From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Christoph Hellwig <hch@infradead.org>
Cc: Hannes Reinecke <hare@suse.de>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
Jens Axboe <axboe@kernel.dk>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 2/3] blk-mq: Always complete remote completions requests in softirq
Date: Mon, 25 Jan 2021 09:30:29 +0100 [thread overview]
Message-ID: <20210125083029.utnjqs2s3diqb5vx@linutronix.de> (raw)
In-Reply-To: <20210125082542.GC942655@infradead.org>
On 2021-01-25 08:25:42 [+0000], Christoph Hellwig wrote:
> On Mon, Jan 25, 2021 at 08:10:16AM +0100, Hannes Reinecke wrote:
> > I don't get this.
> > This code is about _avoiding_ having to raise a softirq if the driver
> > exports more than one hardware queue.
> > So where exactly does the remote CPU case come in here?
>
> __blk_mq_complete_request_remote is only called for the case where we
> do not completelky locally. The case that "degrades" here is where
> the device supports multiple queues, but less than the number of CPUs,
> and we bounce the completion to another CPU.
Does it really "degrade" or just use the softirq more often? The usual
case is run the softirqs in irq_exit() which is just after IPI.
Sebastian
next prev parent reply other threads:[~2021-01-26 20:13 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-23 20:10 [PATCH v3 0/3] blk-mq: Don't complete in IRQ, use llist_head Sebastian Andrzej Siewior
2021-01-23 20:10 ` [PATCH 1/3] smp: Process pending softirqs in flush_smp_call_function_from_idle() Sebastian Andrzej Siewior
2021-02-01 19:35 ` Sebastian Andrzej Siewior
2021-02-09 10:02 ` Peter Zijlstra
2021-02-09 11:35 ` Sebastian Andrzej Siewior
2021-02-10 13:53 ` [tip: sched/core] " tip-bot2 for Sebastian Andrzej Siewior
2021-02-17 13:17 ` tip-bot2 for Sebastian Andrzej Siewior
2021-01-23 20:10 ` [PATCH 2/3] blk-mq: Always complete remote completions requests in softirq Sebastian Andrzej Siewior
2021-01-25 7:10 ` Hannes Reinecke
2021-01-25 8:25 ` Christoph Hellwig
2021-01-25 8:30 ` Sebastian Andrzej Siewior [this message]
2021-01-25 8:32 ` Christoph Hellwig
2021-01-25 9:29 ` Sebastian Andrzej Siewior
2021-01-25 8:22 ` Christoph Hellwig
2021-01-25 8:49 ` Christoph Hellwig
2021-01-27 11:22 ` Daniel Wagner
2021-01-23 20:10 ` [PATCH 3/3] blk-mq: Use llist_head for blk_cpu_done Sebastian Andrzej Siewior
2021-01-25 8:30 ` Christoph Hellwig
2021-01-25 8:32 ` Sebastian Andrzej Siewior
2021-01-25 8:39 ` Christoph Hellwig
2021-01-25 9:54 ` [PATCH 3/3 v2] " Sebastian Andrzej Siewior
2021-01-25 10:14 ` Christoph Hellwig
2021-01-27 11:23 ` Daniel Wagner
2021-01-25 4:27 ` [PATCH v3 0/3] blk-mq: Don't complete in IRQ, use llist_head Jens Axboe
2021-02-10 14:43 ` Jens Axboe
-- strict thread matches above, loose matches on Subject: below --
2020-10-28 6:56 [PATCH RFC] blk-mq: Don't IPI requests on PREEMPT_RT 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
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