linux-kernel - Re: [PATCH 1/2] Make the batch size of the percpu

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Message-ID: <1367344522.27102.184.camel@schen9-DESK>
Date:	Tue, 30 Apr 2013 10:55:22 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Al Viro <viro@...iv.linux.org.uk>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <ak@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH 1/2] Make the batch size of the percpu_counter
 configurable

On Tue, 2013-04-30 at 17:53 +0000, Christoph Lameter wrote:
> On Tue, 30 Apr 2013, Tim Chen wrote:
> 
> > > And why is it a pointer?
> >
> > A pointer because the default percpu_counter_batch value could change
> > later when cpus come online after we initialize per cpu counter and
> > percpu_counter_batch will get computed again in percpu_counter_startup.
> > Making it a pointer will make it unnecessary to come back and change the
> > batch sizes if we use static batch value and default batch size.
> 
> But you will have to dereference the pointer whenever you want the batch
> size from the hot path. Looks like it would be better to put the value
> there directly. You have a list of percpu counters that can be traversed
> to change the batch size.
> 

I have considered that.  But the list is not available unless we have
CONFIG_HOTPLUG_CPU compiled in.

Tim


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