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Re: Wierd context-switching issue on Xeon patch for 7.4.1

From: Dave Cramer <pg(at)fastcrypt(dot)com>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Wierd context-switching issue on Xeon patch for 7.4.1
Date: 2004-04-27 18:27:33
Message-ID: 1083090452.14759.224.camel@localhost.localdomain (view raw or flat)
Thread:
Lists: pgsql-performance
Josh,

I think you can safely increase by orders of magnitude here, instead of
by +100, my wild ass guess is that the sweet spot is the spin time
should be approximately the time it takes to consume the resource. So if
you have a really fast machine then the spin count should be higher. 

Also you have to take into consideration your memory bus speed, with the
pause instruction inserted in the loop the timing is now dependent on
memory speed.

But... you need a baseline first.

Dave
On Tue, 2004-04-27 at 14:05, Josh Berkus wrote:
> Dave,
> 
> > Are you testing this with Tom's code, you need to do a baseline
> > measurement with 10 and then increase it, you will still get lots of cs,
> > but it will be less.
> 
> No, that was just a test of 1000 straight up.    Tom outlined a method, but I 
> didn't see any code that would help me find a better level, other than just 
> trying each +100 increase one at a time.   This would take days of testing 
> ...
-- 
Dave Cramer
519 939 0336
ICQ # 14675561


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Subject: Re: Wierd context-switching issue on Xeon patch for 7.4.1
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