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Date: Sat, 02 Feb 2008 23:41:51 +0100
From: Kris Kennaway <kris@FreeBSD.org>
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To: Alexander Motin <mav@FreeBSD.org>
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Cc: freebsd-hackers@freebsd.org, freebsd-performance@freebsd.org,
	Robert Watson <rwatson@FreeBSD.org>, Julian Elischer <julian@elischer.org>
Subject: Re: Memory allocation performance
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Alexander Motin wrote:
> Robert Watson wrote:
>> Hence my request for drilling down a bit on profiling -- the question 
>> I'm asking is whether profiling shows things running or taking time 
>> that shouldn't be.
> 
> I have not yet understood why does it happend, but hwpmc shows huge 
> amount of "p4-resource-stall"s in UMA functions:

> For this moment I have invent two possible explanation. One is that due 
> to UMA's cyclic block allocation order it does not fits CPU caches and 
> another that it is somehow related to critical_exit(), which possibly 
> can cause context switch. Does anybody have better explanation how such 
> small and simple in this part function can cause such results?

You can look at the raw output from pmcstat, which is a collection of 
instruction pointers that you can feed to e.g. addr2line to find out 
exactly where in those functions the events are occurring.  This will 
often help to track down the precise causes.

Kris