From: David Laight <David.Laight@ACULAB.COM>
To: 'Arjun Roy' <arjunroy@google.com>, Eric Dumazet <edumazet@google.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Eric Dumazet <eric.dumazet@gmail.com>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
paulmck <paulmck@kernel.org>, Boqun Feng <boqun.feng@gmail.com>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v2 3/3] rseq: optimise rseq_get_rseq_cs() and clear_rseq_cs()
Date: Tue, 13 Apr 2021 21:19:10 +0000 [thread overview]
Message-ID: <feed2c13dbe34279a03929a588c46c67@AcuMS.aculab.com> (raw)
In-Reply-To: <CAOFY-A1=2MzHvmqBEo=WBT6gWc=KnmtCWogjLdwZVDTp-zDjBQ@mail.gmail.com>
> If we're special-casing 64-bit architectures anyways - unrolling the
> 32B copy_from_user() for struct rseq_cs appears to be roughly 5-10%
> savings on x86-64 when I measured it (well, in a microbenchmark, not
> in rseq_get_rseq_cs() directly). Perhaps that could be an additional
> avenue for improvement here.
The killer is usually 'user copy hardening'.
It significantly slows down sendmsg() and recvmsg().
I've got measurable performance improvements by
using __copy_from_user() when the buffer since has
already been checked - but isn't a compile-time constant.
There is also scope for using _get_user() when reading
iovec[] (instead of copy_from_user()) and doing all the
bound checks (etc) in the loop.
That gives a measurable improvement for writev("/dev/null").
I must sort those patches out again.
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:[~2021-04-13 21:19 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-13 16:22 [PATCH v2 0/3] rseq: minor optimizations Eric Dumazet
2021-04-13 16:22 ` [PATCH v2 1/3] rseq: optimize rseq_update_cpu_id() Eric Dumazet
2021-04-13 16:22 ` [PATCH v2 2/3] rseq: remove redundant access_ok() Eric Dumazet
2021-04-13 16:22 ` [PATCH v2 3/3] rseq: optimise rseq_get_rseq_cs() and clear_rseq_cs() Eric Dumazet
2021-04-13 16:54 ` Mathieu Desnoyers
2021-04-13 16:57 ` Eric Dumazet
2021-04-13 17:01 ` Eric Dumazet
2021-04-13 17:07 ` Eric Dumazet
2021-04-13 17:20 ` Mathieu Desnoyers
2021-04-13 17:33 ` Eric Dumazet
2021-04-13 18:00 ` Mathieu Desnoyers
2021-04-13 18:22 ` Eric Dumazet
2021-04-13 18:35 ` Arjun Roy
2021-04-13 21:19 ` David Laight [this message]
2021-04-13 22:03 ` Arjun Roy
2021-04-14 7:55 ` David Laight
2021-04-14 16:00 ` Eric Dumazet
2021-04-14 16:08 ` David Laight
2021-04-14 16:10 ` Eric Dumazet
2021-04-14 17:15 ` Arjun Roy
2021-04-14 17:35 ` Eric Dumazet
2021-04-14 20:15 ` Arjun Roy
2021-04-14 20:25 ` Eric Dumazet
2021-04-14 20:35 ` Arjun Roy
2021-04-13 19:13 ` Mathieu Desnoyers
2021-04-13 17:06 ` Mathieu Desnoyers
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