_asym_packing(struct sched_domain *sd, > > + struct sd_lb_stats *sds, > > + unsigned long *imbalance) > > +{ > > + int i, cpu, busiest_cpu; > > + > > + if (!(sd->flags & SD_ASYM_PACKING)) > > + return 0; > > + > > + if (!sds->busiest) > > + return 0; > > + > > + i = 0; > > + busiest_cpu = group_first_cpu(sds->busiest); > > + for_each_cpu(cpu, sched_domain_span(sd)) { > > + i++; > > + if (cpu == busiest_cpu) > > + break; > > + } > > + > > + if (sds->total_nr_running > i) > > + return 0; > > This seems to be the core of the packing logic. > > We make sure the busiest_cpu is not past total_nr_running. If it is we > mark as imbalanced. Correct? > > It seems if a non zero thread/group had a pile of processes running on > it and a lower thread had much less, this wouldn't fire, but I'm > guessing normal load balancing would kick in that case to fix the > imbalance. > > Any corrections to my ramblings appreciated :-) Right, so we're concerned the scenario where there's less tasks than SMT siblings, if there's more they should all be running and the regular load-balancer will deal with it. If there's less the group will normally be balanced and we fall out and end up in check_asym_packing(). So what I tried doing with that loop is detect if there's a hole in the packing before busiest. Now that I think about it, what we need to check is if this_cpu (the removed cpu argument) is idle and less than busiest. So something like: static int check_asym_pacing(struct sched_domain *sd, struct sd_lb_stats *sds, int this_cpu, unsigned long *imbalance) { int busiest_cpu; if (!(sd->flags & SD_ASYM_PACKING)) return 0; if (!sds->busiest) return 0; busiest_cpu = group_first_cpu(sds->busiest); if (cpu_rq(this_cpu)->nr_running || this_cpu > busiest_cpu) return 0; *imbalance = (sds->max_load * sds->busiest->cpu_power) / SCHED_LOAD_SCALE; return 1; } Does that make sense? I still see two problems with this though,.. regular load-balancing only balances on the first cpu of a domain (see the *balance = 0, condition in update_sg_lb_stats()), this means that if SMT[12] are idle we'll not pull properly. Also, nohz balancing might mess this up further. We could maybe play some games with the balance decision in update_sg_lb_stats() for SD_ASYM_PACKING domains and idle == CPU_IDLE, no ideas yet on nohz though.
On Tue, 2010-02-23 at 17:24 +0100, Peter Zijlstra wrote: > > busiest_cpu = group_first_cpu(sds->busiest); > if (cpu_rq(this_cpu)->nr_running || this_cpu > busiest_cpu) > return 0; Hmm, we could change the bit in find_busiest_group() to: if (idle == CPU_IDLE && check_asym_packing()) and skip the nr_running test..
Index: linux-next/arch/powerpc/include/asm/cputable.h =================================================================== --- linux-next.orig/arch/powerpc/include/asm/cputable.h +++ linux-next/arch/powerpc/include/asm/cputable.h @@ -195,6 +195,7 @@ extern const char *powerpc_base_platform #define CPU_FTR_SAO LONG_ASM_CONST(0x0020000000000000) #define CPU_FTR_CP_USE_DCBTZ LONG_ASM_CONST(0x0040000000000000) #define CPU_FTR_UNALIGNED_LD_STD LONG_ASM_CONST(0x0080000000000000) +#define CPU_FTR_ASYM_SMT4 LONG_ASM_CONST(0x0100000000000000) #ifndef __ASSEMBLY__ @@ -409,7 +410,7 @@ extern const char *powerpc_base_platform CPU_FTR_MMCRA | CPU_FTR_SMT | \ CPU_FTR_COHERENT_ICACHE | CPU_FTR_LOCKLESS_TLBIE | \ CPU_FTR_PURR | CPU_FTR_SPURR | CPU_FTR_REAL_LE | \ - CPU_FTR_DSCR | CPU_FTR_SAO) + CPU_FTR_DSCR | CPU_FTR_SAO | CPU_FTR_ASYM_SMT4) #define CPU_FTRS_CELL (CPU_FTR_USE_TB | CPU_FTR_LWSYNC | \ CPU_FTR_PPCAS_ARCH_V2 | CPU_FTR_CTRL | \ CPU_FTR_ALTIVEC_COMP | CPU_FTR_MMCRA | CPU_FTR_SMT | \ Index: linux-next/arch/powerpc/kernel/process.c =================================================================== --- linux-next.orig/arch/powerpc/kernel/process.c +++ linux-next/arch/powerpc/kernel/process.c @@ -1265,3 +1265,10 @@ unsigned long randomize_et_dyn(unsigned return ret; } + +int arch_sd_asym_packing(void) +{ + if (cpu_has_feature(CPU_FTR_ASYM_SMT4)) + return SD_ASYM_PACKING; + return 0; +} Index: linux-next/include/linux/sched.h =================================================================== --- linux-next.orig/include/linux/sched.h +++ linux-next/include/linux/sched.h @@ -849,7 +849,7 @@ enum cpu_idle_type { #define SD_POWERSAVINGS_BALANCE 0x0100 /* Balance for power savings */ #define SD_SHARE_PKG_RESOURCES 0x0200 /* Domain members share cpu pkg resources */ #define SD_SERIALIZE 0x0400 /* Only a single load balancing instance */ - +#define SD_ASYM_PACKING 0x0800 /* Asymetric SMT packing */ #define SD_PREFER_SIBLING 0x1000 /* Prefer to place tasks in a sibling domain */ enum powersavings_balance_level { @@ -881,6 +881,8 @@ static inline int sd_balance_for_package return SD_PREFER_SIBLING; } +extern int arch_sd_asym_packing(void); + /* * Optimise SD flags for power savings: * SD_BALANCE_NEWIDLE helps agressive task consolidation and power savings. Index: linux-next/include/linux/topology.h =================================================================== --- linux-next.orig/include/linux/topology.h +++ linux-next/include/linux/topology.h @@ -102,6 +102,7 @@ int arch_update_cpu_topology(void); | 1*SD_SHARE_PKG_RESOURCES \ | 0*SD_SERIALIZE \ | 0*SD_PREFER_SIBLING \ + | arch_sd_asym_packing() \ , \ .last_balance = jiffies, \ .balance_interval = 1, \ Index: linux-next/kernel/sched_fair.c =================================================================== --- linux-next.orig/kernel/sched_fair.c +++ linux-next/kernel/sched_fair.c @@ -2086,6 +2086,7 @@ struct sd_lb_stats { struct sched_group *this; /* Local group in this sd */ unsigned long total_load; /* Total load of all groups in sd */ unsigned long total_pwr; /* Total power of all groups in sd */ + unsigned long total_nr_running; unsigned long avg_load; /* Average load across all groups in sd */ /** Statistics of this group */ @@ -2493,6 +2494,28 @@ static inline void update_sg_lb_stats(st DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE); } +static int update_sd_pick_busiest(struct sched_domain *sd, + struct sd_lb_stats *sds, + struct sched_group *sg, + struct sg_lb_stats *sgs) +{ + if (sgs->sum_nr_running > sgs->group_capacity) + return 1; + + if (sgs->group_imb) + return 1; + + if ((sd->flags & SD_ASYM_PACKING) && sgs->sum_nr_running) { + if (!sds->busiest) + return 1; + + if (group_first_cpu(sds->busiest) < group_first_cpu(sg)) + return 1; + } + + return 0; +} + /** * update_sd_lb_stats - Update sched_group's statistics for load balancing. * @sd: sched_domain whose statistics are to be updated. @@ -2533,6 +2556,7 @@ static inline void update_sd_lb_stats(st sds->total_load += sgs.group_load; sds->total_pwr += group->cpu_power; + sds->total_nr_running += sgs.sum_nr_running; /* * In case the child domain prefers tasks go to siblings @@ -2547,9 +2571,8 @@ static inline void update_sd_lb_stats(st sds->this = group; sds->this_nr_running = sgs.sum_nr_running; sds->this_load_per_task = sgs.sum_weighted_load; - } else if (sgs.avg_load > sds->max_load && - (sgs.sum_nr_running > sgs.group_capacity || - sgs.group_imb)) { + } else if (sgs.avg_load >= sds->max_load && + update_sd_pick_busiest(sd, sds, group, &sgs)) { sds->max_load = sgs.avg_load; sds->busiest = group; sds->busiest_nr_running = sgs.sum_nr_running; @@ -2562,6 +2585,38 @@ static inline void update_sd_lb_stats(st } while (group != sd->groups); } +int __weak sd_asym_packing_arch(void) +{ + return 0; +} + +static int check_asym_packing(struct sched_domain *sd, + struct sd_lb_stats *sds, + unsigned long *imbalance) +{ + int i, cpu, busiest_cpu; + + if (!(sd->flags & SD_ASYM_PACKING)) + return 0; + + if (!sds->busiest) + return 0; + + i = 0; + busiest_cpu = group_first_cpu(sds->busiest); + for_each_cpu(cpu, sched_domain_span(sd)) { + i++; + if (cpu == busiest_cpu) + break; + } + + if (sds->total_nr_running > i) + return 0; + + *imbalance = sds->max_load; + return 1; +} + /** * fix_small_imbalance - Calculate the minor imbalance that exists * amongst the groups of a sched_domain, during @@ -2761,6 +2816,9 @@ find_busiest_group(struct sched_domain * return sds.busiest; out_balanced: + if (check_asym_packing(sd, &sds, imbalance)) + return sds.busiest; + /* * There is no obvious imbalance. But check if we can do some balancing * to save power.