On Fri, 2014-08-15 at 08:28 +0200, Peter Zijlstra wrote: > On Fri, Aug 15, 2014 at 07:19:31AM +0200, Mike Galbraith wrote: > > For the N threads doing this on N cores case, seems rq->lock hammering > > will still be a source of major box wide pain. Is there any correctness > > reason to add up unaccounted ->on_cpu beans, or is that just value > > added? > > That delta can be arbitrarily large with nohz_full. And without > nohz_full the error is nr_cpus*TICK_NSEC, which I bet is larger than the > reported clock resolution. > > Having a non-constant error bound is annoying for you never quite know > what to expect.
Ah, yeah, that could get rather large. > Also; why do we care about PROCESS_CPUTIME? People should really not use > it. What are the 'valid' usecases you guys care about? I don't care much, said "don't do that" before I saw a similar big box problem had popped up with times(). -Mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/