From: Jens Axboe <axboe@kernel.dk> To: Ming Lei <ming.lei@redhat.com> Cc: Keith Busch <keith.busch@intel.com>, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>, Bart Van Assche <bart.vanassche@wdc.com> Subject: Re: [RFC PATCH 3/3] blk-mq: Remove generation seqeunce Date: Mon, 21 May 2018 21:51:19 -0600 [thread overview] Message-ID: <29D40550-AF2A-4357-B87F-95C28259A334@kernel.dk> (raw) In-Reply-To: <20180522034727.GE20430@ming.t460p> On May 21, 2018, at 9:47 PM, Ming Lei <ming.lei@redhat.com> wrote: >=20 >> On Mon, May 21, 2018 at 09:16:33PM -0600, Jens Axboe wrote: >>> On 5/21/18 8:49 PM, Ming Lei wrote: >>>> On Mon, May 21, 2018 at 05:11:31PM -0600, Keith Busch wrote: >>>> This patch simplifies the timeout handling by relying on the request >>>> reference counting to ensure the iterator is operating on an inflight >>>=20 >>> The reference counting isn't free, what is the real benefit in this way?= >>=20 >> Neither is the current scheme and locking, and this is a hell of a lot >> simpler. I'd get rid of the kref stuff and just do a simple >> atomic_dec_and_test(). Most of the time we should be uncontended on >> that, which would make it pretty darn cheap. I'd be surprised if it >> wasn't better than the current alternatives. >=20 > The explicit memory barriers by atomic_dec_and_test() isn't free. I=E2=80=99m not saying it=E2=80=99s free. Neither is our current synchroniza= tion. > Also the double completion issue need to be fixed before discussing > this approach further. Certainly. Also not saying that the current patch is perfect. But it=E2=80=99= s a lot more palatable than the alternatives, hence my interest. And I=E2=80= =99d like for this issue to get solved, we seem to be a bit stuck atm.=20 I=E2=80=99ll take a closer look tomorrow.=20
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From: axboe@kernel.dk (Jens Axboe) Subject: [RFC PATCH 3/3] blk-mq: Remove generation seqeunce Date: Mon, 21 May 2018 21:51:19 -0600 [thread overview] Message-ID: <29D40550-AF2A-4357-B87F-95C28259A334@kernel.dk> (raw) In-Reply-To: <20180522034727.GE20430@ming.t460p> On May 21, 2018,@9:47 PM, Ming Lei <ming.lei@redhat.com> wrote: > >> On Mon, May 21, 2018@09:16:33PM -0600, Jens Axboe wrote: >>> On 5/21/18 8:49 PM, Ming Lei wrote: >>>> On Mon, May 21, 2018@05:11:31PM -0600, Keith Busch wrote: >>>> This patch simplifies the timeout handling by relying on the request >>>> reference counting to ensure the iterator is operating on an inflight >>> >>> The reference counting isn't free, what is the real benefit in this way? >> >> Neither is the current scheme and locking, and this is a hell of a lot >> simpler. I'd get rid of the kref stuff and just do a simple >> atomic_dec_and_test(). Most of the time we should be uncontended on >> that, which would make it pretty darn cheap. I'd be surprised if it >> wasn't better than the current alternatives. > > The explicit memory barriers by atomic_dec_and_test() isn't free. I?m not saying it?s free. Neither is our current synchronization. > Also the double completion issue need to be fixed before discussing > this approach further. Certainly. Also not saying that the current patch is perfect. But it?s a lot more palatable than the alternatives, hence my interest. And I?d like for this issue to get solved, we seem to be a bit stuck atm. I?ll take a closer look tomorrow.
