From: peterz@infradead.org
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org, io-uring@vger.kernel.org,
Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Jens Axboe <axboe@kernel.dk>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [RFC PATCH] sched: Invoke io_wq_worker_sleeping() with enabled preemption
Date: Wed, 19 Aug 2020 15:15:07 +0200 [thread overview]
Message-ID: <20200819131507.GC2674@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200819123758.6v45rj2gvojddsnn@linutronix.de>
On Wed, Aug 19, 2020 at 02:37:58PM +0200, Sebastian Andrzej Siewior wrote:
> I don't see a significant reason why this lock should become a
> raw_spinlock_t therefore I suggest to move it after the
> tsk_is_pi_blocked() check.
> Any feedback on this vs raw_spinlock_t?
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> fs/io-wq.c | 8 ++++----
> kernel/sched/core.c | 10 +++++-----
> 2 files changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 3bbb60b97c73c..b76c0f27bd95e 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4694,18 +4694,18 @@ static inline void sched_submit_work(struct task_struct *tsk)
> * in the possible wakeup of a kworker and because wq_worker_sleeping()
> * requires it.
> */
> - if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER)) {
> + if (tsk->flags & PF_WQ_WORKER) {
> preempt_disable();
> - if (tsk->flags & PF_WQ_WORKER)
> - wq_worker_sleeping(tsk);
> - else
> - io_wq_worker_sleeping(tsk);
> + wq_worker_sleeping(tsk);
> preempt_enable_no_resched();
> }
>
> if (tsk_is_pi_blocked(tsk))
> return;
>
> + if (tsk->flags & PF_IO_WORKER)
> + io_wq_worker_sleeping(tsk);
> +
Urgh, so this adds a branch in what is normally considered a fairly hot
path.
I'm thinking that the raw_spinlock_t option would permit leaving that
single:
if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER))
branch intact?
next prev parent reply other threads:[~2020-08-19 13:26 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-19 12:37 [RFC PATCH] sched: Invoke io_wq_worker_sleeping() with enabled preemption Sebastian Andrzej Siewior
2020-08-19 13:15 ` peterz [this message]
2020-08-19 13:18 ` Jens Axboe
2020-08-19 19:44 ` [PATCH] io_wq: Make io_wqe::lock a raw_spinlock_t Sebastian Andrzej Siewior
2020-09-01 8:41 ` [PATCH v2] " Sebastian Andrzej Siewior
2020-09-01 14:17 ` Jens Axboe
2020-08-19 13:33 ` [RFC PATCH] sched: Invoke io_wq_worker_sleeping() with enabled preemption Sebastian Andrzej Siewior
2020-08-19 14:21 ` peterz
2020-08-19 19:55 ` [PATCH 1/2] sched: Bring the PF_IO_WORKER and PF_WQ_WORKER bits closer together Sebastian Andrzej Siewior
2020-08-19 20:00 ` [PATCH 2/2] sched: Cache task_struct::flags in sched_submit_work() Sebastian Andrzej Siewior
2020-08-19 20:11 ` Peter Zijlstra
2020-09-07 12:58 ` [PATCH 1/2] sched: Bring the PF_IO_WORKER and PF_WQ_WORKER bits closer together Will Deacon
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