From: David Laight <David.Laight@ACULAB.COM>
To: 'Eric Dumazet' <eric.dumazet@gmail.com>,
network dev <netdev@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: recvfrom/recvmsg performance and CONFIG_HARDENED_USERCOPY
Date: Mon, 9 Dec 2019 11:01:30 +0000 [thread overview]
Message-ID: <efffc167eff1475f94f745f733171d59@AcuMS.aculab.com> (raw)
In-Reply-To: <dc10298d-4280-b9b4-9203-be4000e85c42@gmail.com>
From: Eric Dumazet
> Sent: 06 December 2019 14:22
...
> Real question is : Do you actually need to use recvmsg() instead of recvfrom() ?
> If recvmsg() provides additional cmsg, this is not surprising it is more expensive.
Except I'm not passing in a buffer for it.
The reason I'm looking at recvmsg is that I'd like to use recvmmsg it order to
read out more than one message from a socket without doing an extra poll().
Note that I don't expect there to be a second message most of the time and
almost never a third one.
Although I think that will only ever 'win' if recvmmsg() called vfs_poll() to find
if there was more data to read before doing any of the copy_from_user() etc.
> recvmsg() also uses an indirect call, so CONFIG_RETPOLINE=y is probably hurting.
I don't have CONFIG_RETPOLINE enabled, the compiler I'm using is too old.
(gcc 4.7.3).
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2019-12-09 11:01 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-06 13:39 recvfrom/recvmsg performance and CONFIG_HARDENED_USERCOPY David Laight
2019-12-06 14:21 ` Eric Dumazet
2019-12-06 16:09 ` Paolo Abeni
2019-12-06 16:19 ` Eric Dumazet
2019-12-09 11:01 ` David Laight [this message]
2019-12-09 18:43 ` Andy Lutomirski
2019-12-10 10:21 ` David Laight
2019-12-09 15:05 ` David Laight
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