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62188451f0
We scale stime, utime values based on rtime (sum_exec_runtime converted to jiffies). During scaling we multiple rtime * utime, which seems to be fine, since both values are converted to u64, but it's not. Let assume HZ is 1000 - 1ms tick. Process consist of 64 threads, run for 1 day, threads utilize 100% cpu on user space. Machine has 64 cpus. Process rtime = utime will be 64 * 24 * 60 * 60 * 1000 jiffies, which is 0x149970000. Multiplication rtime * utime result is 0x1a855771100000000, which can not be covered in 64 bits. Result of overflow is stall of utime values visible in user space (prev_utime in kernel), even if application still consume lot of CPU time. A solution to solve this is to perform the multiplication on stime instead of utime. It's easy to grow the utime value fast with a CPU bound thread in userspace for example. Now we assume that doing so with stime is much harder. In most cases a task shouldn't ever spend much time in kernel space as it tends to sleep waiting for jobs completion when they take long to achieve. IO is the typical example of that. Hence scaling the cputime by performing the multiplication on stime instead of utime should considerably reduce the chances of an overflow on most workloads. This is largely inspired by a patch from Stanislaw Gruszka: http://lkml.kernel.org/r/20130107113144.GA7544@redhat.com Inspired-by: Stanislaw Gruszka <sgruszka@redhat.com> Reported-by: Stanislaw Gruszka <sgruszka@redhat.com> Acked-by: Stanislaw Gruszka <sgruszka@redhat.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: http://lkml.kernel.org/r/1359217182-25184-1-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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| .. | ||
| auto_group.c | ||
| auto_group.h | ||
| clock.c | ||
| core.c | ||
| cpupri.c | ||
| cpupri.h | ||
| cputime.c | ||
| debug.c | ||
| fair.c | ||
| features.h | ||
| idle_task.c | ||
| Makefile | ||
| rt.c | ||
| sched.h | ||
| stats.c | ||
| stats.h | ||
| stop_task.c | ||