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Date: Tue, 15 Dec 2020 16:33:32 +0800 From: Lai Jiangshan <jiangshanlai@...il.com> To: Peter Zijlstra <peterz@...radead.org> Cc: LKML <linux-kernel@...r.kernel.org>, Lai Jiangshan <laijs@...ux.alibaba.com>, Tejun Heo <tj@...nel.org>, Valentin Schneider <valentin.schneider@....com>, Daniel Bristot de Oliveira <bristot@...hat.com> Subject: Re: [PATCH 02/10] workqueue: use cpu_possible_mask instead of cpu_active_mask to break affinity On Tue, Dec 15, 2020 at 1:25 AM Peter Zijlstra <peterz@...radead.org> wrote: > > On Mon, Dec 14, 2020 at 11:54:49PM +0800, Lai Jiangshan wrote: > > From: Lai Jiangshan <laijs@...ux.alibaba.com> > > > > There might be other CPU online. The workers losing binding on its CPU > > should have chance to work on those later onlined CPUs. > > > > Fixes: 06249738a41a ("workqueue: Manually break affinity on hotplug") > > Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com> > > --- > > kernel/workqueue.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > > index aba71ab359dd..1f5b8385c0cf 100644 > > --- a/kernel/workqueue.c > > +++ b/kernel/workqueue.c > > @@ -4909,8 +4909,9 @@ static void unbind_workers(int cpu) > > > > raw_spin_unlock_irq(&pool->lock); > > > > + /* don't rely on the scheduler to force break affinity for us. */ > > for_each_pool_worker(worker, pool) > > - WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_active_mask) < 0); > > + WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0); > > Please explain this one.. it's not making sense. Also the Changelog > doesn't seem remotely related to the actual change. If the scheduler doesn't break affinity for us any more, I hope that we can "emulate" previous behavior when the scheduler did breaks affinity for us. The behavior is "changing the cpumask to cpu_possible_mask". And there might be some other CPUs online later while the worker is still running with the pending work items. I hope the worker can also use the later online CPUs as before. If we use cpu_active_mask here, we can't achieve this. This is what the changelog said. I don't know which wording is better, I will combine both if this reason stands. > > Afaict this is actively wrong. > > Also, can you please not Cc me parts of a series? That's bloody > annoying. Sorry about it. I was taught "once don't send the whole series to someone" and very probably I missed the conditions about it. I think in this case, I should Cc you the whole series. May I? Thanks Lai
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