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Date: Fri, 12 Dec 2008 06:11:11 +0100
From: Eric Dumazet <dada1@...mosbay.com>
To: Nick Piggin <nickpiggin@...oo.com.au>
CC: Andrew Morton <akpm@...ux-foundation.org>,
Ingo Molnar <mingo@...e.hu>,
Christoph Hellwig <hch@...radead.org>,
David Miller <davem@...emloft.net>,
"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
"kernel-testers@...r.kernel.org >> Kernel Testers List"
<kernel-testers@...r.kernel.org>, Mike Galbraith <efault@....de>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Linux Netdev List <netdev@...r.kernel.org>,
Christoph Lameter <cl@...ux-foundation.org>,
linux-fsdevel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v3 2/7] fs: Use a percpu_counter to track nr_inodes
Nick Piggin a écrit :
> On Friday 12 December 2008 09:39, Eric Dumazet wrote:
>> Avoids cache line ping pongs between cpus and prepare next patch,
>> because updates of nr_inodes dont need inode_lock anymore.
>>
>> (socket8 bench result : no difference at this point)
>
> Looks good.
>
> But.... If we never actually need fast access to the approximate
> total, (which seems to apply to this and the previous patch) we
> could use something much simpler which does not have the spinlock
> or all this batching stuff that percpu counters have. I'd prefer
> that because it will be faster in a straight line...
Well, using a non batching mode could be real easy, just
call __percpu_counter_add(&counter, inc, 1<<30);
Or define a new percpu_counter_fastadd(&counter, inc);
percpu_counter are nice because handle the CPU hotplug problem,
if we want to use for_each_online_cpu() instead of
for_each_possible_cpu().
>
> (BTW. percpu counters can't be used in interrupt context? That's
> nice.)
>
>
Not sure why you said this.
I would like to have a irqsafe percpu_counter, I was preparing such a
patch because we need it for net-next
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