Ingo Molnar wrote:
* Nick Piggin <[email protected]> wrote:
At the very least, the head waiter should not put itself on the end of
the FIFO when it finds the lock contended and waits again.
It's on my list. I had this implemented a couple of days ago, but then
profiled it and it turns out that the scenario isnt actually happening
in any significant way, not even on the most extreme 512-task workloads.
So i just removed the extra bloat. But i'll look at this again today,
together with some 'max delay' statistics.
That would be good.
If it isn't happening in a significant quantity, then something else
must be responsible for the performance increase. Arjan guesses the
double wakeups which could be the case, but I'd still put my money
on this issue (or maybe it is a combination of both).
Either way it would be good to work out where the performance is
coming from, and I do think fixing this is a good idea for fairness
(even though it may not technically improve deterministic max
latencies because there are still race windows)
--
SUSE Labs, Novell Inc.
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