From: Andrew Morton <akpm@zip.com.au>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Linus Torvalds <torvalds@transmeta.com>,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: [patch 4/21] fix ARCH_HAS_PREFETCH
Date: Sun, 11 Aug 2002 11:47:22 -0700 [thread overview]
Message-ID: <3D56B13A.D3F741D1@zip.com.au> (raw)
In-Reply-To: 1029095396.16216.18.camel@irongate.swansea.linux.org.uk
Alan Cox wrote:
>
> On Sun, 2002-08-11 at 08:38, Andrew Morton wrote:
> > This information loss is unfortunate. Examples:
> >
> > for (i = 0; i < N; i++)
> > prefetch(foo[i]);
> >
> > Problem is, if `prefetch' is a no-op, the compiler will still
> > generate an empty busy-wait loop. Which it must do.
>
> Why - nothing there is volatile
Because the compiler sees:
for (i = 0; i < N; i++)
;
and it says "ah ha. A busy wait delay loop" and leaves it alone.
It's actually a special-case inside the compiler to not optimise
away such constructs.
next prev parent reply other threads:[~2002-08-11 18:33 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-08-11 7:38 [patch 4/21] fix ARCH_HAS_PREFETCH Andrew Morton
2002-08-11 19:49 ` Alan Cox
2002-08-11 18:47 ` Andrew Morton [this message]
2002-08-11 18:46 ` Larry McVoy
2002-08-11 19:06 ` Linus Torvalds
2002-08-11 20:07 ` GCC still keeps empty loops? (was: [patch 4/21] fix ARCH_HAS_PREFETCH) Jamie Lokier
2002-08-12 7:45 ` Ralf Baechle
2002-08-13 21:42 ` [patch 4/21] fix ARCH_HAS_PREFETCH Adrian Bunk
2002-08-13 22:12 ` H. Peter Anvin
2002-08-13 22:22 ` Adrian Bunk
2002-08-13 22:42 ` H. Peter Anvin
2002-08-14 17:40 ` Rogier Wolff
2002-08-14 19:41 ` H. Peter Anvin
2002-08-14 19:57 ` Jamie Lokier
2002-08-14 22:03 ` Daniel Jacobowitz
2002-08-14 20:45 ` Willy Tarreau
2002-08-14 20:58 ` H. Peter Anvin
2002-08-14 21:11 ` Willy Tarreau
2002-08-14 21:13 ` H. Peter Anvin
2002-08-15 1:23 ` Alan Cox
2002-08-15 1:28 ` H. Peter Anvin
2002-08-15 1:37 ` Alan Cox
2002-08-14 22:53 ` David Lang
2002-08-14 23:31 ` Jamie Lokier
2002-08-15 6:44 ` Willy Tarreau
2002-08-15 6:55 ` H. Peter Anvin
[not found] <3D56147E.15E7A98@zip.com.au.suse.lists.linux.kernel>
2002-08-11 9:53 ` Andi Kleen
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