From: Mel Gorman <mgorman@techsingularity.net>
To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
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] Revert "mm, page_alloc: only use per-cpu allocator for irq-safe requests"
Date: Sat, 15 Apr 2017 20:57:35 +0100 [thread overview]
Message-ID: <20170415195734.avk2zk237a2oe5cd@techsingularity.net> (raw)
In-Reply-To: <20170415212833.30ed3f2b@redhat.com>
On Sat, Apr 15, 2017 at 09:28:33PM +0200, Jesper Dangaard Brouer wrote:
> On Sat, 15 Apr 2017 15:53:50 +0100
> Mel Gorman <mgorman@techsingularity.net> wrote:
>
> > This reverts commit 374ad05ab64d696303cec5cc8ec3a65d457b7b1c. While the
> > patch worked great for userspace allocations, the fact that softirq loses
> > the per-cpu allocator caused problems. It needs to be redone taking into
> > account that a separate list is needed for hard/soft IRQs or alternatively
> > find a cheap way of detecting reentry due to an interrupt. Both are possible
> > but sufficiently tricky that it shouldn't be rushed. Jesper had one method
> > for allowing softirqs but reported that the cost was high enough that it
> > performed similarly to a plain revert. His figures for netperf TCP_STREAM
> > were as follows
> >
> > Baseline v4.10.0 : 60316 Mbit/s
> > Current 4.11.0-rc6: 47491 Mbit/s
> > This patch : 60662 Mbit/s
> (should instead state "Jesper's patch" or "His patch")
>
Yes, you are correct of course.
> Ran same test (8 parallel netperf TCP_STREAMs) with this patch applied:
>
> This patch 60106 Mbit/s (average of 7 iteration 60 sec runs)
>
> With these speeds I'm starting to hit the memory bandwidth of my machines.
> Thus, the 60 GBit/s measurement cannot be used to validate the
> performance impact of reverting this compared to my softirq patch, it
> only shows we fixed the regression. (I'm suspicious as I see a higher
> contention on the page allocator lock (4% vs 1.3%) with this patch and
> still same performance... but lets worry about that outside the rc-series).
>
Well, in itself that limitation highlights that evaluating this is
challenging and needs careful treatment. Otherwise two different
approaches can seem equivalent only because a hardware-related
bottleneck was at play.
--
Mel Gorman
SUSE Labs
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prev parent reply other threads:[~2017-04-15 19:57 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-15 14:53 [PATCH] Revert "mm, page_alloc: only use per-cpu allocator for irq-safe requests" Mel Gorman
2017-04-15 19:28 ` Jesper Dangaard Brouer
2017-04-15 19:57 ` Mel Gorman [this message]
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