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Date: Wed, 1 Dec 2010 15:37:04 +0100 From: Harry Nak <harrynak@...il.com> To: linux-kernel@...r.kernel.org Subject: timer.c - high load avarage with idle cpu Hi all, I am developing an application on a at91rm9200 platform. Recently I found out that the load average on this system is very high while the cpu remains almost idle. My application uses a lot of timers but the expiration of such a timer causes almost no processing to be performed. I think I found the reason for this load average/cpu usage inconsistency and I (think I ) found a solution: update_process_times() in timer.c first calls the function run_local_timers() before calling scheduler_tick(). run_local_timers() raises TIMER_SOFTIRQ, which causes threads associated with any expired timers to be marked RUNNABLE. scheduler_tick() -> update_cpu_load() -> calc_load_account_active() -> calc_load_fold_active() adds such a thread to the number of active threads, thus causing the load average to increase. However this particular thread never had to wait to become running and it will not consume much cpu time. My solution is to postpone the call to run_local_timers() until scheduler_tick() has been called. Could anybody confirm my theory and is it possible that my solution breaks anything? - Harry -- 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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