From: Gilad Ben-Yossef <gilad@benyossef.com>
To: Avi Kivity <avi@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>,
linux-kernel@vger.kernel.org, Chris Metcalf <cmetcalf@tilera.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Frederic Weisbecker <fweisbec@gmail.com>,
Russell King <linux@arm.linux.org.uk>,
linux-mm@kvack.org, Matt Mackall <mpm@selenic.com>,
Sasha Levin <levinsasha928@gmail.com>,
Rik van Riel <riel@redhat.com>, Andi Kleen <andi@firstfloor.org>,
apkm@linux-foundation.org
Subject: Re: [PATCH v4 4/5] slub: Only IPI CPUs that have per cpu obj to flush
Date: Mon, 2 Jan 2012 13:59:30 +0200 [thread overview]
Message-ID: <CAOtvUMfWKpXaR6Ph1ZN6g0QhgmZtbcf=hMSgtkD-1pLpkzSuNA@mail.gmail.com> (raw)
In-Reply-To: <4F008ECA.5040703@redhat.com>
On Sun, Jan 1, 2012 at 6:50 PM, Avi Kivity <avi@redhat.com> wrote:
> 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.
>
Right, I was only thinking on my own uses, which are O(NR_CPUS) by nature.
I wonder if it would be better to create a safe_cpumask_var type with
its own alloc function
free and and sset_cpu function but no clear_cpu function so that the
compiler will catch
cases of trying to clear bits off of such a cpumask?
It seems safer and also makes handling the free function easier.
Does that makes sense or am I over engineering it? :-)
Gilad
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next prev parent reply other threads:[~2012-01-02 11:59 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-22 11:08 [PATCH v4 0/5] Reduce cross CPU IPI interference Gilad Ben-Yossef
2011-11-22 11:08 ` [PATCH v4 1/5] smp: Introduce a generic on_each_cpu_mask function Gilad Ben-Yossef
2011-11-22 11:08 ` [PATCH v4 2/5] arm: Move arm over to generic on_each_cpu_mask Gilad Ben-Yossef
2011-11-22 21:00 ` Russell King - ARM Linux
2011-11-23 6:47 ` Gilad Ben-Yossef
2011-11-22 11:08 ` [PATCH v4 3/5] tile: Move tile to use " Gilad Ben-Yossef
2011-11-22 11:08 ` [PATCH v4 4/5] slub: Only IPI CPUs that have per cpu obj to flush Gilad Ben-Yossef
2011-11-23 6:23 ` Pekka Enberg
2011-11-23 6:57 ` Pekka Enberg
2011-11-23 7:52 ` Gilad Ben-Yossef
2012-01-01 12:41 ` Avi Kivity
2012-01-01 16:12 ` Gilad Ben-Yossef
2012-01-01 16:50 ` Avi Kivity
2012-01-02 11:59 ` Gilad Ben-Yossef [this message]
2012-01-02 13:30 ` Avi Kivity
2012-01-08 16:13 ` Gilad Ben-Yossef
2012-01-08 16:15 ` Avi Kivity
2011-11-22 11:08 ` [PATCH v4 5/5] mm: Only IPI CPUs to drain local pages if they exist Gilad Ben-Yossef
2011-11-23 7:45 ` Pekka Enberg
2011-12-23 10:28 ` Mel Gorman
2011-12-25 9:39 ` Gilad Ben-Yossef
2011-12-30 15:04 ` Mel Gorman
2011-12-30 15:25 ` Chris Metcalf
2011-12-30 16:08 ` Mel Gorman
2011-12-30 20:29 ` Gilad Ben-Yossef
2012-01-01 8:03 ` Gilad Ben-Yossef
2011-12-30 20:16 ` Gilad Ben-Yossef
2011-11-23 1:36 ` [PATCH v4 0/5] Reduce cross CPU IPI interference Chris Metcalf
2011-11-23 6:52 ` Gilad Ben-Yossef
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