From: Adrian Bunk <bunk@stusta.de>
To: Tim Schmielau <tim@physik3.uni-rostock.de>
Cc: Linus Torvalds <torvalds@osdl.org>, linux-kernel@vger.kernel.org
Subject: Re: please pull from the trivial tree
Date: Fri, 1 Dec 2006 13:55:04 +0100 [thread overview]
Message-ID: <20061201125504.GC11084@stusta.de> (raw)
In-Reply-To: <Pine.LNX.4.63.0612011329130.3090@fink.physik3.uni-rostock.de>
On Fri, Dec 01, 2006 at 01:41:18PM +0100, Tim Schmielau wrote:
> > Chase Venters (1):
> > Fix jiffies.h comment
>
> This one actually obscures the comment rather than fixing it.
>
> >From jiffies.h:
> > 76 /*
> > 77 * The 64-bit value is not volatile - you MUST NOT read it
> > 78 * without sampling the sequence number in xtime_lock.
> > 79 * get_jiffies_64() will do this for you as appropriate.
> > 80 */
> > 81 extern u64 __jiffy_data jiffies_64;
> > 82 extern unsigned long volatile __jiffy_data jiffies;
>
> Note that jiffies is volatile, while jiffies_64 is not; the comment
> currently explains that. The proposed patch
>
> > Fix jiffies.h comment
> > jiffies.h includes a comment informing that jiffies_64 must be read with the
> > assistance of the xtime_lock seqlock. The comment text, however, calls
> > jiffies_64 "not volatile", which should probably read "not atomic".
> >
> > --- a/include/linux/jiffies.h
> > +++ b/include/linux/jiffies.h
> > @@ -74,7 +74,7 @@
> > #define __jiffy_data __attribute__((section(".data")))
> > /*
> > - * The 64-bit value is not volatile - you MUST NOT read it
> > + * The 64-bit value is not atomic - you MUST NOT read it
> > * without sampling the sequence number in xtime_lock.
> > * get_jiffies_64() will do this for you as appropriate.
> > */
>
> would leave a comment that is correct, but less useful (I'd expect any
> kernel hacker to know that u64 is non-atomic on many platforms).
If kernel hackers are expected to already know it's non-atomic we could
remove the whole comment.
The comment regarding "volatile" was bogus since "volatile" wouldn't
help against getting garbage when reading an u64 variable.
> Tim
cu
Adrian
--
"Is there not promise of rain?" Ling Tan asked suddenly out
of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed
next prev parent reply other threads:[~2006-12-01 12:55 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-12-01 11:37 please pull from the trivial tree Adrian Bunk
2006-12-01 12:41 ` Tim Schmielau
2006-12-01 12:55 ` Adrian Bunk [this message]
2006-12-01 13:08 ` Tim Schmielau
-- strict thread matches above, loose matches on Subject: below --
2008-02-03 20:17 Adrian Bunk
2007-07-22 21:08 Adrian Bunk
2007-05-11 17:15 Adrian Bunk
2007-05-09 9:30 Adrian Bunk
2007-02-18 1:12 Adrian Bunk
2006-12-12 23:48 Adrian Bunk
2006-10-03 23:05 Adrian Bunk
2006-06-26 20:26 Adrian Bunk
2006-04-02 14:15 Adrian Bunk
2006-04-01 10:43 Adrian Bunk
2006-03-26 17:31 Adrian Bunk
2006-03-25 10:17 Adrian Bunk
2006-03-22 10:41 Adrian Bunk
2006-01-15 2:05 Adrian Bunk
2006-01-11 1:31 Adrian Bunk
2006-01-10 0:54 Adrian Bunk
2006-01-03 13:19 Adrian Bunk
2005-11-08 16:55 Adrian Bunk
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