Messages in this thread | | | Date | Mon, 26 Sep 2005 11:11:34 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH linux-2.6 04/04] brsem: convert cpucontrol to brsem |
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Nathan Lynch wrote:
>Nick Piggin wrote: > >> >>Note that I happen to also think the idea (brsems) have merit, and >>that cpucontrol may be one of the places where a sane implementation >>would actually be useful... but at least when you're introducing >>this kind of complexity anywhere, you *really* need to be able to >>back it up with numbers. >> > >The only performance-related complaint with cpu hotplug of which I'm >aware -- that taking a cpu down on a large system can be painfully >slow -- resides in the "write side" of the code, which is not the case >that the brsem implementation optimizes. I think this patch would >make that case even worse. So I don't think it's appropriate to use a >brsem for cpu hotplug, especially without trying rwsem first. > >
I'm not sure that a brsem would make a noticable difference.
It isn't that cpu hotplug semaphore is a performance problem now, but that it isn't being used in as many cases as it could be due to its unscalable nature. For example, a while back I wanted to use it in the fork() path in the scheduler but couldn't.
Anyway, as I said, you need to be able to back it up with numbers ;)
Nick
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