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Stephane asked about PERF_COUNT_SW_CPU_MIGRATIONS and I realized it was borken: > The problem is that the task isn't actually scheduled while its being > migrated (obviously), and if its not scheduled, the counters aren't > scheduled either, so there's no observing of the fact. > > A further problem with migrations is that many migrations happen from > softirq context, which is nested inside the 'random' task context of > whoemever happens to run at that time, similarly for the wakeup > migrations triggered from (soft)irq context. All those end up being > accounted in the task that's currently running, eg. your 'ls'. The below cures this by marking a task as migrated and accounting it on the subsequent sched_in(). Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Borislav Petkov <bp@alien8.de> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephane Eranian <eranian@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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