From: Ming Lei <email@example.com> To: Jan Kara <firstname.lastname@example.org> Cc: Jens Axboe <email@example.com>, firstname.lastname@example.org, Khazhy Kumykov <email@example.com>, Paolo Valente <firstname.lastname@example.org> Subject: Re: [PATCH 1/2] block: Do not merge recursively in elv_attempt_insert_merge() Date: Fri, 21 May 2021 08:42:16 +0800 [thread overview] Message-ID: <YKcB6Hxhe3a1St31@T590> (raw) In-Reply-To: <email@example.com> On Fri, May 21, 2021 at 12:33:52AM +0200, Jan Kara wrote: > Most of the merging happens at bio level. There should not be much > merging happening at request level anymore. Furthermore if we backmerged > a request to the previous one, the chances to be able to merge the > result to even previous request are slim - that could succeed only if > requests were inserted in 2 1 3 order. Merging more requests in Right, but some workload has this kind of pattern. For example of qemu IO emulation, it often can be thought as single job, native aio, direct io with high queue depth. IOs is originated from one VM, but may be from multiple jobs in the VM, so bio merge may not hit much because of IO emulation timing(virtio-scsi/blk's MQ, or IO can be interleaved from multiple jobs via the SQ transport), but request merge can really make a difference, see recent patch in the following link: https://firstname.lastname@example.org/T/#t > elv_attempt_insert_merge() will be difficult to handle when we want to > pass requests to free back to the caller of > blk_mq_sched_try_insert_merge(). So just remove the possibility of > merging multiple requests in elv_attempt_insert_merge(). This way will cause regression. Thanks, Ming
next prev parent reply other threads:[~2021-05-21 0:42 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-05-20 22:33 [PATCH 0/2] block: Fix deadlock when merging requests with BFQ Jan Kara 2021-05-20 22:33 ` [PATCH 1/2] block: Do not merge recursively in elv_attempt_insert_merge() Jan Kara 2021-05-21 0:42 ` Ming Lei [this message] 2021-05-21 11:53 ` Jan Kara 2021-05-21 13:12 ` Ming Lei 2021-05-21 13:44 ` Jan Kara 2021-05-20 22:33 ` [PATCH 2/2] blk: Fix lock inversion between ioc lock and bfqd lock Jan Kara 2021-05-21 0:57 ` Ming Lei 2021-05-21 3:29 ` Khazhy Kumykov 2021-05-21 6:54 ` Ming Lei 2021-05-21 12:05 ` Jan Kara 2021-05-21 13:36 ` Ming Lei 2021-05-21 13:47 ` Jan Kara
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