Re: [tip:perfcounters/urgent] perf_counter, x86: Fix/improve apic fallback

Johannes Stezenbach
2009-08-11T16:23:35Z

On Tue, Aug 11, 2009 at 11:34:21AM +0000, tip-bot for Ingo Molnar wrote:
> Commit-ID: 83f19150242ee57730a4331b6ae9a9b90ccc718c
> Gitweb: http://git.kernel.org/tip/83f19150242ee57730a4331b6ae9a9b90ccc718c
> Author: Ingo Molnar <mingo@elte.hu>
> AuthorDate: Tue, 11 Aug 2009 10:40:08 +0200
> Committer: Ingo Molnar <mingo@elte.hu>
> CommitDate: Tue, 11 Aug 2009 13:19:07 +0200
>
> perf_counter, x86: Fix/improve apic fallback
>
> Johannes Stezenbach reported that his Pentium-M based
> laptop does not have the local APIC enabled by default,
> and hence perfcounters do not get initialized.
>
> Add a fallback for this case: allow non-sampled counters
> and return with an error on sampled counters. This allows
> 'perf stat' to work out of box - and allows 'perf top'
> and 'perf record' to fall back on a hrtimer based sampling
> method.
>
> ( Passing 'lapic' on the boot line will allow hardware
> sampling to occur - but if the APIC is disabled
> permanently by the hardware then this fallback still
> allows more systems to use perfcounters. )
>
> Also decouple perfcounter support from X86_LOCAL_APIC.

Seems to work. From dmesg:

Performance Counters:
no APIC, boot with the "lapic" boot parameter to force-enable it.
no hardware sampling interrupt available.
p6 PMU driver.
... version: 0
... bit width: 32
... generic counters: 2
... value mask: 00000000ffffffff
... max period: 000000007fffffff
... fixed-purpose counters: 0
... counter mask: 0000000000000003
CPU: Intel(R) Pentium(R) M processor 1.80GHz stepping 06

However:

oprofile: using timer interrupt.

I tried "perf top", "perf stat -a sleep 1", "perf stat java foo",
it all looks good to my untrained eye.

Thanks,
Johannes