linux-kernel - serial percpu_ref draining in exit

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Message-ID: <20150319173413.GU25365@htj.duckdns.org>
Date:	Thu, 19 Mar 2015 13:34:13 -0400
From:	Tejun Heo <tj@...nel.org>
To:	kent.overstreet@...il.com, Benjamin LaHaise <bcrl@...ck.org>
Cc:	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Subject: serial percpu_ref draining in exit_aio()

Hello,

So, Jens noticed that fio process exiting takes seconds when there are
multiple aio contexts and the culprit seems to be the serial
percpu_ref draining in exit_aio().  It's generally a bad idea to
expose RCU latencies to userland because they add up really quickly
and are unrelated to other performance parameters.  Can you guys
please at least update the code so that it waits for all percpu_refs
to drain at the same time rather than one after another?  That should
resolve the worst part of the problem.

Thanks.

-- 
tejun
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