From: Tejun Heo <tj@kernel.org>
To: Shaohua Li <shaohua.li@intel.com>
Cc: lkml <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
"cl@linux.com" <cl@linux.com>
Subject: Re: [PATCH 1/4]percpu_counter: make API return consistent value
Date: Wed, 13 Apr 2011 12:08:31 +0900 [thread overview]
Message-ID: <20110413030831.GG16342@mtj.dyndns.org> (raw)
In-Reply-To: <1302657855.3981.153.camel@sli10-conroe>
Hello,
On Wed, Apr 13, 2011 at 09:24:15AM +0800, Shaohua Li wrote:
> > Ummm, on UP, the counters cannot be positive.
> s/positive/negative?
Yeap.
> > The _positive interface
> > is there to make it easier to cope with deviations introduced by
> > unsynchronized modifications by different CPUs. On UP, such
> > deviations don't happen at all so _positive interface is the same as
> > the counterpart without the postfix.
> I'm confused. the counter could be negative, we have *_dec, *_sub.
Yes it can technically but I was referring to the intent of the API.
The whole percpu counter is supposed to track a positive number. The
_positive interface is there just to cope with deviations caused by
distribution over multiple per-cpu counters, which can't happen on UP.
When the counter can actually be negative, the API doesn't make whole
lot of sense. I agree it's poorly documented.
Thanks.
--
tejun
prev parent reply other threads:[~2011-04-13 3:08 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-12 8:03 [PATCH 1/4]percpu_counter: make API return consistent value Shaohua Li
2011-04-12 18:49 ` Tejun Heo
2011-04-13 1:24 ` Shaohua Li
2011-04-13 3:08 ` Tejun Heo [this message]
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