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Subject: Re: RCU latency regression in 2.6.16-rc1
From: Lee Revell <rlrevell@joe-job.com>
To: paulmck@us.ibm.com
Cc: dipankar@in.ibm.com, Ingo Molnar <mingo@elte.hu>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       Linus Torvalds <torvalds@osdl.org>
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Date: Fri, 27 Jan 2006 13:55:22 -0500
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On Thu, 2006-01-26 at 11:18 -0800, Paul E. McKenney wrote:
> >     Xorg-2154  0d.s.  213us : call_rcu_bh (rt_run_flush)
> >     Xorg-2154  0d.s.  215us : local_bh_enable (rt_run_flush)
> >     Xorg-2154  0d.s.  216us : local_bh_enable (rt_run_flush)
> >     Xorg-2154  0d.s.  217us : local_bh_enable (rt_run_flush)
> >     Xorg-2154  0d.s.  218us : local_bh_enable (rt_run_flush)
> >     Xorg-2154  0d.s.  219us : local_bh_enable (rt_run_flush)
> >     Xorg-2154  0d.s.  220us : local_bh_enable (rt_run_flush)
> >     Xorg-2154  0d.s.  222us : local_bh_enable (rt_run_flush)
> >     Xorg-2154  0d.s.  223us : call_rcu_bh (rt_run_flush)
> > 
> > [ zillions of these deleted ]
> > 
> >     Xorg-2154  0d.s. 7335us : local_bh_enable (rt_run_flush)
> 
> Dipankar's latest patch should hopefully address this problem.
> 
> Could you please give it a spin when you get a chance? 

Nope, no improvement at all, furthermore, the machine locked up once
under heavy disk activity.

I just got an 8ms+ latency from rt_run_flush that looks basically
identical to the above.  It's still flushing routes in huge batches:

$ grep 'call_rcu_bh (rt_run_flush)' /proc/latency_trace | wc -l
2738

Lee