Messages in this thread | | | Date | Wed, 14 Oct 2009 19:37:00 +0900 | From | Avi Kivity <> | Subject | Re: [PATCH RFC] sched: add notifier for process migration |
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On 10/14/2009 06:26 PM, Peter Zijlstra wrote: >> We already have one event notifier there - look at the >> perf_swcounter_event() callback. Why add a second one for essentially >> the same thing? >> >> We should only put a single callback there - a tracepoint defined via >> TRACE_EVENT() - and any secondary users can register a callback to the >> tracepoint itself. >> >> There's many similar places in the kernel - with notifier chains and >> also with a need to get tracepoints there. The fastest (and most >> consistent) solution is to add just a single event callback facility. >> > But that would basically mandate tracepoints to be always enabled, do we > want to go there? > > I don't think the overhead of tracepoints is understood well enough, > Jason you poked at that, do you have anything solid on that? > > Also, I can imagine the embedded people to not want that. > > I really like perf and tracepoints to not become co-dependent until > tracepoint become mandatory for all configurations. >
It would be cleanest to have both pvclock and tracepoints select migration notifiers, defaulting to off. Similarly both perf and kvm should use preemption notifiers (they do the same thing - switch per-task values into and out of cpu registers).
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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