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SubjectRe: [PATCH -tip v3 2/5] perf: change perf_event_header.misc to PERF_RECORD_MISC_USER for BTS
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On Thu, 2011-08-11 at 21:06 +0900, Akihiro Nagai wrote:
> Change perf_event_headder.misc to PERF_RECORD_MISC_USER for
> BTS records, because BTS traces both kernel and user spaces
> nevertheless perf specifies to trace only kernel or user space.

Now I'm confused..

If BTS traces both kernel and user, the MISC bit should reflect the
right state per-sample, on x86 that's easy enough to do by the address.


> ---
>
> arch/x86/kernel/cpu/perf_event_intel_ds.c | 8 ++++++++
> 1 files changed, 8 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c b/arch/x86/kernel/cpu/perf_event_intel_ds.c
> index 1b1ef3a..323f3f0 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_ds.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c
> @@ -340,6 +340,14 @@ static int intel_pmu_drain_bts_buffer(void)
> */
> perf_prepare_sample(&header, &data, event, &regs);
>
> + /*
> + * Since BTS can not trace kernel and user space separately, set

Uhm, IA32_DEBUGCTL_MSR.BTS_OFF_{OS,USR} seem to suggest it can?!
> + * PERF_RECORD_MISC_USER in header.misc to resolve both kernel and
> + * user DSOs and symbols.
> + */
> + header.misc &= ~PERF_RECORD_MISC_CPUMODE_MASK;
> + header.misc |= PERF_RECORD_MISC_USER;


So what's wrong with something like:

header.misc |= is_kernel_address(at->from) ?
PERF_RECORD_MISC_KERNEL :
PERF_RECORD_MISC_USER;
> if (perf_output_begin(&handle, event, header.size * (top - at)))
> return 1;
>
>



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