Messages in this thread | | | Date | Thu, 25 Jun 2009 14:10:49 -0500 | From | Jon Hunter <> | Subject | Re: [PATCH 1/2] Dynamic Tick: Prevent clocksource wrapping during idle |
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Jon Hunter wrote: > Jon Hunter wrote: >> Jon Hunter wrote: >>> + * Calculate the time delta for the next timer event. >>> + * If the time delta exceeds the maximum time delta >>> + * permitted by the current clocksource then adjust >>> + * the time delta accordingly to ensure the >>> + * clocksource does not wrap. >>> + */ >>> + time_delta = tick_period.tv64 * delta_jiffies; >> Thinking about this more, although it is very unlikely, for 64-bit >> machines there is a chance that the above multiply could overflow if >> delta_jiffies is very large. >> >> tick_period.tv64 should always be less than NSEC_PER_SEC and so you >> would need delta_jiffies to be greater than 2^32 to cause overflow. On a >> 32-bit machine an unsigned long will not be greater than 2^32 as it is >> only 32-bits but this would be possible on a 64-bit machines. >> >> So to be safe we should make sure that delta_jiffies is not greater than >> NEXT_TIMER_MAX_DELTA (2^30 - 1) before doing the multiply. If you >> think that this is a valid concern, then I can re-work and re-post. >> Sorry for not catching this before. > > With regard to the above, to ensure that there are no overflows with the > above calculation, I re-worked this patch a little. The below should be > equivalent to the current code, just re-organised a little. Let me know > if this would be acceptable or not.
Hi Thomas, John,
Did you guys have chance to review this? Let me know if you have any further comments/feedback.
Cheers Jon
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