next prev parent reply other threads:[~2018-05-22 3:51 UTC|newest] Thread overview: 128+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-05-21 23:11 [RFC PATCH 0/3] blk-mq: Timeout rework Keith Busch 2018-05-21 23:11 ` Keith Busch 2018-05-21 23:11 ` [RFC PATCH 1/3] blk-mq: Reference count request usage Keith Busch 2018-05-21 23:11 ` Keith Busch 2018-05-22 2:27 ` Ming Lei 2018-05-22 2:27 ` Ming Lei 2018-05-22 15:19 ` Christoph Hellwig 2018-05-22 15:19 ` Christoph Hellwig 2018-05-21 23:11 ` [RFC PATCH 2/3] blk-mq: Fix timeout and state order Keith Busch 2018-05-21 23:11 ` Keith Busch 2018-05-22 2:28 ` Ming Lei 2018-05-22 2:28 ` Ming Lei 2018-05-22 15:24 ` Christoph Hellwig 2018-05-22 15:24 ` Christoph Hellwig 2018-05-22 16:27 ` Bart Van Assche 2018-05-22 16:27 ` Bart Van Assche 2018-05-21 23:11 ` [RFC PATCH 3/3] blk-mq: Remove generation seqeunce Keith Busch 2018-05-21 23:11 ` Keith Busch 2018-05-21 23:29 ` Bart Van Assche 2018-05-21 23:29 ` Bart Van Assche 2018-05-22 14:15 ` Keith Busch 2018-05-22 14:15 ` Keith Busch 2018-05-22 16:29 ` Bart Van Assche 2018-05-22 16:29 ` Bart Van Assche 2018-05-22 16:34 ` Keith Busch 2018-05-22 16:34 ` Keith Busch 2018-05-22 16:48 ` Bart Van Assche 2018-05-22 16:48 ` Bart Van Assche 2018-05-22 2:49 ` Ming Lei 2018-05-22 2:49 ` Ming Lei 2018-05-22 3:16 ` Jens Axboe 2018-05-22 3:16 ` Jens Axboe 2018-05-22 3:47 ` Ming Lei 2018-05-22 3:47 ` Ming Lei 2018-05-22 3:51 ` Jens Axboe [this message] 2018-05-22 3:51 ` Jens Axboe 2018-05-22 8:51 ` Ming Lei 2018-05-22 8:51 ` Ming Lei 2018-05-22 14:35 ` Jens Axboe 2018-05-22 14:35 ` Jens Axboe 2018-05-22 14:20 ` Keith Busch 2018-05-22 14:20 ` Keith Busch 2018-05-22 14:37 ` Ming Lei 2018-05-22 14:37 ` Ming Lei 2018-05-22 14:46 ` Keith Busch 2018-05-22 14:46 ` Keith Busch 2018-05-22 14:57 ` Ming Lei 2018-05-22 14:57 ` Ming Lei 2018-05-22 15:01 ` Keith Busch 2018-05-22 15:01 ` Keith Busch 2018-05-22 15:07 ` Ming Lei 2018-05-22 15:07 ` Ming Lei 2018-05-22 15:17 ` Keith Busch 2018-05-22 15:17 ` Keith Busch 2018-05-22 15:23 ` Ming Lei 2018-05-22 15:23 ` Ming Lei 2018-05-22 16:17 ` Christoph Hellwig 2018-05-22 16:17 ` Christoph Hellwig 2018-05-23 0:34 ` Ming Lei 2018-05-23 0:34 ` Ming Lei 2018-05-23 14:35 ` Keith Busch 2018-05-23 14:35 ` Keith Busch 2018-05-24 1:52 ` Ming Lei 2018-05-24 1:52 ` Ming Lei 2018-05-23 5:48 ` Hannes Reinecke 2018-05-23 5:48 ` Hannes Reinecke 2018-07-12 18:16 ` Bart Van Assche 2018-07-12 18:16 ` Bart Van Assche 2018-07-12 19:24 ` Keith Busch 2018-07-12 19:24 ` Keith Busch 2018-07-12 22:24 ` Bart Van Assche 2018-07-12 22:24 ` Bart Van Assche 2018-07-13 1:12 ` jianchao.wang 2018-07-13 1:12 ` jianchao.wang 2018-07-13 2:40 ` jianchao.wang 2018-07-13 2:40 ` jianchao.wang 2018-07-13 15:43 ` Keith Busch 2018-07-13 15:43 ` Keith Busch 2018-07-13 15:52 ` Bart Van Assche 2018-07-13 15:52 ` Bart Van Assche 2018-07-13 18:47 ` Keith Busch 2018-07-13 18:47 ` Keith Busch 2018-07-13 23:03 ` Bart Van Assche 2018-07-13 23:03 ` Bart Van Assche 2018-07-13 23:58 ` Keith Busch 2018-07-13 23:58 ` Keith Busch 2018-07-18 19:56 ` hch 2018-07-18 19:56 ` hch 2018-07-18 20:39 ` hch 2018-07-18 20:39 ` hch 2018-07-18 21:05 ` Bart Van Assche 2018-07-18 21:05 ` Bart Van Assche 2018-07-18 22:53 ` Keith Busch 2018-07-18 22:53 ` Keith Busch 2018-07-18 20:53 ` Keith Busch 2018-07-18 20:53 ` Keith Busch 2018-07-18 20:58 ` Bart Van Assche 2018-07-18 20:58 ` Bart Van Assche 2018-07-18 21:17 ` Keith Busch 2018-07-18 21:17 ` Keith Busch 2018-07-18 21:30 ` Bart Van Assche 2018-07-18 21:30 ` Bart Van Assche 2018-07-18 21:33 ` Keith Busch 2018-07-18 21:33 ` Keith Busch 2018-07-19 13:19 ` hch 2018-07-19 13:19 ` hch 2018-07-19 14:59 ` Keith Busch 2018-07-19 14:59 ` Keith Busch 2018-07-19 15:56 ` Keith Busch 2018-07-19 15:56 ` Keith Busch 2018-07-19 16:04 ` Bart Van Assche 2018-07-19 16:04 ` Bart Van Assche 2018-07-19 16:22 ` Keith Busch 2018-07-19 16:22 ` Keith Busch 2018-07-19 16:29 ` hch 2018-07-19 16:29 ` hch 2018-07-19 20:18 ` Keith Busch 2018-07-19 20:18 ` Keith Busch 2018-07-19 13:22 ` hch 2018-07-19 13:22 ` hch 2018-05-21 23:29 ` [RFC PATCH 0/3] blk-mq: Timeout rework Bart Van Assche 2018-05-21 23:29 ` Bart Van Assche 2018-05-22 14:06 ` Keith Busch 2018-05-22 14:06 ` Keith Busch 2018-05-22 16:30 ` Bart Van Assche 2018-05-22 16:30 ` Bart Van Assche 2018-05-22 16:44 ` Keith Busch 2018-05-22 16:44 ` Keith Busch
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