Messages in this thread | | | Date | Wed, 28 Jan 2015 23:18:34 +0800 | Subject | Re: [PATCH 3/5] sched/deadline: Fix wrong cpudl_find() in check_preempt_equal_dl() | From | Xunlei Pang <> |
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Hi Peter,
On 28 January 2015 at 00:47, Peter Zijlstra <peterz@infradead.org> wrote: > On Mon, Jan 19, 2015 at 04:49:38AM +0000, Xunlei Pang wrote: >> In check_preempt_equal_dl(), cpudl_find() is called with a NULL >> later_mask, thus cpudl_find() here doesn't check cpudl::free_cpus >> at all. >> >> This patch takles this issue by always passing a non-NULL later_mask >> to cpudl_find(), thereby fixing this issue. > > Fix what issue? Afaict this is an optimization not a fix.
Currently, check_preempt_equal_dl() invokes cpudl_find() with a NULL mask, so cpudl_find() won't check cpudl::free_cpus. For example, 4 core system, CPU0~CPU2 are all idle(free of deadline tasks), a deadline task is woken on CPU3 which already has one running deadline task with the same deadline value, then cpudl_find() will fail causing CPU3 holding 2 deadline tasks while other cpus are idle, obviously it should be placed on one idle cpu.
Thanks, Xunlei
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