Messages in this thread | | | Date | Sat, 27 Feb 2010 10:52:09 +0100 | Subject | schedule (wait_event) vs. while | From | Rafał Miłecki <> |
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In radeon engine reclocking code I need to do some calculations and then wait for VBLANK interrupt. Right after VBLANK interrupt will happen I need to reclock ASAP.
Interrupts are received by another context and I need some quite fast synchronization.
1) Schedule solution: reclocking() { calculations(); radeon->vblank_sync = 0; wait_event_timeout(radeon->wq, radeon->vblank_sync, timeout); reclock(); } i-handler() { radeon->vblank_sync = 1; }
2) While solution: reclocking() { calculations(); del_timer(radeon->fake_vblank); radeon->vblank_sync = 0; mod_timer(radeon->fake_vblank, 10ms); while(!radeon->vblank_sync); reclock(); } i-handler() { radeon->vblank_sync = 1; } fake-handler() { radeon->vblank_sync = 1; }
Of course first one is much cleaner but internally wait_event_timeout uses schedule_timeout(). Now according to LDD3: > Once a process releases the processor with schedule, there are no guarantees that the process will get the processor back anytime soon. Therefore, calling schedule in this manner is not a safe solution to the driver’s needs, in addition to being bad for the computing system as a whole. If you test jitsched while running load50, you can see that the delay associated to each line is extended by a few seconds, because other processes are using the CPU when the timeout expires.
I can not afford any delays because VBLANK is so short timeframe. Is there any better solution?
-- Rafał -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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