linux-kernel - Re: High lock spin time for zone->lru

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Message-ID: <45A89008.2030408@yahoo.com.au>
Date:	Sat, 13 Jan 2007 18:53:44 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Ravikiran G Thirumalai <kiran@...lex86.org>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andi Kleen <ak@...e.de>, Andrew Morton <akpm@...l.org>,
	"Shai Fultheim (Shai@...lex86.org)" <shai@...lex86.org>,
	pravin b shelar <pravin.shelar@...softinc.com>
Subject: Re: High lock spin time for zone->lru_lock under extreme conditions

Ravikiran G Thirumalai wrote:
> On Sat, Jan 13, 2007 at 03:39:45PM +1100, Nick Piggin wrote:

>>What is the "CS time"?
> 
> 
> Critical Section :).  This is the maximal time interval I measured  from 
> t2 above to the time point we release the spin lock.  This is the hold 
> time I guess.
> 
> 
>>It would be interesting to know how long the maximal lru_lock *hold* time 
>>is,
>>which could give us a better indication of whether it is a hardware problem.
>>
>>For example, if the maximum hold time is 10ms, that it might indicate a
>>hardware fairness problem.
> 
> 
> The maximal hold time was about 3s.

Well then it doesn't seem very surprising that this could cause a 30s wait
time for one CPU in a 16 core system, regardless of fairness.

I guess most of the contention, and the lock hold times are coming from
vmscan? Do you know exactly which critical sections are the culprits?

-- 
SUSE Labs, Novell Inc.
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