linux-kernel - Re: [PATCH v4 4/5] slub: Only IPI CPUs that have per cpu obj to flush

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Date:	Sun, 01 Jan 2012 18:50:18 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
CC:	Pekka Enberg <penberg@...nel.org>, linux-kernel@...r.kernel.org,
	Chris Metcalf <cmetcalf@...era.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Russell King <linux@....linux.org.uk>, linux-mm@...ck.org,
	Matt Mackall <mpm@...enic.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, apkm@...ux-foundation.org
Subject: Re: [PATCH v4 4/5] slub: Only IPI CPUs that have per cpu obj to flush

On 01/01/2012 06:12 PM, Gilad Ben-Yossef wrote:
> >
> > Since this seems to be a common pattern, how about:
> >
> >   zalloc_cpumask_var_or_all_online_cpus(&cpus, GFTP_ATOMIC);
> >   ...
> >   free_cpumask_var(cpus);
> >
> > The long-named function at the top of the block either returns a newly
> > allocated zeroed cpumask, or a static cpumask with all online cpus set.
> > The code in the middle is only allowed to set bits in the cpumask
> > (should be the common usage).  free_cpumask_var() needs to check whether
> > the freed object is the static variable.
>
> Thanks for the feedback and advice! I totally agree the repeating
> pattern needs abstracting.
>
> I ended up chosing to try a different abstraction though - basically a wrapper
> on_each_cpu_cond that gets a predicate function to run per CPU to
> build the mask
> to send the IPI to. It seems cleaner to me not having to mess with
> free_cpumask_var
> and it abstracts more of the general pattern.
>

This converts the algorithm to O(NR_CPUS) from a potentially lower
complexity algorithm.  Also, the existing algorithm may not like to be
driven by cpu number.  Both are true for kvm.

-- 
error compiling committee.c: too many arguments to function

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