From: David Miller <davem@davemloft.net>
To: edumazet@google.com
Cc: netdev@vger.kernel.org, eric.dumazet@gmail.com,
soheil@google.com, arjunroy@google.com
Subject: Re: [PATCH net-next] selftests: net: avoid ptl lock contention in tcp_mmap
Date: Sat, 16 Nov 2019 13:13:09 -0800 (PST) [thread overview]
Message-ID: <20191116.131309.972370574405253412.davem@davemloft.net> (raw)
In-Reply-To: <20191116015554.51077-1-edumazet@google.com>
From: Eric Dumazet <edumazet@google.com>
Date: Fri, 15 Nov 2019 17:55:54 -0800
> tcp_mmap is used as a reference program for TCP rx zerocopy,
> so it is important to point out some potential issues.
>
> If multiple threads are concurrently using getsockopt(...
> TCP_ZEROCOPY_RECEIVE), there is a chance the low-level mm
> functions compete on shared ptl lock, if vma are arbitrary placed.
>
> Instead of letting the mm layer place the chunks back to back,
> this patch enforces an alignment so that each thread uses
> a different ptl lock.
>
> Performance measured on a 100 Gbit NIC, with 8 tcp_mmap clients
> launched at the same time :
>
> $ for f in {1..8}; do ./tcp_mmap -H 2002:a05:6608:290:: & done
>
> In the following run, we reproduce the old behavior by requesting no alignment :
>
> $ tcp_mmap -sz -C $((128*1024)) -a 4096
...
> New behavior (automatic alignment based on Hugepagesize),
> we can see the system overhead being dramatically reduced.
>
> $ tcp_mmap -sz -C $((128*1024))
...
> Signed-off-by: Eric Dumazet <edumazet@google.com>
Applied, thanks Eric.
prev parent reply other threads:[~2019-11-16 21:13 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-16 1:55 [PATCH net-next] selftests: net: avoid ptl lock contention in tcp_mmap Eric Dumazet
2019-11-16 2:07 ` Soheil Hassas Yeganeh
2019-11-16 21:13 ` David Miller [this message]
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