Messages in this thread | | | From | "Chen, Kenneth W" <> | Subject | RE: Regression seen for patch "sched:dont decrease idle sleep avg" | Date | Thu, 11 May 2006 17:04:11 -0700 |
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Tim Chen writes: > See patch: > http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=e72ff0bb2c163eb13014ba113701bd42dab382fe
Con Kolivas wrote on Monday, May 08, 2006 5:43 PM > This patch corrects a bug in the original code which unintentionally dropped > the priority of tasks that were idle but were already high priority on other > merits. It doesn't further increase the priority.
This got me to take a non-casual look at that particular git commit. The first portion of the change log description says perfectly about the intent, but after studying the code, I have to say that the actual code does not implement what people say it will do. In recalc_task_prio(), if a task's sleep_time is more than INTERACTIVE_SLEEP, it will bump up p->sleep_avg all the way to near maximum (at MAX_SLEEP_AVG - DEF_TIMESLICE), which according to my calculation, it will have a priority bonus of 4 (out of max 5).
IOW, for a prolonged sleep, a task will immediately get near maximum priority boost. Is that what the real intent is? Seems to be on the contrary to what the source code comments as well.
I think in the if (sleep_time > INTERACTIVE_SLEEP) block, p->sleep_avg should be treated similarly like what the "else" block is doing: scale it proportionally with past sleep time, perhaps not the immediate previously prolonged sleep because that would for sure bump up priority too fast. A better method might be p->sleep_avg *= 2 or something like that.
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