Messages in this thread | | | Date | Thu, 25 Nov 2010 09:48:46 +0100 | Subject | Re: [RFC PATCH 2/3 v2] perf: Implement Nehalem uncore pmu | From | Stephane Eranian <> |
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On Thu, Nov 25, 2010 at 7:09 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > On Thu, 2010-11-25 at 08:24 +0800, Lin Ming wrote: >> On Tue, 2010-11-23 at 18:00 +0800, Stephane Eranian wrote: >> > On Sun, Nov 21, 2010 at 6:44 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: >> > > On Sun, 2010-11-21 at 22:04 +0800, Lin Ming wrote: >> > >> On Sun, 2010-11-21 at 20:46 +0800, Andi Kleen wrote: >> > >> > > >> > >> > > 2. Uncore pmu NMI handling >> > >> > > >> > >> > > All the 4 cores are programmed to receive uncore counter overflow >> > >> > > interrupt. The NMI handler(running on 1 of the 4 cores) handle all >> > >> > > counters enabled by all 4 cores. >> > >> > >> > >> > Really for uncore monitoring there is no need to use an NMI handler. >> > >> > You can't profile a core anyways, so you can just delay the reporting >> > >> > a little bit. It may simplify the code to not use one here >> > >> > and just use an ordinary handler. >> > >> >> > >> OK, I can use on ordinary interrupt handler here. >> > > >> > > Does the hardware actually allow using a different interrupt source? >> > > >> > It does not. It's using whatever you've programmed into the APIC >> > LVT vector, AFAIK. Uncore interrupt mode is enabled via >> > IA32_DEBUGCTL. Regarless of sampling or not, you need the interrupt >> > to virtualize the counters to 64 bits. >> >> If only counting(perf stat) makes sense for uncore events, do we still >> need an interrupt handler? > > Yep, I see no reason to dis-allow sampling. Sure its hard to make sense > of it, but since there are people who offline all but one cpu of a > package, I bet there are people who will run just one task on a package > as well. > > Just because it doesn't make sense in general doesn't mean there isn't > anybody who'd want to do it and actually knows wth he's doing. > >> 48 bits counter is not that easy to overflow in practice. > > Still.. > Agreed.
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