Messages in this thread | | | Date | Wed, 18 Sep 2002 19:24:40 +0200 (CEST) | From | Ingo Molnar <> | Subject | Re: [patch] lockless, scalable get_pid(), for_each_process() elimination, 2.5.35-BK |
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On Wed, 18 Sep 2002, Linus Torvalds wrote:
> And guys, if this is a performance problem for some extreme site, the > fix is truly trivial: > > echo $((0x7fffffff)) > /proc/sys/max_pid > > and you're done.
it is a problem still. We can create/destroy 2 billion threads:
venus:~> ./p3 -s 2000000 -t 10 -r 0 -T --sync-join Runtime: 19.889182138 seconds
in roughly 5 hours, on bog-standard 2-CPU x86 hardware. Or in 1.25 hours on an 8-way box. And then we are back to step #1: trying to pass over already allocated PIDs by destroying the contents of the L1 and L2 cache once for each allocated PID passed. Sure, with 2 billion PIDs space that averages out, but it's an algorithm with a very nasty worst-case behavior, which is not so hard to trigger.
Plus the not-so-unlikely case of having to pass a couple of tens of thousands of allocated PIDs, in a couple of minutes, with all user input blocked, and interrupts disabled, website silent. Obviously sites will not create threads at such a high rate as demonstrated above, so it will 'only' happen once every couple of days, or every couple of weeks.
Ingo
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