Date: Sat, 03 Sep 2011 14:38:32 -0600 From: Brett Glass <brett@lariat.net> To: questions@freebsd.org Subject: Huge interrupt overhead reported after RAM added to Atom-based system Message-ID: <201109032038.OAA27146@lariat.net>
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I've just seen something very peculiar. I have here a dual Atom (D525) system which was running with 1 GB of RAM, and this morning I put a 4 GB module into the system instead. Suddenly, the systat(8) and top(8) commands were both reporting bursts of interrupt overhead as high as 25% of total CPU capacity. Yet, in the display from the systat -vmstat option, no additional interrupts were appearing on the right hand side of the screen where interrupt sources were listed. The system is running FreeBSD 8.1-RELEASE. The documentation for several motherboards online mention that the Atom can be run with 4 GB of RAM with a "64 bit operating system." I can't tell whether something non-obvious is going on under the hood -- either in the chipset or in the CPUs -- that's racking up overhead, or if the interrupt overhead doesn't exist at all and the reported CPU load is an artifact of some weirdness in the kernel. I need to know, though, before I deploy the system... so I'd appreciate any advice or ideas from any kernel experts who might be reading messages here. --Brett Glass
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