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From: John Garry <john.garry@huawei.com>
To: Ming Lei <ming.lei@redhat.com>, Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>, <linux-block@vger.kernel.org>,
	Bart Van Assche <bvanassche@acm.org>,
	Hannes Reinecke <hare@suse.com>,
	Thomas Gleixner <tglx@linutronix.de>, <will@kernel.org>,
	<peterz@infradead.org>, <paulmck@kernel.org>
Subject: Re: [PATCH V8 07/11] blk-mq: stop to handle IO and drain IO before hctx becomes inactive
Date: Sun, 26 Apr 2020 09:19:11 +0100	[thread overview]
Message-ID: <16514862-905f-2e3c-40b7-8d71ea89cf62@huawei.com> (raw)
In-Reply-To: <20200426020621.GA511475@T590>

On 26/04/2020 03:06, Ming Lei wrote:
> On Sat, Apr 25, 2020 at 05:48:32PM +0200, Christoph Hellwig wrote:
>> FYI, here is what I think we should be doing (but the memory model
>> experts please correct me):

Hi Ming,

>>
>>   - just drop the direct_issue flag and check for the CPU, which is
>>     cheap enough
> 
> That isn't correct because the CPU for running async queue may not be
> same with rq->mq_ctx->cpu since hctx->cpumask may include several CPUs
> and we run queue in RR style and it is really a normal case.
> 
> So I'd rather to keep 'direct_issue' flag given it is just a constant

How about changing the function argument name from 'direct_issue' to 
something which better expresses the intent, like 'may_migrate' or 
similar? (I know you mention the reason this in the comment also).

> argument and gcc is smart enough to optimize this case if you don't have
> better idea.
> 
>>   - replace the raw_smp_processor_id with a get_cpu to make sure we
>>     don't hit the tiny migration windows
> 

I do wonder if the barrier always may be cheaper than this.

> Will do that.
> 
>>   - a bunch of random cleanups to make the code easier to read, mostly
>>     by being more self-documenting or improving the comments.
> 
> The cleanup code looks fine.
> 
> 

Cheers,
John


  reply	other threads:[~2020-04-26  8:19 UTC|newest]

Thread overview: 80+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-24 10:23 [PATCH V8 00/11] blk-mq: improvement CPU hotplug Ming Lei
2020-04-24 10:23 ` [PATCH V8 01/11] block: clone nr_integrity_segments and write_hint in blk_rq_prep_clone Ming Lei
2020-04-24 10:32   ` Christoph Hellwig
2020-04-24 12:43   ` Hannes Reinecke
2020-04-24 16:11   ` Martin K. Petersen
2020-04-24 10:23 ` [PATCH V8 02/11] block: add helper for copying request Ming Lei
2020-04-24 10:35   ` Christoph Hellwig
2020-04-24 12:43   ` Hannes Reinecke
2020-04-24 16:12   ` Martin K. Petersen
2020-04-24 10:23 ` [PATCH V8 03/11] blk-mq: mark blk_mq_get_driver_tag as static Ming Lei
2020-04-24 12:44   ` Hannes Reinecke
2020-04-24 16:13   ` Martin K. Petersen
2020-04-24 10:23 ` [PATCH V8 04/11] blk-mq: assign rq->tag in blk_mq_get_driver_tag Ming Lei
2020-04-24 10:35   ` Christoph Hellwig
2020-04-24 13:02   ` Hannes Reinecke
2020-04-25  2:54     ` Ming Lei
2020-04-25 18:26       ` Hannes Reinecke
2020-04-24 10:23 ` [PATCH V8 05/11] blk-mq: support rq filter callback when iterating rqs Ming Lei
2020-04-24 13:17   ` Hannes Reinecke
2020-04-25  3:04     ` Ming Lei
2020-04-24 10:23 ` [PATCH V8 06/11] blk-mq: prepare for draining IO when hctx's all CPUs are offline Ming Lei
2020-04-24 13:23   ` Hannes Reinecke
2020-04-25  3:24     ` Ming Lei
2020-04-24 10:23 ` [PATCH V8 07/11] blk-mq: stop to handle IO and drain IO before hctx becomes inactive Ming Lei
2020-04-24 10:38   ` Christoph Hellwig
2020-04-25  3:17     ` Ming Lei
2020-04-25  8:32       ` Christoph Hellwig
2020-04-25  9:34         ` Ming Lei
2020-04-25  9:53           ` Ming Lei
2020-04-25 15:48             ` Christoph Hellwig
2020-04-26  2:06               ` Ming Lei
2020-04-26  8:19                 ` John Garry [this message]
2020-04-27 15:36                 ` Christoph Hellwig
2020-04-28  1:10                   ` Ming Lei
2020-04-27 19:03               ` Paul E. McKenney
2020-04-28  6:54                 ` Christoph Hellwig
2020-04-28 15:58               ` Peter Zijlstra
2020-04-29  2:16                 ` Ming Lei
2020-04-29  8:07                   ` Will Deacon
2020-04-29  9:46                     ` Ming Lei
2020-04-29 12:27                       ` Will Deacon
2020-04-29 13:43                         ` Ming Lei
2020-04-29 17:34                           ` Will Deacon
2020-04-30  0:39                             ` Ming Lei
2020-04-30 11:04                               ` Will Deacon
2020-04-30 14:02                                 ` Ming Lei
2020-05-05 15:46                                   ` Christoph Hellwig
2020-05-06  1:24                                     ` Ming Lei
2020-05-06  7:28                                       ` Will Deacon
2020-05-06  8:07                                         ` Ming Lei
2020-05-06  9:56                                           ` Will Deacon
2020-05-06 10:22                                             ` Ming Lei
2020-04-29 17:46                           ` Paul E. McKenney
2020-04-30  0:43                             ` Ming Lei
2020-04-24 13:27   ` Hannes Reinecke
2020-04-25  3:30     ` Ming Lei
2020-04-24 13:42   ` John Garry
2020-04-25  3:41     ` Ming Lei
2020-04-24 10:23 ` [PATCH V8 08/11] block: add blk_end_flush_machinery Ming Lei
2020-04-24 10:41   ` Christoph Hellwig
2020-04-25  3:44     ` Ming Lei
2020-04-25  8:11       ` Christoph Hellwig
2020-04-25  9:51         ` Ming Lei
2020-04-24 13:47   ` Hannes Reinecke
2020-04-25  3:47     ` Ming Lei
2020-04-24 10:23 ` [PATCH V8 09/11] blk-mq: add blk_mq_hctx_handle_dead_cpu for handling cpu dead Ming Lei
2020-04-24 10:42   ` Christoph Hellwig
2020-04-25  3:48     ` Ming Lei
2020-04-24 13:48   ` Hannes Reinecke
2020-04-24 10:23 ` [PATCH V8 10/11] blk-mq: re-submit IO in case that hctx is inactive Ming Lei
2020-04-24 10:44   ` Christoph Hellwig
2020-04-25  3:52     ` Ming Lei
2020-04-24 13:55   ` Hannes Reinecke
2020-04-25  3:59     ` Ming Lei
2020-04-24 10:23 ` [PATCH V8 11/11] block: deactivate hctx when the hctx is actually inactive Ming Lei
2020-04-24 10:43   ` Christoph Hellwig
2020-04-24 13:56   ` Hannes Reinecke
2020-04-24 15:23 ` [PATCH V8 00/11] blk-mq: improvement CPU hotplug Jens Axboe
2020-04-24 15:40   ` Christoph Hellwig
2020-04-24 15:41     ` Jens Axboe

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