Messages in this thread Patch in this message | | | Subject | Re: [PATCH v2] NOHZ: fix nohz on cpu unplug | From | Suresh Siddha <> | Date | Wed, 04 Feb 2009 11:59:44 -0800 |
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On Tue, 2009-02-03 at 22:19 -0800, Christian Borntraeger wrote: > Am Tuesday 03 February 2009 13:28:47 schrieb Ingo Molnar: > > > > + if (!cpu_active(cpu) { > > > > > > That does not compile...I used the following: > > > if (!cpu_active(cpu)) { > > > > Could you please resubmit an updated patch? > > Suresh, > > can you send the updated patch? After all, its your work and we need your > Signed-off-by anyway. > > You can add my > Reported-by: Christian Borntraeger <borntraeger@de.ibm.com> > Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Thanks Christian for testing the fix. Ingo, appended is the updated patch. Thanks. ---
From: Suresh Siddha <suresh.b.siddha@intel.com> Subject: sched: fix nohz load balancer on cpu offline
Christian Borntraeger reports:
> After a logical cpu offline, even on a complete idle system, there > is one cpu with full ticks. It turns out that nohz.cpu_mask has the > the offlined cpu still set. > > In select_nohz_load_balancer() we check if the system is completely > idle to turn of load balancing. We compare cpu_online_map with > nohz.cpu_mask. Since cpu_online_map is updated on cpu unplug, > but nohz.cpu_mask is not, the check fails and the scheduler believes that > we need an "idle load balancer" even on a fully idle system. Since the ilb > cpu does not deactivate the timer tick this breaks NOHZ.
Fix the select_nohz_load_balancer() to not set the nohz.cpu_mask while a cpu is going offline.
Reported-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com> Tested-by: Christian Borntraeger <borntraeger@de.ibm.com> ---
diff --git a/kernel/sched.c b/kernel/sched.c index 96439a4..8a0419b 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -4026,19 +4026,24 @@ int select_nohz_load_balancer(int stop_tick) int cpu = smp_processor_id(); if (stop_tick) { - cpumask_set_cpu(cpu, nohz.cpu_mask); cpu_rq(cpu)->in_nohz_recently = 1; - /* - * If we are going offline and still the leader, give up! - */ - if (!cpu_active(cpu) && - atomic_read(&nohz.load_balancer) == cpu) { + if (!cpu_active(cpu)) { + if (atomic_read(&nohz.load_balancer) != cpu) + return 0; + + /* + * If we are going offline and still the leader, + * give up! + */ if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu) BUG(); + return 0; } + cpumask_set_cpu(cpu, nohz.cpu_mask); + /* time for ilb owner also to sleep */ if (cpumask_weight(nohz.cpu_mask) == num_online_cpus()) { if (atomic_read(&nohz.load_balancer) == cpu)
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