[PATCH 3/3] alpha: Implement HW performance events on the EV67 and later CPUs.
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From: Michael Cree on 27 Jul 2010 06:40 On 04/05/10 19:40, Peter Zijlstra wrote: > On Sat, 2010-05-01 at 11:55 +1200, Michael Cree wrote: >> +/* I wonder what this is for ??? */ >> +void set_perf_event_pending(void) >> +{ >> +} > > If the PMU Interrupt comes in as an NMI we cannot take locks and such > from its handler. So what we do is queue that work to be ran later. The > kernel has a fallback to run this stuff from the timer hardirq, but if > the PMI is IRQ context (like ARM) you can simply call > perf_event_do_pending() at its tail. > > Alternatively you can self-IPI like x86 does and run > perf_event_do_pending() from there. OK, I couldn't see how to self-IPI on the Apha (there is no obvious way in the Alpha arch code, and the Alpha HW Ref. Man. only describes such a feature being supported by the PALcode for OpenVMS which we are obviously not running) and the PMI on Alpha is at such a high priority there is no chance that the lock can be freed while in the PMI handler, so I have put the call to perf_event_do_pending() in the timer interrupt, but unlike the PowerPC code I don't know any tricks to force the timer interrupt to happen early when there is pending work, so there is a potential maximum delay of 1ms from pending work being notified to calling perf_event_do_pending(). Is this delay acceptable? I also fix a nasty, but heretofore hidden, bug that could completely lock up a machine with continuous PMIs due to a throttled PMC being accidently re-enabled by the other PMC. It only showed up when I set the NMI flag true in the call to perf_event_overflow() and had two events counting simultaneously with a very short sample period. I also see the x86 and Sparc code in 2.6.35 have reimplemented the call to hw_perf_group_sched_in() in terms of new functions start_txn(), cancel_txn() and commit_txn(). Is this change necessary to get the Alpha code accepted for 2.6.36? If so it would be helpful if I could have a brief description of what each function does. The updated patch follows this message. Cheers Michael. Michael Cree (1): alpha: Implement HW performance events on the EV67 and later CPUs. arch/alpha/include/asm/perf_event.h | 8 +- arch/alpha/kernel/Makefile | 1 + arch/alpha/kernel/irq_alpha.c | 3 + arch/alpha/kernel/perf_event.c | 842 +++++++++++++++++++++++++++++++++++ arch/alpha/kernel/time.c | 26 ++ 5 files changed, 879 insertions(+), 1 deletions(-) create mode 100644 arch/alpha/kernel/perf_event.c -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |