Messages in this thread | | | Date | Tue, 17 May 2005 17:13:28 -0700 (PDT) | From | Christoph Lameter <> | Subject | Re: [PATCH] Optimize sys_times for a single thread process |
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On Tue, 17 May 2005, Andrew Morton wrote:
> Well, hrm, maybe. If this task has one sibling thread, and that thread is > in the process of exitting then (current == next_thread(current)) may > become true before that sibling thread has had a chance to dump its process > accounting info into the signal structure.
The task is only "unhashed" after the counters have been added in __exit_signal. See release_task in kernel/exit.c
> If that dumping happens prior to the __detach_pid() call then things are > probably OK (modulo memory ordering issues). Otherwise there's a little > window where the accounting will go wrong.
__exit_signal takes various locks that will insure the proper sequencing.
> Have you audited that code to ensure that the desired sequencing occurs in > all cases and that the appropriate barriers are in place?
AFAIK release task is always called for task removal.
> It all looks a bit fast-and-loose. If there are significant performance > benefits and these issues are loudly commented (they aren't at present) > then maybe-OK, I guess.
There are significant performance benefits in particular for one standard NUMA benchmark that keeps calling sys_times over and over. I believe other programs may exhibit the same brain dead behavior.
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