Date: Tue, 20 Dec 2005 05:24:42 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Lee Revell <rlrevell@joe-job.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       "Paul E. McKenney" <paulmck@us.ibm.com>
Subject: Re: 2.6.14-rt22 (and mainline) excessive latency
Message-ID: <20051220042442.GA32039@elte.hu>
References: <1135039244.28649.41.camel@mindpipe>
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* Lee Revell <rlrevell@joe-job.com> wrote:

> I captured this 3+ ms latency trace when killing a process with a few 
> thousand threads.  Can a cond_resched be added to this code path?

>     bash-17992 0.n.1   29us : eligible_child (do_wait)
> 
>     [ 3000+ of these deleted ]
> 
>     bash-17992 0.n.1 3296us : eligible_child (do_wait)

Atomicity of signal delivery is pretty much a must, so i'm not sure this 
particular latency can be fixed, short of running PREEMPT_RT. Paul E.  
McKenney is doing some excellent stuff by RCU-ifying the task lookup and 
signal code, but i'm not sure whether it could cover do_wait().

	Ingo
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