Messages in this thread | | | Subject | Re: [PATCH v4 1/2] sched: Add per_cpu cluster domain info and cpus_share_resources API | From | Yicong Yang <> | Date | Thu, 16 Jun 2022 16:10:51 +0800 |
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On 2022/6/15 23:43, Gautham R. Shenoy wrote: > On Wed, Jun 15, 2022 at 07:49:22PM +0530, K Prateek Nayak wrote: > > [..snip..] > >> >> - Bisecting: >> >> When we ran the tests with only Patch 1 of the series, the >> regression was visible and the numbers were worse. >> >> Clients: tip cluster Patch 1 Only >> 8 3263.81 (0.00 pct) 3086.81 (-5.42 pct) 3018.63 (-7.51 pct) >> 16 6011.19 (0.00 pct) 5360.28 (-10.82 pct) 4869.26 (-18.99 pct) >> 32 12058.31 (0.00 pct) 8769.08 (-27.27 pct) 8159.60 (-32.33 pct) >> 64 21258.21 (0.00 pct) 19021.09 (-10.52 pct) 13161.92 (-38.08 pct) >> >> We further bisected the hunks to narrow down the cause to the per CPU >> variable declarations. >> >> >>> >>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h >>> index 01259611beb9..b9bcfcf8d14d 100644 >>> --- a/kernel/sched/sched.h >>> +++ b/kernel/sched/sched.h >>> @@ -1753,7 +1753,9 @@ static inline struct sched_domain *lowest_flag_domain(int cpu, int flag) >>> DECLARE_PER_CPU(struct sched_domain __rcu *, sd_llc); >>> DECLARE_PER_CPU(int, sd_llc_size); >>> DECLARE_PER_CPU(int, sd_llc_id); >>> +DECLARE_PER_CPU(int, sd_share_id); >>> DECLARE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared); >>> +DECLARE_PER_CPU(struct sched_domain __rcu *, sd_cluster); >> >> The main reason for the regression seems to be the above declarations. > > I think you meant that the regressions are due to the DEFINE_PER_CPU() > instances from the following hunk: > >>> @@ -664,6 +664,8 @@ static void destroy_sched_domains(struct sched_domain *sd) >>> DEFINE_PER_CPU(struct sched_domain __rcu *, sd_llc); >>> DEFINE_PER_CPU(int, sd_llc_size); >>> DEFINE_PER_CPU(int, sd_llc_id); >>> +DEFINE_PER_CPU(int, sd_share_id); >>> +DEFINE_PER_CPU(struct sched_domain __rcu *, sd_cluster); >>> DEFINE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared); >>> DEFINE_PER_CPU(struct sched_domain __rcu *, sd_numa); >>> DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing); >>> > > > The System.map diff for these variables between tip vs tip + > cluster-sched-v4 on your test system looks as follows: > > 0000000000020520 D sd_asym_packing > 0000000000020528 D sd_numa > -0000000000020530 D sd_llc_shared > -0000000000020538 D sd_llc_id > -000000000002053c D sd_llc_size > -0000000000020540 D sd_llc > +0000000000020530 D sd_cluster > +0000000000020538 D sd_llc_shared
looks like below are in another cacheline (for 64B cacheline)? while previous sd_llc_id and sd_llc_shared are in the same.
> +0000000000020540 D sd_share_id > +0000000000020544 D sd_llc_id > +0000000000020548 D sd_llc_size > +0000000000020550 D sd_llc > > The allocations are in the reverse-order of the definitions. > > That perhaps explains why you no longer see the regression when you > define the sd_share_id and sd_cluster per-cpu definitions at the > beginning as indicated by the following > >> - Move the declarations of sd_share_id and sd_cluster to the top >> >> Clients: tip Patch 1 Patch 1 (Declarion on Top) >> 8 3255.69 (0.00 pct) 3018.63 (-7.28 pct) 3072.30 (-5.63 pct) >> 16 6092.67 (0.00 pct) 4869.26 (-20.08 pct) 5586.59 (-8.30 pct) >> 32 11156.56 (0.00 pct) 8159.60 (-26.86 pct) 11184.17 (0.24 pct) >> 64 21019.97 (0.00 pct) 13161.92 (-37.38 pct) 20289.70 (-3.47 pct) > > > -- > Thanks and Regards > gautham. > . >
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