linux-kernel - Dynticks Causing High Context Switch Rate in ksoftirqd

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Message-ID: <46738.67.173.156.207.1196304247.squirrel@www.techfinesse.net>
Date:	Wed, 28 Nov 2007 20:44:07 -0600 (CST)
From:	bdupree@...hfinesse.com
To:	linux-kernel@...r.kernel.org
Subject: Dynticks Causing High Context Switch Rate in ksoftirqd

I built the same dynticks-enabled 2.6.23.9 kernel on a nearly identical
system with minor changes to reflect the slightly different hardware.
These two systems have identical MSI E7210 MasterX FA6R motherboards (same
model and revision.) The differences are as follows:

behemoth (using Slackware 10.2)
-----------------------------------------------------------------
dual 2.4 GHz Xeons 400 MHz FSB
LSI 53c1030 PCI-X Fusion-MPT Dual Ultra320 SCSI
Newer SATA/PATA Intel PIIX drivers

titan (using Slackware 11.0)
-----------------------------------------------------------------
dual 2.0 GHz Xeons 533 MHz FSB
Creative Labs SB Audigy LS (using ALSA driver)
Older IDE PATA Intel PIIX drivers

The result is that "behemoth" continues to exhibit 155,000 context
switches per second at idle while "titan" shows about 25 - 30 context
switches per second. Note that motherboard BIOS'es are at the same
revision and configured identically.

I guess (ugh) it's time for me to pull the MPT-Fusion U320 HBA and the
SATA disks out of "behemoth" and configure it with old style IDE drives to
be as close as possible to "titan." Then I can add parts back and see when
the problem occurs.

Best regards,

--Bill DuPree

P.S. See attachment for config details and other data.

View attachment "config_info.txt" of type "text/plain" (163821 bytes)