From: John Garry <john.garry@huawei.com>
To: <axboe@kernel.dk>, <kashyap.desai@broadcom.com>
Cc: <linux-block@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<ming.lei@redhat.com>, <hare@suse.de>
Subject: Re: [PATCH RFT 0/3] blk-mq: Optimise blk_mq_queue_tag_busy_iter() for shared tags
Date: Mon, 15 Nov 2021 15:56:16 +0000 [thread overview]
Message-ID: <7fba1b1e-63a6-6315-e5ca-6d5ae9de6dbb@huawei.com> (raw)
In-Reply-To: <1635852455-39935-1-git-send-email-john.garry@huawei.com>
On 02/11/2021 11:27, John Garry wrote:
Hi Kashyap,
Any chance you can try this series or give an update on the issue
reported earlier?
thanks @ Ming for the reviews.
Cheers,
John
> In [0], Kashyap reports high CPU usage for blk_mq_queue_tag_busy_iter()
> and callees for shared tags.
>
> Indeed blk_mq_queue_tag_busy_iter() would be less optimum for moving to
> shared tags, but it was not optimum previously.
>
> So I would like this series tested, and also to know what is triggering
> blk_mq_queue_tag_busy_iter() from userspace to cause such high CPU
> loading.
>
> As suggested by Ming, reading /proc/diskstats in a while true loop
> can trigger blk_mq_queue_tag_busy_iter(); I do so in a test with 2x
> separate consoles, and here are the results:
>
> v5.15
> blk_mq_queue_tag_busy_iter() 6.2%
> part_stat_read_all() 6.7
>
> pre-v5.16 (Linus' master branch @ commit bfc484fe6abb)
> blk_mq_queue_tag_busy_iter() 4.5%
> part_stat_read_all() 6.2
>
> pre-v5.16+this series
> blk_mq_queue_tag_busy_iter() not shown in top users
> part_stat_read_all() 7.5%
>
> These results are from perf top, on a system with 7x
> disks, with hisi_sas which has 16x HW queues.
>
> [0] https://lore.kernel.org/linux-block/e4e92abbe9d52bcba6b8cc6c91c442cc@mail.gmail.com/
>
> John Garry (3):
> blk-mq: Drop busy_iter_fn blk_mq_hw_ctx argument
> blk-mq: Delete busy_iter_fn
> blk-mq: Optimise blk_mq_queue_tag_busy_iter() for shared tags
>
> block/blk-mq-tag.c | 58 +++++++++++++++++++++++++++---------------
> block/blk-mq-tag.h | 2 +-
> block/blk-mq.c | 17 ++++++-------
> include/linux/blk-mq.h | 2 --
> 4 files changed, 47 insertions(+), 32 deletions(-)
>
next prev parent reply other threads:[~2021-11-15 15:56 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-02 11:27 [PATCH RFT 0/3] blk-mq: Optimise blk_mq_queue_tag_busy_iter() for shared tags John Garry
2021-11-02 11:27 ` [PATCH RFT 1/3] blk-mq: Drop busy_iter_fn blk_mq_hw_ctx argument John Garry
2021-11-09 3:02 ` Ming Lei
2021-11-28 10:39 ` Hannes Reinecke
2021-11-02 11:27 ` [PATCH RFT 2/3] blk-mq: Delete busy_iter_fn John Garry
2021-11-09 3:05 ` Ming Lei
2021-11-28 10:40 ` Hannes Reinecke
2021-11-02 11:27 ` [PATCH RFT 3/3] blk-mq: Optimise blk_mq_queue_tag_busy_iter() for shared tags John Garry
2021-11-28 10:43 ` Hannes Reinecke
2021-11-29 2:19 ` Ming Lei
2021-11-15 15:56 ` John Garry [this message]
2021-11-15 16:31 ` [PATCH RFT 0/3] " Kashyap Desai
2021-11-25 13:46 ` Kashyap Desai
2021-11-25 14:09 ` John Garry
2021-11-26 11:25 ` Kashyap Desai
2021-11-26 11:51 ` John Garry
2021-12-06 9:57 ` John Garry
2021-12-06 10:03 ` Kashyap Desai
2021-12-08 13:04 ` John Garry
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