From: Hannes Reinecke <hare@suse.de>
To: John Garry <john.garry@huawei.com>, axboe@kernel.dk
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
ming.lei@redhat.com, kashyap.desai@broadcom.com
Subject: Re: [PATCH RFT 3/3] blk-mq: Optimise blk_mq_queue_tag_busy_iter() for shared tags
Date: Sun, 28 Nov 2021 11:43:30 +0100 [thread overview]
Message-ID: <95685711-ee3c-f1ec-4329-47e8e789a08a@suse.de> (raw)
In-Reply-To: <1635852455-39935-4-git-send-email-john.garry@huawei.com>
On 11/2/21 12:27 PM, John Garry wrote:
> Kashyap reports high CPU usage in blk_mq_queue_tag_busy_iter() and callees
> using megaraid SAS RAID card since moving to shared tags [0].
>
> Previously, when shared tags was shared sbitmap, this function was less
> than optimum since we would iter through all tags for all hctx's,
> yet only ever match upto tagset depth number of rqs.
>
> Since the change to shared tags, things are even less efficient if we have
> parallel callers of blk_mq_queue_tag_busy_iter(). This is because in
> bt_iter() -> blk_mq_find_and_get_req() there would be more contention on
> accessing each request ref and tags->lock since they are now shared among
> all HW queues.
>
> Optimise by having separate calls to bt_for_each() for when we're using
> shared tags. In this case no longer pass a hctx, as it is no longer
> relevant, and teach bt_iter() about this.
>
> Ming suggested something along the lines of this change, apart from a
> different implementation.
>
> [0] https://lore.kernel.org/linux-block/e4e92abbe9d52bcba6b8cc6c91c442cc@mail.gmail.com/
>
> Signed-off-by: John Garry <john.garry@huawei.com>
> ---
> block/blk-mq-tag.c | 52 +++++++++++++++++++++++++++++++---------------
> 1 file changed, 35 insertions(+), 17 deletions(-)
>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer
next prev parent reply other threads:[~2021-11-28 10:45 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 [this message]
2021-11-29 2:19 ` Ming Lei
2021-11-15 15:56 ` [PATCH RFT 0/3] " John Garry
2021-11-15 16:31 ` 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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=95685711-ee3c-f1ec-4329-47e8e789a08a@suse.de \
--to=hare@suse.de \
--cc=axboe@kernel.dk \
--cc=john.garry@huawei.com \
--cc=kashyap.desai@broadcom.com \
--cc=linux-block@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=ming.lei@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).