linux-ext4 - Re: ext4 dbench performance with CONFIG_PREEMPT

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Message-ID: <87d3y8wrq5.fsf@basil.nowhere.org>
Date:	Fri, 09 Apr 2010 17:49:54 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	john stultz <johnstul@...ibm.com>
Cc:	linux-ext4@...r.kernel.org, Mingming Cao <cmm@...ibm.com>,
	keith maanthey <kmannth@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "Theodore Ts'o" <tytso@....edu>,
	Darren Hart <dvhltc@...ibm.com>, tim.c.chen@...el.com
Subject: Re: ext4 dbench performance with CONFIG_PREEMPT_RT

john stultz <johnstul@...ibm.com> writes:
>
> Further using lockstat I was able to isolate it the contention down to
> the journal j_state_lock, and then adding some lock owner tracking, I
> was able to see that the lock owners were almost always in
> start_this_handle, and jbd2_journal_stop when we saw contention (with
> the freq breakdown being about 55% in jbd2_journal_stop and 45% in
> start_this_handle).

FWIW we've been also seeing this on larger systems without RT.
The journal locks are the number one contention in some workloads.
So it's not just a RT problem.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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