From: Jens Axboe <axboe@kernel.dk>
To: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Cc: Huang Ying <ying.huang@intel.com>, Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: random call_single_data alignment
Date: Wed, 20 Dec 2017 12:40:25 -0700 [thread overview]
Message-ID: <3875cde5-a193-6aa6-1f9e-561cc66110f2@kernel.dk> (raw)
In-Reply-To: <a9beb452-7344-9e2d-fc80-094d8f5a0394@kernel.dk>
On 12/20/17 12:10 PM, Jens Axboe wrote:
> For some reason, commit 966a967116e6 was added to the tree without
> CC'ing relevant maintainers, even though it's touching random subsystems.
> One example is struct request, a core structure in the block layer.
> After this change, struct request grows from 296 to 320 bytes on my
> setup.
>
> Why are we blindly aligning to 32 bytes? The comment says to avoid
> it spanning two cache lines - but if that's the case, look at the
> actual use case and see if that's actually a problem. For struct
> request, it is not.
>
> Seems to me, this should have been applied in the specific area
> where it was needed. Keep struct call_single_data (instead of some
> __ version), and just manually align it where it matters.
https://marc.info/?l=linux-block&m=151379793913822&w=2
https://marc.info/?l=linux-block&m=151379849914002&w=2
In the future, please CC the relevant folks before making (and
committing) changes like that.
--
Jens Axboe
next prev parent reply other threads:[~2017-12-20 19:40 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-20 19:10 random call_single_data alignment Jens Axboe
2017-12-20 19:40 ` Jens Axboe [this message]
2017-12-20 20:18 ` Peter Zijlstra
2017-12-20 20:23 ` Jens Axboe
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=3875cde5-a193-6aa6-1f9e-561cc66110f2@kernel.dk \
--to=axboe@kernel.dk \
--cc=linux-block@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=ying.huang@intel.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