Horton

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

Josh Berkus <josh@agliodbs.com>

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From: Josh Berkus <josh@agliodbs.com>
To: Tom Lane <tgl@sss.pgh.pa.us>, pg@fastcrypt.com
Cc: Paul Tuckfield <paul@tuckfield.com>, Anjan Dave <adave@vantage.com>, Neil Conway <neilc@samurai.com>, Dirk Lutzebäck <lutzeb@aeccom.com>, pgsql-performance@postgresql.org
Date: 2004-04-22T02:53:24Z
Lists: pgsql-performance 
Tom,

> As far as I can tell, this does reduce the rate of semop's
> significantly, but it does so by bringing the overall processing rate
> to a crawl :-(.  I see 97% CPU idle time when using this patch.
> I believe what is happening is that the select() delay in s_lock.c is
> being hit frequently because the spin loop isn't allowed to run long
> enough to let the other processor get out of the spinlock.

Also, I tested it on production data, and it reduces the CSes by about 40%.  
An improvement, but not a magic bullet.

-- 
Josh Berkus
Aglio Database Solutions
San Francisco