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timer: apply PIT quirk to avoid high cpu load

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Alexander Boettcher 2014-07-02 11:54:43 +02:00 committed by Norman Feske
parent b289273d28
commit edc03489b3
1 changed files with 31 additions and 0 deletions
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31
repos/os/src/drivers/timer/include_pit/platform_timer.h
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@ -179,6 +179,37 @@ class Platform_timer
if (timeout_usec > max_timeout())
timeout_usec = max_timeout();
/*
* XXX Quirk - start
*
* On some x86 platforms, it happens that the system seems to slow
* down dramatically for some unclear reasons so far. When this
* happens, the handling of the timeout queue and reprogramming the
* next timeout takes so long that the timer IRQ will fire
* immediately after acknowledging it. This causes the timer
* service to run on a very high rate, which may utilize the CPU
* close to the maximum. We try to detect this condition by the
* following heuristic and apply this quirk, which programs the
* next timeout later in time - so that it will fire not
* immediately after acknowledging it.
*
* This quirk should be removed as soon as it is clear what
* triggers the phenomenon.
*/
enum { QUIRK_TIMEOUT_US = 2800 };
unsigned long now = curr_time();
asm volatile ("":::"memory");
unsigned long later = curr_time();
unsigned long diff = later - now;
if (diff > QUIRK_TIMEOUT_US) {
timeout_usec = diff * 6 > max_timeout() ? max_timeout() : diff * 6;
PERR("apply timer quirk - diff=%lu, timeout_usec=%lu",
diff, timeout_usec);
}
/* XXX Quirk - end */
_counter_init_value = (PIT_TICKS_PER_MSEC * timeout_usec)/1000;
_set_counter(_counter_init_value);
}