linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Jens Axboe <axboe@kernel.dk>
To: Jianchao Wang <jianchao.w.wang@oracle.com>
Cc: ming.lei@redhat.com, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH V6 3/5] blk-mq: ensure hctx to be ran on mapped cpu when issue directly
Date: Tue, 13 Nov 2018 06:44:46 -0700	[thread overview]
Message-ID: <d8d88eff-e3eb-542d-d4fa-06b6aff97ba0@kernel.dk> (raw)
In-Reply-To: <1542103016-21037-4-git-send-email-jianchao.w.wang@oracle.com>

On 11/13/18 2:56 AM, Jianchao Wang wrote:
> When issue request directly and the task is migrated out of the
> original cpu where it allocates request, hctx could be ran on
> the cpu where it is not mapped.
> To fix this,
>  - insert the request forcibly if BLK_MQ_F_BLOCKING is set.
>  - check whether the current is mapped to the hctx, if not, insert
>    forcibly.
>  - invoke __blk_mq_issue_directly under preemption disabled.

I'm not too crazy about this one, adding a get/put_cpu() in the hot
path, and a cpumask test. The fact is that most/no drivers care
about strict placement. We always try to do so, if convenient,
since it's faster, but this seems to be doing the opposite.

I'd be more inclined to have a driver flag if it needs guaranteed
placement, using one an ops BLK_MQ_F_STRICT_CPU flag or similar.

What do you think?

-- 
Jens Axboe


  reply	other threads:[~2018-11-13 13:44 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-13  9:56 [PATCH V6 0/5] blk-mq: refactor and fix on issue request directly Jianchao Wang
2018-11-13  9:56 ` [PATCH V6 1/5] blk-mq: refactor the code of " Jianchao Wang
2018-11-13  9:56 ` [PATCH V6 2/5] blk-mq: fix issue directly case when q is stopped or quiesced Jianchao Wang
2018-11-13  9:56 ` [PATCH V6 3/5] blk-mq: ensure hctx to be ran on mapped cpu when issue directly Jianchao Wang
2018-11-13 13:44   ` Jens Axboe [this message]
2018-11-14  2:15     ` jianchao.wang
2018-11-14  3:02       ` Ming Lei
2018-11-14  3:38         ` jianchao.wang
2018-11-13  9:56 ` [PATCH V6 4/5] blk-mq: issue directly with bypass 'false' in blk_mq_sched_insert_requests Jianchao Wang
2018-11-13  9:56 ` [PATCH V6 5/5] blk-mq: replace and kill blk_mq_request_issue_directly Jianchao Wang

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=d8d88eff-e3eb-542d-d4fa-06b6aff97ba0@kernel.dk \
    --to=axboe@kernel.dk \
    --cc=jianchao.w.wang@oracle.com \
    --cc=linux-block@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=ming.lei@redhat.com \
    --subject='Re: [PATCH V6 3/5] blk-mq: ensure hctx to be ran on mapped cpu when issue directly' \
    /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

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).