Messages in this thread | | | Date | Tue, 31 Oct 2023 13:59:30 +0800 | From | Chen Yu <> | Subject | Re: [PATCH v2] sched/fair: Fix the decision for load balance |
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On 2023-10-30 at 18:29:46 +0100, Keisuke Nishimura wrote: > should_we_balance is called for the decision to do load-balancing. > When sched ticks invoke this function, only one CPU should return > true. However, in the current code, two CPUs can return true. The > following situation, where b means busy and i means idle, is an > example, because CPU 0 and CPU 2 return true. > > [0, 1] [2, 3] > b b i b > > This fix checks if there exists an idle CPU with busy sibling(s) > after looking for a CPU on an idle core. If some idle CPUs with busy > siblings are found, just the first one should do load-balancing. > > Fixes: b1bfeab9b002 ("sched/fair: Consider the idle state of the whole core for load balance") > Signed-off-by: Keisuke Nishimura <keisuke.nishimura@inria.fr> > --- > kernel/sched/fair.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 2048138ce54b..69d63fae34f4 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -11079,12 +11079,16 @@ static int should_we_balance(struct lb_env *env) > continue; > } > > - /* Are we the first idle CPU? */ > + /* > + * Are we the first idle core in a MC or higher domain
It is possible that the Cluster domain is lower than a MC. cluser domain: CPUs share the same L2 MC domain: CPUs share the same LLC
grep . domain*/{name,flags} domain0/name:CLS domain1/name:MC domain2/name:NUMA domain0/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING domain1/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_PKG_RESOURCES SD_PREFER_SIBLING domain2/flags:SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SERIALIZE SD_OVERLAP SD_NUMA
So, maybe: Are we the first idle core in a non-SMT domain or higher,
thanks, Chenyu
> + * or the first idle CPU in a SMT domain? > + */ > return cpu == env->dst_cpu; > } > > - if (idle_smt == env->dst_cpu) > - return true; > + /* Are we the first idle CPU with busy siblings? */ > + if (idle_smt != -1) > + return idle_smt == env->dst_cpu; > > /* Are we the first CPU of this group ? */ > return group_balance_cpu(sg) == env->dst_cpu; > -- > 2.34.1 >
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