Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobbered unnecessarily | KernelTrap

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobbered unnecessarily

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From: Andi Kleen

Subject: Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobbered unnecessarily

Date: Monday, July 23, 2007 - 9:13 am

On Monday 23 July 2007 18:05:58 Satyam Sharma wrote:
quoted text> From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
> 
> [6/8] i386: bitops: Don't mark memory as clobbered unnecessarily
> 
> The goal is to let gcc generate good, beautiful, optimized code.

The first goal is correct code.

The reason for the memory barrier is to prevent other memory references
from being moved over the atomic reference.

e.g. when a bit is used to communicate with another CPU this might be dangerous.

I don't think it's a good idea to remove them. It'll likely introduce subtle
bugs. Atomic bitops tend to be so slow anyways that it doesn't make much
difference.

-Andi

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Messages in current thread:

[PATCH 0/8] i386: bitops: Cleanup, sanitize, optimize, Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 1/8] i386: bitops: Update/correct comments, Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 3/8] i386: bitops: Rectify bogus "+m" constraints, Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 4/8] i386: bitops: Kill volatile-casting of memory ..., Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 5/8] i386: bitops: Contain warnings fallout from th ..., Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 6/8] i386: bitops: Don't mark memory as clobbered u ..., Satyam Sharma, (Mon Jul 23, 9:05 am)

[PATCH 7/8] i386: bitops: Kill needless usage of __asm__ _ ..., Satyam Sharma, (Mon Jul 23, 9:06 am)

[PATCH 8/8] i386: bitops: smp_mb__{before, after}_clear_bi ..., Satyam Sharma, (Mon Jul 23, 9:06 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Andi Kleen, (Mon Jul 23, 9:10 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Andi Kleen, (Mon Jul 23, 9:13 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Andi Kleen, (Mon Jul 23, 9:18 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Satyam Sharma, (Mon Jul 23, 9:21 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Andi Kleen, (Mon Jul 23, 9:22 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Jeremy Fitzhardinge, (Mon Jul 23, 9:23 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Satyam Sharma, (Mon Jul 23, 9:26 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Andi Kleen, (Mon Jul 23, 9:30 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Satyam Sharma, (Mon Jul 23, 9:32 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Andi Kleen, (Mon Jul 23, 9:33 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Jan Hubicka, (Mon Jul 23, 9:36 am)

Re: [PATCH 3/8] i386: bitops: Rectify bogus "+m" constraints, Andi Kleen, (Mon Jul 23, 9:37 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Satyam Sharma, (Mon Jul 23, 9:43 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Satyam Sharma, (Mon Jul 23, 10:12 am)

Re: [PATCH 3/8] i386: bitops: Rectify bogus "+m" constraints, Satyam Sharma, (Mon Jul 23, 10:15 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Jeremy Fitzhardinge, (Mon Jul 23, 10:39 am)

Re: [PATCH 3/8] i386: bitops: Rectify bogus "+m" constraints, Linus Torvalds, (Mon Jul 23, 10:46 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Jeremy Fitzhardinge, (Mon Jul 23, 10:49 am)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Linus Torvalds, (Mon Jul 23, 10:52 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Mon Jul 23, 10:55 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Linus Torvalds, (Mon Jul 23, 10:57 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, H. Peter Anvin, (Mon Jul 23, 11:05 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Satyam Sharma, (Mon Jul 23, 11:07 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Satyam Sharma, (Mon Jul 23, 11:14 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Jeremy Fitzhardinge, (Mon Jul 23, 11:28 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, H. Peter Anvin, (Mon Jul 23, 11:28 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Andi Kleen, (Mon Jul 23, 11:32 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, H. Peter Anvin, (Mon Jul 23, 11:39 am)

Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints, Satyam Sharma, (Mon Jul 23, 11:52 am)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Trent Piepho, (Mon Jul 23, 1:29 pm)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Jeremy Fitzhardinge, (Mon Jul 23, 1:40 pm)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Trent Piepho, (Mon Jul 23, 2:06 pm)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Andi Kleen, (Mon Jul 23, 2:30 pm)

Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm ..., Nicholas Miell, (Mon Jul 23, 2:48 pm)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Nick Piggin, (Mon Jul 23, 8:53 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Nick Piggin, (Mon Jul 23, 8:57 pm)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Nick Piggin, (Mon Jul 23, 9:19 pm)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Satyam Sharma, (Mon Jul 23, 11:23 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Satyam Sharma, (Mon Jul 23, 11:38 pm)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Nick Piggin, (Tue Jul 24, 12:16 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Nick Piggin, (Tue Jul 24, 12:24 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Satyam Sharma, (Tue Jul 24, 12:34 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Jeremy Fitzhardinge, (Tue Jul 24, 12:48 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Nick Piggin, (Tue Jul 24, 1:20 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Satyam Sharma, (Tue Jul 24, 1:29 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Nick Piggin, (Tue Jul 24, 1:31 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Trent Piepho, (Tue Jul 24, 1:38 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Nick Piggin, (Tue Jul 24, 1:39 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Satyam Sharma, (Tue Jul 24, 2:21 am)

Re: [PATCH 3/8] i386: bitops: Rectify bogus "+m" constraints, David Howells, (Tue Jul 24, 2:22 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., David Howells, (Tue Jul 24, 2:44 am)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Benjamin Herrenschmidt, (Tue Jul 24, 2:49 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Benjamin Herrenschmidt, (Tue Jul 24, 2:52 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Satyam Sharma, (Tue Jul 24, 3:02 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Nick Piggin, (Tue Jul 24, 3:25 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Satyam Sharma, (Tue Jul 24, 4:10 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Nick Piggin, (Tue Jul 24, 4:32 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Satyam Sharma, (Tue Jul 24, 4:45 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Nick Piggin, (Tue Jul 24, 5:01 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Linus Torvalds, (Tue Jul 24, 10:12 am)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Linus Torvalds, (Tue Jul 24, 10:20 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Tue Jul 24, 10:24 am)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Jeff Garzik, (Tue Jul 24, 10:39 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Trond Myklebust, (Tue Jul 24, 10:42 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Tue Jul 24, 11:13 am)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Trond Myklebust, (Tue Jul 24, 11:28 am)

Re: [PATCH 8/8] i386: bitops: smp_mb__{before, after}_clea ..., Satyam Sharma, (Tue Jul 24, 12:01 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Tue Jul 24, 12:39 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Tue Jul 24, 1:08 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Andi Kleen, (Tue Jul 24, 1:37 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Jeremy Fitzhardinge, (Tue Jul 24, 2:31 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Benjamin Herrenschmidt, (Tue Jul 24, 2:36 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Benjamin Herrenschmidt, (Tue Jul 24, 2:37 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Tue Jul 24, 2:46 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Trond Myklebust, (Tue Jul 24, 2:55 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Benjamin Herrenschmidt, (Tue Jul 24, 3:32 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Nick Piggin, (Tue Jul 24, 9:10 pm)

Re: [PATCH 4/8] i386: bitops: Kill volatile-casting of mem ..., Nick Piggin, (Tue Jul 24, 9:54 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Trent Piepho, (Wed Jul 25, 6:07 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Wed Jul 25, 6:18 pm)

Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobber ..., Linus Torvalds, (Wed Jul 25, 6:22 pm)

Re: [PATCH 0/8] i386: bitops: Cleanup, sanitize, optimize