From: Thomas Gleixner <tglx@linutronix.de>
To: Christoph Hellwig <hch@infradead.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Christoph Hellwig <hch@infradead.org>,
David Runge <dave@sleepmap.de>,
linux-rt-users@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Daniel Wagner <dwagner@suse.de>
Subject: Re: [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT
Date: Tue, 27 Oct 2020 18:05:15 +0100 [thread overview]
Message-ID: <87eelj1tx0.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20201027160742.GA19073@infradead.org>
On Tue, Oct 27 2020 at 16:07, Christoph Hellwig wrote:
> On Tue, Oct 27, 2020 at 11:11:02AM +0100, Sebastian Andrzej Siewior wrote:
>> Right. I found this David Runge's log:
>
> True, ->bi_end_io instances can do a lot of things as long as they
> are hardirq safe.
>
> And in the end the IPI case isn't the super fast path anyway, as it
> means we don't use a queue per CPU.
>
> Is there a way to raise a softirq and preferably place it on a given
> CPU without our IPI dance? That should be a win-win situation for
> everyone.
Not really. Softirq pending bits are strictly per cpu and we don't have
locking or atomics to set them remotely. Even if we had that, then you'd
still need a mechanism to make sure that the remote CPU actually
processes them. So you'd still need an IPI of some sorts.
Thanks,
tglx
next prev parent reply other threads:[~2020-10-27 17:08 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-21 17:50 5.9.1-rt18: issues with Firewire card on AMD hardware David Runge
2020-10-23 11:04 ` [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT Sebastian Andrzej Siewior
2020-10-23 11:21 ` Christoph Hellwig
2020-10-23 13:52 ` Sebastian Andrzej Siewior
2020-10-27 9:26 ` Christoph Hellwig
2020-10-27 10:11 ` Sebastian Andrzej Siewior
2020-10-27 16:07 ` Christoph Hellwig
2020-10-27 17:05 ` Thomas Gleixner [this message]
2020-10-27 17:23 ` Christoph Hellwig
2020-10-27 17:59 ` Sebastian Andrzej Siewior
2020-10-27 20:58 ` Sebastian Andrzej Siewior
2020-10-28 6:56 ` Christoph Hellwig
2020-10-28 14:12 ` [PATCH 1/3] blk-mq: Don't complete on a remote CPU in force threaded mode Sebastian Andrzej Siewior
2020-10-28 14:12 ` [PATCH 2/3] blk-mq: Always complete remote completions requests in softirq Sebastian Andrzej Siewior
2020-10-28 14:12 ` [PATCH 3/3] blk-mq: Use llist_head for blk_cpu_done Sebastian Andrzej Siewior
2020-10-28 14:44 ` Christoph Hellwig
2020-10-28 14:47 ` Sebastian Andrzej Siewior
2020-10-29 13:12 ` Sebastian Andrzej Siewior
2020-10-29 14:05 ` Christoph Hellwig
2020-10-29 14:56 ` Sebastian Andrzej Siewior
2020-10-29 14:57 ` Christoph Hellwig
2020-10-29 20:03 ` Sagi Grimberg
2020-10-29 21:01 ` Sebastian Andrzej Siewior
2020-10-29 21:07 ` Sagi Grimberg
2020-10-31 10:41 ` Sebastian Andrzej Siewior
2020-10-31 15:00 ` Jens Axboe
2020-10-31 15:01 ` Jens Axboe
2020-10-31 18:09 ` Christoph Hellwig
2020-11-02 9:55 ` Sebastian Andrzej Siewior
2020-11-02 18:12 ` Christoph Hellwig
2020-11-04 19:15 ` Sagi Grimberg
2020-11-06 15:23 ` Sebastian Andrzej Siewior
2020-10-28 10:04 ` [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT Peter Zijlstra
2020-10-26 0:37 ` 5.9.1-rt18: issues with Firewire card on AMD hardware David Runge
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