Messages in this thread | | | Date | Tue, 31 Oct 2023 14:18:23 +0800 | From | Chen Yu <> | Subject | Re: [PATCH v2] sched/fair: Fix the decision for load balance |
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On 2023-10-31 at 13:59:30 +0800, Chen Yu wrote: > 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, >
I suppose you can also carry the Reviewed-by tags in V1(Shrikanth and Vincent's) as there is no code change.
Reviewed-by: Chen Yu <yu.c.chen@intel.com>
thanks, Chenyu
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