linux-kernel - Re: [patch 4/4] blk-mq: switch to percpu-ida for tag menagement

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Date:	Fri, 11 Oct 2013 08:28:54 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Shaohua Li <shli@...nel.org>, linux-kernel@...r.kernel.org
CC:	kmo@...erainc.com
Subject: Re: [patch 4/4] blk-mq: switch to percpu-ida for tag menagement

On 10/11/2013 01:18 AM, Shaohua Li wrote:
> Using percpu-ida to manage blk-mq tags. the percpu-ida has similar algorithm
> like the blk-mq-tag. The difference is when a cpu can't allocate tags
> blk-mq-tag uses ipi to purge remote cpu cache and percpu-ida directly purges
> remote cpu cache. In practice (testing null_blk), the percpu-ida approach is
> much faster when total tags aren't enough.

I'm not surprised it's a lot faster the the pathological case of needing
to prune tags, the IPI isn't near ideal for that. I'm assuming the
general performance is the same for the non-full case?

-- 
Jens Axboe

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