Messages in this thread | | | Date | Fri, 18 Feb 2011 23:39:02 +0100 | From | Andi Kleen <> | Subject | Re: [RFC][PATCH 0/4] ftrace: Use -mfentry when supported (this is for x86_64 right now) |
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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.
-Andi
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