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From: Andi Kleen <andi@firstfloor.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>,
	Salman Qazi <sqazi@google.com>,
	davem@davemloft.net, linux-kernel@vger.kernel.org,
	Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Andi Kleen <andi@firstfloor.org>
Subject: Re: Performance regression in write() syscall
Date: Tue, 24 Feb 2009 17:24:43 +0100	[thread overview]
Message-ID: <20090224162443.GW26292@one.firstfloor.org> (raw)
In-Reply-To: <alpine.LFD.2.00.0902240744500.3111@localhost.localdomain>

On Tue, Feb 24, 2009 at 07:52:34AM -0800, Linus Torvalds wrote:
> 
> 
> On Tue, 24 Feb 2009, Nick Piggin wrote:
> >
> > > it does make some kind of sense to try to avoid the noncached versions for
> > > small writes - because small writes tend to be for temp-files.
> > 
> > I don't see the significance of a temp file. If the pagecache is truncated,
> > then the cachelines remain dirty and so you can't avoid an eventual store
> > back to RAM? 
> 
> No, because many small files end up being used as scratch-pads (think 
> shell script sequences etc), and get read back immediately again. Doing 
> non-temporal stores might just be bad simply because trying to play games 
> with caching may simply do the wrong thing.

I usually recommend to use shmfs for /tmp. Perhaps that should be done
more widely.

BTW I got some upcomming patches to improve c_*_u() and memcpy
on modern Intel x86 CPUs.

-Andi


  reply	other threads:[~2009-02-24 16:06 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-02-24  2:03 Performance regression in write() syscall Salman Qazi
2009-02-24  4:10 ` Nick Piggin
2009-02-24  4:28   ` Linus Torvalds
2009-02-24  9:02     ` Nick Piggin
2009-02-24 15:52       ` Linus Torvalds
2009-02-24 16:24         ` Andi Kleen [this message]
2009-02-24 16:51         ` Ingo Molnar
2009-02-25  3:23         ` Nick Piggin
2009-02-25  7:25           ` [patch] x86, mm: pass in 'total' to __copy_from_user_*nocache() Ingo Molnar
2009-02-25  8:09             ` Nick Piggin
2009-02-25  8:29               ` Ingo Molnar
2009-02-25  8:59                 ` Nick Piggin
2009-02-25 12:01                   ` Ingo Molnar
2009-02-25 16:04             ` Linus Torvalds
2009-02-25 16:29               ` Ingo Molnar
2009-02-27 12:05               ` Nick Piggin
2009-02-28  8:29                 ` Ingo Molnar
2009-02-28 11:49                   ` Nick Piggin
2009-02-28 12:58                     ` Ingo Molnar
2009-02-28 17:16                       ` Linus Torvalds
2009-02-28 17:24                         ` Arjan van de Ven
2009-02-28 17:42                           ` Linus Torvalds
2009-02-28 17:53                             ` Arjan van de Ven
2009-02-28 18:05                             ` Andi Kleen
2009-02-28 18:27                             ` Ingo Molnar
2009-02-28 18:39                               ` Arjan van de Ven
2009-03-02 10:39                                 ` [PATCH] x86, mm: dont use non-temporal stores in pagecache accesses Ingo Molnar
2009-02-28 18:52                               ` [patch] x86, mm: pass in 'total' to __copy_from_user_*nocache() Linus Torvalds
2009-03-01 14:19                                 ` Nick Piggin
2009-03-01  0:06                             ` David Miller
2009-03-01  0:40                               ` Andi Kleen
2009-03-01  0:28                                 ` H. Peter Anvin
2009-03-01  0:38                                   ` Arjan van de Ven
2009-03-01  1:48                                     ` Andi Kleen
2009-03-01  1:38                                       ` Arjan van de Ven
2009-03-01  1:40                                         ` H. Peter Anvin
2009-03-01 14:06                                           ` Nick Piggin
2009-03-02  4:46                                             ` H. Peter Anvin
2009-03-02  6:18                                               ` Nick Piggin
2009-03-02 21:16                                             ` Linus Torvalds
2009-03-02 21:25                                               ` Ingo Molnar
2009-03-03  4:30                                                 ` Nick Piggin
2009-03-03  4:20                                               ` Nick Piggin
2009-03-03  9:02                                                 ` Ingo Molnar
2009-03-04  3:37                                                   ` Nick Piggin
2009-03-01  2:07                                         ` Andi Kleen
2009-02-24  5:43   ` Performance regression in write() syscall Salman Qazi
2009-02-24 10:09 ` Andi Kleen
2009-02-24 16:13   ` Ingo Molnar
2009-02-24 16:51     ` Andi Kleen
     [not found] <c8UUh-6G-3@gated-at.bofh.it>
     [not found] ` <c92fh-3uD-15@gated-at.bofh.it>
2009-02-24 11:12   ` Bodo Eggert

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