linux-kernel - Re: [PATCH 04/10] idr: Percpu ida

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Message-ID: <000001405a4b39ef-0715410a-5061-41e9-9414-86559f16570d-000000@email.amazonses.com>
Date:	Wed, 7 Aug 2013 19:40:15 +0000
From:	Christoph Lameter <cl@...two.org>
To:	Kent Overstreet <kmo@...erainc.com>
cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, Jens Axboe <axboe@...nel.dk>,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Subject: Re: [PATCH 04/10] idr: Percpu ida

On Wed, 7 Aug 2013, Kent Overstreet wrote:

> I was breaking it apart because I was using this_cpu elsewhere too - for
> the bitmap of which cpus have non empty freelists.

this_cpu can be retrieved with smp_processor_id().

> Or is this_cpu_ptr() doing something smarter than per_cpu_ptr(ptr,
> smp_processer_id())? There's so many variants I'm not 100% sure they're
> the same.

Yes it is. It uses a sepecial register that contains the offset of this
cpus per cpu area instead of going through the table of all processor
offsets. Its less code.

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