linux-mm.kvack.org archive mirror
 help / color / mirror / Atom feed
From: Andrew Morton <akpm@linux-foundation.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: brouer@redhat.com, willy@infradead.org, peterz@infradead.org,
	pagupta@redhat.com, ttoukan.linux@gmail.com, tariqt@mellanox.com,
	netdev@vger.kernel.org, saeedm@mellanox.com,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm, page_alloc: re-enable softirq use of per-cpu page allocator
Date: Mon, 10 Apr 2017 14:26:16 -0700	[thread overview]
Message-ID: <20170410142616.6d37a11904dd153298cf7f3b@linux-foundation.org> (raw)
In-Reply-To: <20170410150821.vcjlz7ntabtfsumm@techsingularity.net>

On Mon, 10 Apr 2017 16:08:21 +0100 Mel Gorman <mgorman@techsingularity.net> wrote:

> IRQ context were excluded from using the Per-Cpu-Pages (PCP) lists caching
> of order-0 pages in commit 374ad05ab64d ("mm, page_alloc: only use per-cpu
> allocator for irq-safe requests").
> 
> This unfortunately also included excluded SoftIRQ.  This hurt the performance
> for the use-case of refilling DMA RX rings in softirq context.

Out of curiosity: by how much did it "hurt"?

<ruffles through the archives>

Tariq found:

: I disabled the page-cache (recycle) mechanism to stress the page
: allocator, and see a drastic degradation in BW, from 47.5 G in v4.10 to
: 31.4 G in v4.11-rc1 (34% drop).

then with this patch he found

: It looks very good!  I get line-rate (94Gbits/sec) with 8 streams, in
: comparison to less than 55Gbits/sec before.

Can I take this to mean that the page allocator's per-cpu-pages feature
ended up doubling the performance of this driver?  Better than the
driver's private page recycling?  I'd like to believe that, but am
having trouble doing so ;)

> This patch re-allow softirq context, which should be safe by disabling
> BH/softirq, while accessing the list.  PCP-lists access from both hard-IRQ
> and NMI context must not be allowed.  Peter Zijlstra says in_nmi() code
> never access the page allocator, thus it should be sufficient to only test
> for !in_irq().
> 
> One concern with this change is adding a BH (enable) scheduling point at
> both PCP alloc and free. If further concerns are highlighted by this patch,
> the result wiill be to revert 374ad05ab64d and try again at a later date
> to offset the irq enable/disable overhead.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

  parent reply	other threads:[~2017-04-10 21:26 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-10 15:08 [PATCH] mm, page_alloc: re-enable softirq use of per-cpu page allocator Mel Gorman
2017-04-10 20:53 ` Jesper Dangaard Brouer
2017-04-11  8:23   ` Mel Gorman
2017-04-10 21:26 ` Andrew Morton [this message]
2017-04-14 10:10   ` Jesper Dangaard Brouer
2017-04-15 15:03     ` Mel Gorman

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=20170410142616.6d37a11904dd153298cf7f3b@linux-foundation.org \
    --to=akpm@linux-foundation.org \
    --cc=brouer@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mgorman@techsingularity.net \
    --cc=netdev@vger.kernel.org \
    --cc=pagupta@redhat.com \
    --cc=peterz@infradead.org \
    --cc=saeedm@mellanox.com \
    --cc=tariqt@mellanox.com \
    --cc=ttoukan.linux@gmail.com \
    --cc=willy@infradead.org \
    /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).