From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Satyam Sharma <ssatyam@cse.iitk.ac.in>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
David Howells <dhowells@redhat.com>, Andi Kleen <ak@suse.de>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of memory addresses
Date: Wed, 25 Jul 2007 14:54:13 +1000 [thread overview]
Message-ID: <46A6D775.4030802@yahoo.com.au> (raw)
In-Reply-To: <alpine.LFD.0.999.0707241017440.3607@woody.linux-foundation.org>
Linus Torvalds wrote:
>
> On Tue, 24 Jul 2007, Benjamin Herrenschmidt wrote:
>>Besides, as Nick pointed out, it prevents some valid optimizations.
>
>
> No it doesn't. Not the ones on the functions that just do an inline asm.
>
> The only valid optimization it might break is for "constant_test_bit()",
> which isn't even using inline asm.
The constant case is probably most used (at least for page flags), and
is most important for me. constant_test_bit may not be using inline asm,
but the volatile pointer target means that it reloads the value and can't
do much optimisation over it.
BTW. once volatile goes away, i386 really should start using the C
versions of __set_bit and __clear_bit as well IMO. (at least for the
constant bitnr case), so gcc can potentially optimise better.
--
SUSE Labs, Novell Inc.
next prev parent reply other threads:[~2007-07-25 4:54 UTC|newest]
Thread overview: 92+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-07-23 16:05 [PATCH 0/8] i386: bitops: Cleanup, sanitize, optimize Satyam Sharma
2007-07-23 16:05 ` [PATCH 1/8] i386: bitops: Update/correct comments Satyam Sharma
2007-07-23 16:05 ` [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints Satyam Sharma
2007-07-23 16:10 ` Andi Kleen
2007-07-23 16:21 ` Satyam Sharma
2007-07-23 16:30 ` Andi Kleen
2007-07-23 16:36 ` Jan Hubicka
2007-07-23 18:05 ` H. Peter Anvin
2007-07-23 18:28 ` H. Peter Anvin
2007-07-23 17:57 ` Linus Torvalds
2007-07-23 18:14 ` Satyam Sharma
2007-07-23 18:32 ` Andi Kleen
2007-07-23 18:39 ` H. Peter Anvin
2007-07-23 18:52 ` Satyam Sharma
2007-07-23 16:05 ` [PATCH 3/8] i386: bitops: Rectify bogus "+m" constraints Satyam Sharma
2007-07-23 16:37 ` Andi Kleen
2007-07-23 17:15 ` Satyam Sharma
2007-07-23 17:46 ` Linus Torvalds
2007-07-24 9:22 ` David Howells
2007-07-23 16:05 ` [PATCH 4/8] i386: bitops: Kill volatile-casting of memory addresses Satyam Sharma
2007-07-23 17:52 ` Linus Torvalds
2007-07-24 4:19 ` Nick Piggin
2007-07-24 6:23 ` Satyam Sharma
2007-07-24 7:16 ` Nick Piggin
2007-07-24 9:49 ` Benjamin Herrenschmidt
2007-07-24 17:20 ` Linus Torvalds
2007-07-24 17:39 ` Jeff Garzik
2007-07-25 4:54 ` Nick Piggin [this message]
2007-07-23 16:05 ` [PATCH 5/8] i386: bitops: Contain warnings fallout from the death of volatiles Satyam Sharma
2007-07-23 16:05 ` [PATCH 6/8] i386: bitops: Don't mark memory as clobbered unnecessarily Satyam Sharma
2007-07-23 16:13 ` Andi Kleen
2007-07-23 16:26 ` Satyam Sharma
2007-07-23 16:33 ` Andi Kleen
2007-07-23 17:12 ` Satyam Sharma
2007-07-23 17:49 ` Jeremy Fitzhardinge
2007-07-23 17:55 ` Linus Torvalds
2007-07-24 9:52 ` Benjamin Herrenschmidt
2007-07-24 17:24 ` Linus Torvalds
2007-07-24 17:42 ` Trond Myklebust
2007-07-24 18:13 ` Linus Torvalds
2007-07-24 18:28 ` Trond Myklebust
2007-07-24 21:37 ` Benjamin Herrenschmidt
2007-07-24 21:55 ` Trond Myklebust
2007-07-24 22:32 ` Benjamin Herrenschmidt
2007-07-25 4:10 ` Nick Piggin
2007-07-24 21:36 ` Benjamin Herrenschmidt
2007-07-24 3:57 ` Nick Piggin
2007-07-24 6:38 ` Satyam Sharma
2007-07-24 7:24 ` Nick Piggin
2007-07-24 8:29 ` Satyam Sharma
2007-07-24 8:39 ` Nick Piggin
2007-07-24 8:38 ` Trent Piepho
2007-07-24 19:39 ` Linus Torvalds
2007-07-24 20:37 ` Andi Kleen
2007-07-24 20:08 ` Linus Torvalds
2007-07-24 21:31 ` Jeremy Fitzhardinge
2007-07-24 21:46 ` Linus Torvalds
2007-07-26 1:07 ` Trent Piepho
2007-07-26 1:18 ` Linus Torvalds
2007-07-26 1:22 ` Linus Torvalds
2007-07-24 9:44 ` David Howells
2007-07-24 10:02 ` Satyam Sharma
2007-07-23 16:06 ` [PATCH 7/8] i386: bitops: Kill needless usage of __asm__ __volatile__ Satyam Sharma
2007-07-23 16:18 ` Andi Kleen
2007-07-23 16:22 ` [PATCH 7/8] i386: bitops: Kill needless usage of __asm__ __volatile__ II Andi Kleen
2007-07-23 16:32 ` [PATCH 7/8] i386: bitops: Kill needless usage of __asm__ __volatile__ Satyam Sharma
2007-07-23 16:23 ` Jeremy Fitzhardinge
2007-07-23 16:43 ` Satyam Sharma
2007-07-23 17:39 ` Jeremy Fitzhardinge
2007-07-23 18:07 ` Satyam Sharma
2007-07-23 18:28 ` Jeremy Fitzhardinge
2007-07-23 20:29 ` Trent Piepho
2007-07-23 20:40 ` Jeremy Fitzhardinge
2007-07-23 21:06 ` Trent Piepho
2007-07-23 21:30 ` Andi Kleen
2007-07-23 21:48 ` Nicholas Miell
2007-07-23 16:06 ` [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clear_bit() definitions Satyam Sharma
2007-07-24 3:53 ` Nick Piggin
2007-07-24 7:34 ` Satyam Sharma
2007-07-24 7:48 ` Jeremy Fitzhardinge
2007-07-24 8:31 ` Nick Piggin
2007-07-24 8:20 ` Nick Piggin
2007-07-24 9:21 ` Satyam Sharma
2007-07-24 10:25 ` Nick Piggin
2007-07-24 11:10 ` Satyam Sharma
2007-07-24 11:32 ` Nick Piggin
2007-07-24 11:45 ` Satyam Sharma
2007-07-24 12:01 ` Nick Piggin
2007-07-24 17:12 ` Linus Torvalds
2007-07-24 19:01 ` Satyam Sharma
2007-07-30 17:57 ` [PATCH 0/8] i386: bitops: Cleanup, sanitize, optimize Denis Vlasenko
2007-07-31 1:07 ` Satyam Sharma
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