Messages in this thread | | | Subject | Re: [RFC PATCH 3/3 -v2] x86,smp: auto tune spinlock backoff delay factor | From | Eric Dumazet <> | Date | Thu, 03 Jan 2013 05:35:17 -0800 |
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On Thu, 2013-01-03 at 08:24 -0500, Steven Rostedt wrote: > On Thu, 2013-01-03 at 09:05 +0000, Jan Beulich wrote: > > > > How much bus traffic do monitor/mwait cause behind the scenes? > > > > I would suppose that this just snoops the bus for writes, but the > > amount of bus traffic involved in this isn't explicitly documented. > > > > One downside of course is that unless a spin lock is made occupy > > exactly a cache line, false wakeups are possible. > > And that would probably be very likely, as the whole purpose of Rik's > patches was to lower cache stalls due to other CPUs pounding on spin > locks that share the cache line of what is being protected (and > modified).
A monitor/mwait would be an option only if using MCS (or K42 variant) locks, where each cpu would wait on a private and dedicated cache line.
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