linux-kernel - Re: [PATCHSET x86/core/percpu] improve the first percpu chunk allocation

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Date:	Wed, 4 Mar 2009 01:50:36 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>, Tejun Heo <tj@...nel.org>,
	tglx@...utronix.de, x86@...nel.org, linux-kernel@...r.kernel.org,
	jeremy@...p.org, cpw@....com, nickpiggin@...oo.com.au,
	ink@...assic.park.msu.ru
Subject: Re: [PATCHSET x86/core/percpu] improve the first percpu  chunk
	allocation


* H. Peter Anvin <hpa@...or.com> wrote:

> Rusty Russell wrote:
>> On Wednesday 25 February 2009 01:07:24 Tejun Heo wrote:
>>> it always
>>> saves a 2MB TLB entry for all the non-NUMA machines out there.
>>
>> Note that everyone keeps talking about "a" TLB entry; I wanted to make
>> sure (esp. for those of us reading from the sidelines), it's not: it's
>> up to num_possible_cpus() TLB entries.  Of course, many paths won't access
>> other CPU's data, but it'd be interesting (and pretty easy) to actually
>> instrument how rare this is...
>>
>
> Actually it's up to the number of actual CPUs in the system... 
> obviously there isn't any data allocated for non-present CPUs.

well, we allocate percpu data for each possible CPU.

In the overwhelming majority of cases that means all actual 
CPUs.

	Ingo
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