From: Shaohua Li <shaohua.li@intel.com>
To: Tejun Heo <tj@kernel.org>
Cc: lkml <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
"cl@linux.com" <cl@linux.com>
Subject: Re: [PATCH 3/4]percpu_counter: fix code for 32bit systems
Date: Wed, 13 Apr 2011 09:05:36 +0800 [thread overview]
Message-ID: <1302656736.3981.138.camel@sli10-conroe> (raw)
In-Reply-To: <20110412190251.GD16342@mtj.dyndns.org>
On Wed, 2011-04-13 at 03:02 +0800, Tejun Heo wrote:
> On Tue, Apr 12, 2011 at 04:04:04PM +0800, Shaohua Li wrote:
> > static inline s64 percpu_counter_read(struct percpu_counter *fbc)
> > {
> > +#if BITS_PER_LONG == 32
> > + s64 count;
> > + spin_lock(&fbc->lock);
> > + count = fbc->count;
> > + spin_unlock(&fbc->lock);
> > + return count;
> > +#else
> > return fbc->count;
> > +#endif
>
> I don't know. Is there any problem caused by this? The interface is
> known to be unreliable and already being used in speculative manner.
> I think it's more beneficial to avoid using locks on fast read path.
yes, it is unreliable, but only in an extent of batch*nr_cpus. accessing
64bits in 32bit machine can give us a _very_ big inaccuracy, which is
unacceptable to me.
prev parent reply other threads:[~2011-04-13 1:05 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-12 8:04 Shaohua Li
2011-04-12 9:03 ` Eric Dumazet
2011-04-13 1:01 ` Shaohua Li
2011-04-13 2:32 ` Eric Dumazet
2011-04-13 2:41 ` Shaohua Li
2011-04-13 2:47 ` Eric Dumazet
2011-04-13 3:03 ` Shaohua Li
2011-04-13 3:50 ` tj
2011-04-13 4:37 ` Shaohua Li
2011-04-13 3:53 ` Eric Dumazet
2011-04-13 4:00 ` tj
2011-04-12 19:02 ` Tejun Heo
2011-04-13 1:05 ` Shaohua Li [this message]
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