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Date: Fri, 23 Nov 2007 11:46:56 +0100 From: Johannes Berg <johannes@...solutions.net> To: Linux Kernel list <linux-kernel@...r.kernel.org> Cc: linuxppc-dev list <linuxppc-dev@...abs.org> Subject: time accounting problem (powerpc only?) Hi, On my powerbook, with NO_HZ and HIGH_RES_TIMERS, I observed recently that powernowd would not ever switch between CPU speeds. Doing some scripting to read /proc/stat every half second and print the differences, I get output like this on a mostly idle system: # for reference: # [user, nice, system, idle, iowait, irq, softirq, steal, guest] [4, 0, 3, 46, 0, 264, 0, 0, 0] [5, 0, 4, 41, 0, 266, 0, 0, 0] [4, 0, 7, 37, 0, 299, 0, 0, 0] Now starting an empty while (1) loop, I see: [53, 0, 1, 0, 0, 243, 0, 0, 0] [53, 0, 2, 0, 0, 224, 0, 0, 0] [45, 0, 7, 0, 0, 249, 0, 0, 0] As you can see, the "irq" time is very high so that "user" (mostly my CPU burning program) only accounts for maybe 15%. This leads to powernowd thinking that all is fine and no switching is required. Also, the whole stuff leads to top(1) displaying about 80-90% "hi" (hard irq? calculated as irq - softirq?) time. Does anybody have an idea why the irq time is so high? And no, I don't think it can actually be true, I'm seeing maybe 500 interrupts/second (most due to USB). johannes - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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