linux-kernel - Re: RCU related performance regression in 3.3

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Date:	Fri, 20 Apr 2012 16:45:47 +0200
From:	Pascal Chapperon <pascal.chapperon@...adoo.fr>
To:	paulmck@...ux.vnet.ibm.com
CC:	Josh Boyer <jwboyer@...hat.com>, linux-kernel@...r.kernel.org,
	kernel-team@...oraproject.org
Subject: Re: RCU related performance regression in 3.3

Le 18/04/2012 17:23, Paul E. McKenney a écrit :
>> systemd is controlling the whole boot process including mount
>> operation (apart root filesystem) and as I can see, uses heavily
>> sockets to do it (not to mention cpu-affinity). It controls also the
>> major part of umount operations. Is it possible that your patch hits
>> a systemd bug ?
>
> Is it possible that systemd is using network operations that include
> synchronize_rcu()?  Then if you did the same operation from the
> command line at runtime, you might not see the slowdown.
>
> Is it possible for you to convince systemd to collect RCU event tracing
> during the slow operation?  RCU event tracing is available under
> /sys/kernel/debug/tracing/rcu.
>
-
Paul, thank you for these suggestions : I'll manage to enable RCU event
tracing immediately after mounting debugfs (systemd permits custom
units). As debugfs is mounted early in the boot sequence, maybe I'll
catch something.

Pascal

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