Messages in this thread | | | From | Vincent Guittot <> | Date | Mon, 30 Oct 2023 09:05:08 +0100 | Subject | Re: [PATCH] sched/fair: Fix the decision for load balance |
| |
On Mon, 30 Oct 2023 at 05:03, Shrikanth Hegde <sshegde@linux.vnet.ibm.com> wrote: > > > > 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 */
I was about to say the same but it's not always true. If we are at SMT level, we look for an idle CPU in the 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>
| |