Date: Mon, 18 Feb 2002 13:34:33 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Julian Elischer <julian@elischer.org> Cc: current@FreeBSD.ORG Subject: Re: Patch to improve mutex collision performance Message-ID: <200202182134.g1ILYXi42633@apollo.backplane.com> References: <Pine.BSF.4.21.0202181310500.52663-100000@InterJet.elischer.org>
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:>
:> :can you detail in more clarity the flip-flopping you were seeing?
:>
:> Basically what is happening is that switch/wakeup overhead is being
:> imposed unnecessarily. There is no need to switch if there is nothing
:> to switch to, and this also causes the other process to not have to
:> wakeup anyone when it releases Giant because process #1 is spinning
:> on it instead of sleeping on it. So you immediate remove four context
:> switches from the critical path.
:
:true, though the original code would halt the processor to reduce power
:consumption on laptops etc. procrunnable doesn't include the idle
:process. (a side-effect).
That would still work, the spin only occurs when multiple cpus are vying
for a sleep lock. But it's moot now, something isn't working as expected.
It's as though procrunnable() is broken.
-Matt
Matthew Dillon
<dillon@backplane.com>
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