From: David Laight <David.Laight@ACULAB.COM>
To: 'Denys Vlasenko' <dvlasenk@redhat.com>,
Jens Axboe <axboe@kernel.dk>, "Ingo Molnar" <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
"the arch/x86 maintainers" <x86@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Brian Gerst <brgerst@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"pabeni@redhat.com" <pabeni@redhat.com>
Subject: RE: [PATCH] x86: only use ERMS for user copies for larger sizes
Date: Thu, 22 Nov 2018 17:36:37 +0000 [thread overview]
Message-ID: <7ea44458b90b4d41a08ba9012818d273@AcuMS.aculab.com> (raw)
In-Reply-To: <26eff539-7de7-784c-0c88-f1d30753299d@redhat.com>
From: Denys Vlasenko
> Sent: 21 November 2018 13:44
...
> I also tested this while working for string ops code in musl.
>
> I think at least 128 bytes would be the minimum where "REP insn"
> are more efficient. In my testing, it's more like 256 bytes...
What happens for misaligned copies?
I had a feeling that the ERMS 'reb movsb' code used some kind
of barrel shifter in that case.
The other problem with the ERMS copy is that it gets used
for copy_to/from_io() - and the 'rep movsb' on uncached
locations has to do byte copies.
Byte reads on PCIe are really horrid.
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:[~2018-11-22 17:36 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <02bfc577-32a5-66be-64bf-d476b7d447d2@kernel.dk>
2018-11-20 20:24 ` [PATCH] x86: only use ERMS for user copies for larger sizes Jens Axboe
2018-11-21 6:36 ` Ingo Molnar
2018-11-21 13:32 ` Jens Axboe
2018-11-21 13:44 ` Denys Vlasenko
2018-11-22 17:36 ` David Laight [this message]
2018-11-22 17:52 ` Linus Torvalds
2018-11-22 18:06 ` Andy Lutomirski
2018-11-22 18:58 ` Linus Torvalds
2018-11-23 9:34 ` David Laight
2018-11-23 10:12 ` David Laight
2018-11-23 16:36 ` Linus Torvalds
2018-11-23 17:42 ` Linus Torvalds
2018-11-23 18:39 ` Andy Lutomirski
2018-11-23 18:44 ` Linus Torvalds
2018-11-23 19:11 ` Andy Lutomirski
2018-11-26 10:12 ` David Laight
2018-11-26 10:01 ` David Laight
2018-11-26 10:26 ` David Laight
2019-01-05 2:38 ` Linus Torvalds
2019-01-07 9:55 ` David Laight
2019-01-07 17:43 ` Linus Torvalds
2019-01-08 9:10 ` David Laight
2019-01-08 18:01 ` Linus Torvalds
2018-11-21 13:45 ` Paolo Abeni
2018-11-21 17:27 ` Linus Torvalds
2018-11-21 18:04 ` Jens Axboe
2018-11-21 18:26 ` Andy Lutomirski
2018-11-21 18:43 ` Linus Torvalds
2018-11-21 22:38 ` Andy Lutomirski
2018-11-21 18:16 ` Linus Torvalds
2018-11-21 19:01 ` Linus Torvalds
2018-11-22 10:32 ` Ingo Molnar
2018-11-22 11:13 ` Ingo Molnar
2018-11-22 11:21 ` Ingo Molnar
2018-11-23 16:40 ` Josh Poimboeuf
2018-11-22 16:55 ` Linus Torvalds
2018-11-22 17:26 ` Andy Lutomirski
2018-11-22 17:35 ` Linus Torvalds
2018-11-24 6:09 ` Jens Axboe
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