Messages in this thread Patch in this message | | | Date | Tue, 10 Jan 2012 22:14:55 +0530 | From | Vaidyanathan Srinivasan <> | Subject | Re: [PATCH] x86,sched: Fix sched_smt_power_savings totally broken |
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* Peter Zijlstra <a.p.zijlstra@chello.nl> [2012-01-09 12:05:56]:
> On Mon, 2012-01-09 at 19:14 -0500, Youquan Song wrote: > > Fine, I will base your suggestion to develop another patch soon. > > > > > > > @@ -3923,6 +3923,10 @@ static inline void update_sg_lb_stats(struct > > sched_domain *sd, > > SCHED_POWER_SCALE); > > if (!sgs->group_capacity) > > sgs->group_capacity = fix_small_capacity(sd, group); > > + > > + if (sched_smt_power_savings) > > + sgs->group_capacity *= 2; > > Note, this has the hard-coded assumption you only have 2 threads per > core, which while true for intel, isn't true in general. I think you > meant to write *= group->group_weight or somesuch. > > Also, you forgot to limit this to the SD_SHARE_CPUPOWER domain, you're > now doubling the capacity for all domains. > > Furthermore, have a look at the SD_PREFER_SIBLING logic and make sure > you're not fighting that.
Hi Peter,
I think I had proposed the following fix earlier. Can we revisit this now? This works, but it is not the best solution.
sched: Fix group_capacity for sched_smt_powersavings
sched_smt_powersavings for threaded systems need this fix for consolidation to sibling threads to work. Since threads have fractional capacity, group_capacity will turn out to be one always and not accommodate another task in the sibling thread.
This fix makes group_capacity a function of cpumask_weight that will enable the power saving load balancer to pack tasks among sibling threads and keep more cores idle.
Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8e42de9..77ac4ca 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4010,6 +4010,21 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu, */ if (prefer_sibling && !local_group && sds->this_has_capacity) sgs.group_capacity = min(sgs.group_capacity, 1UL); + /* + * If power savings balance is set at this domain, then + * make capacity equal to number of hardware threads to + * accommodate more tasks until capacity is reached. + */ + else if (sd->flags & SD_POWERSAVINGS_BALANCE) + sgs.group_capacity = + cpumask_weight(sched_group_cpus(sg)); + + /* + * The default group_capacity is rounded from sum of + * fractional cpu_powers of sibling hardware threads + * in order to enable fair use of available hardware + * resources. + */ if (local_group) { sds->this_load = sgs.avg_load; @@ -4432,7 +4447,8 @@ static int need_active_balance(struct sched_domain *sd, int idle, * move_tasks() will succeed. ld_moved will be true and this * active balance code will not be triggered. */ - if (sched_mc_power_savings < POWERSAVINGS_BALANCE_WAKEUP) + if (sched_mc_power_savings < POWERSAVINGS_BALANCE_WAKEUP && + sched_smt_power_savings < POWERSAVINGS_BALANCE_WAKEUP) return 0; }
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