linux-kernel - Re: lots of brief rcu stalls.

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Message-ID: <20131205173102.GS15492@linux.vnet.ibm.com>
Date:	Thu, 5 Dec 2013 09:31:02 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: lots of brief rcu stalls.

On Thu, Dec 05, 2013 at 12:15:50PM -0500, Dave Jones wrote:
> On Thu, Dec 05, 2013 at 08:49:12AM -0800, Paul E. McKenney wrote:
> 
>  > But what workload are you running that causes this?  The only way I
>  > can think of to make this happen requires that you have at least one
>  > CPU spending more than 21 seconds running continuously in kernel mode.
>  > Is that what you are doing, or have you come up with some other creative
>  > way for this to happen?  In the latter case, I would really like to know
>  > about it in case it exposes yet another flaw in my RCU design.  ;-)
> 
> just the regular trinity runs, so it could be anything.
> (Running a few instances of it, with a couple dozen child processes each to drive up the loadavg)

Well, trinity has caused kernel-mode execution periods in excess of
21 seconds in the past, so I will assume that this is the cause until
further notice.

> if only I had a trace or something that I could start to guess at what was happening :)

Maybe creating such a trace would expose additional bugs.  ;-)

							Thanx, Paul

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