Messages in this thread | | | Date | Fri, 18 Feb 2011 14:45:19 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [RFC][PATCH 0/4] ftrace: Use -mfentry when supported (this is for x86_64 right now) |
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On 02/18/2011 02:39 PM, Andi Kleen wrote: > On Fri, Feb 18, 2011 at 03:10:18PM -0500, Dominique Toupin wrote: >> >> My understanding is stop_machine will stop all processors for many ms. > > I haven't measured it recently, but as long as the callback inside stop > machine is short it definitely shouldn't be "many ms". The latency > is bound by how long each CPU needs to answer to an interrupt, so if > you have some code that disables interrupts for a long time it will take > long -- but then your realtime response will be already bad. > > The interrupts are also done in parallel, so the interrupt latencies > don't add up. > > If all the CPUs answer in a reasonable time it's still not a cheap > operation, but nothing that takes "many ms". Most likely it's fine > for most soft real time purposes. >
We should also be able to use the breakpoint hack to avoid holding all the CPUs. They still need to be interrupted, but that skips the rendezvous operation.
-hpa
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