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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 23 Jan 2018 09:42:32 -0800
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Subject: Re: [RFC PATCH 0/4] softirq: Per vector threading v3
To:     Paolo Abeni <pabeni@redhat.com>
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        Frederic Weisbecker <frederic@kernel.org>,
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On Tue, Jan 23, 2018 at 8:57 AM, Paolo Abeni <pabeni@redhat.com> wrote:
>
>> Or is it that the workqueue execution is simply not yielding for some
>> reason?
>
> It's like that.
>
> I spent little time on it, so I haven't many data point. I'll try to
> investigate the scenario later this week.

Hmm. workqueues seem to use cond_resched_rcu_qs(), which does a
cond_resched() (and a RCU quiescent note).

But I wonder if the test triggers the "lets run lots of workqueue
threads", and then the single-threaded user space just gets blown out
of the water by many kernel threads. Each thread gets its own "fair"
amount of CPU, but..

                   Linus