• Rik van Riel's avatar
    time, signal: Protect resource use statistics with seqlock · e78c3496
    Rik van Riel authored
    Both times() and clock_gettime(CLOCK_PROCESS_CPUTIME_ID) have scalability
    issues on large systems, due to both functions being serialized with a
    lock.
    
    The lock protects against reporting a wrong value, due to a thread in the
    task group exiting, its statistics reporting up to the signal struct, and
    that exited task's statistics being counted twice (or not at all).
    
    Protecting that with a lock results in times() and clock_gettime() being
    completely serialized on large systems.
    
    This can be fixed by using a seqlock around the events that gather and
    propagate statistics. As an additional benefit, the protection code can
    be moved into thread_group_cputime(), slightly simplifying the calling
    functions.
    
    In the case of posix_cpu_clock_get_task() things can be simplified a
    lot, because the calling function already ensures that the task sticks
    around, and the rest is now taken care of in thread_group_cputime().
    
    This way the statistics reporting code can run lockless.
    Signed-off-by: default avatarRik van Riel <riel@redhat.com>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Alex Thorlton <athorlton@sgi.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Daeseok Youn <daeseok.youn@gmail.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
    Cc: Geert Uytterhoeven <geert@linux-m68k.org>
    Cc: Guillaume Morin <guillaume@morinfr.org>
    Cc: Ionut Alexa <ionut.m.alexa@gmail.com>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Li Zefan <lizefan@huawei.com>
    Cc: Michal Hocko <mhocko@suse.cz>
    Cc: Michal Schmidt <mschmidt@redhat.com>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Vladimir Davydov <vdavydov@parallels.com>
    Cc: umgwanakikbuti@gmail.com
    Cc: fweisbec@gmail.com
    Cc: srao@redhat.com
    Cc: lwoodman@redhat.com
    Cc: atheurer@redhat.com
    Link: http://lkml.kernel.org/r/20140816134010.26a9b572@annuminas.surriel.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    e78c3496
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