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Message-ID: <20110413030831.GG16342@mtj.dyndns.org> Date: Wed, 13 Apr 2011 12:08:31 +0900 From: Tejun Heo <tj@...nel.org> To: Shaohua Li <shaohua.li@...el.com> Cc: lkml <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, "cl@...ux.com" <cl@...ux.com> Subject: Re: [PATCH 1/4]percpu_counter: make API return consistent value 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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