Messages in this thread | | | Date | Mon, 30 Oct 2023 09:33:26 +0530 | Subject | Re: [PATCH] sched/fair: Fix the decision for load balance | From | Shrikanth Hegde <> |
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On 10/27/23 10:47 PM, 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 | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 2048138ce54b..eff0316d6c7d 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -11083,8 +11083,9 @@ static int should_we_balance(struct lb_env *env) > return cpu == env->dst_cpu; > } >
There is comment above this /* Are we the first idle CPU? */ Maybe update that comment as /* Are we the first idle core */
> - if (idle_smt == env->dst_cpu) > - return true; > + /* Is there an idle CPU with busy siblings? */ nit: We can keep the comment style fixed in this function. /* 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;
code changes LGTM Reviewed-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com>
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