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5680d8094f
When switching between the unstable and stable variants it is currently possible that clock discontinuities occur. And while these will mostly be 'small', attempt to do better. As observed on my IVB-EP, the sched_clock() is ~1.5s ahead of the ktime_get_ns() based timeline at the point of switchover (sched_clock_init_late()) after SMP bringup. Equally, when the TSC is later found to be unstable -- typically because SMM tries to hide its SMI latencies by mucking with the TSC -- we want to avoid large jumps. Since the clocksource watchdog reports the issue after the fact we cannot exactly fix up time, but since SMI latencies are typically small (~10ns range), the discontinuity is mainly due to drift between sched_clock() and ktime_get_ns() (which on my desktop is ~79s over 24days). I dislike this patch because it adds overhead to the good case in favour of dealing with badness. But given the widespread failure of TSC stability this is worth it. Note that in case the TSC makes drastic jumps after SMP bringup we're still hosed. There's just not much we can do in that case without stupid overhead. If we were to somehow expose tsc_clocksource_reliable (which is hard because this code is also used on ia64 and parisc) we could avoid some of the newly introduced overhead. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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| .. | ||
| auto_group.c | ||
| auto_group.h | ||
| clock.c | ||
| completion.c | ||
| core.c | ||
| cpuacct.c | ||
| cpuacct.h | ||
| cpudeadline.c | ||
| cpudeadline.h | ||
| cpufreq.c | ||
| cpufreq_schedutil.c | ||
| cpupri.c | ||
| cpupri.h | ||
| cputime.c | ||
| deadline.c | ||
| debug.c | ||
| fair.c | ||
| features.h | ||
| idle.c | ||
| idle_task.c | ||
| loadavg.c | ||
| Makefile | ||
| rt.c | ||
| sched.h | ||
| stats.c | ||
| stats.h | ||
| stop_task.c | ||
| swait.c | ||
| wait.c | ||