On Thu, May 16, 2013 at 11:09:16AM +0200, Peter Zijlstra wrote:
> How about something like the below? It also adds the branch flags Mikey wanted
> for PowerPC.
The asymmetry is unfortunate, but I think its more useful to have the from
kernel branch target than it is not to have it. This way you at least know
there was a kernel entry/exit and where you've continued.
Without either branch to kernel and branch from kernel entries you'd be
wondering WTF happend to your control flow.
> ---
> arch/x86/kernel/cpu/perf_event_intel_lbr.c | 12 +++++++++---
> include/linux/perf_event.h | 10 +++++++---
> 2 files changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> index d978353..f44d635 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> @@ -585,17 +585,23 @@ intel_pmu_lbr_filter(struct cpu_hw_events *cpuc)
>
> /* if type does not correspond, then discard */
> if (type == X86_BR_NONE || (br_sel & type) != type) {
> - cpuc->lbr_entries[i].from = 0;
> + cpuc->lbr_entries[i].__delete = 1;
> compress = true;
> }
> +
> + /* hide kernel addresses if we're not privileged */
> + if (!(br_sel & X86_BR_KERNEL) && kernel_ip(from)) {
> + cpuc->lbr_entries[i].from = -1L;
> + cpuc->lbr_entries[i].invalid_from = 1;
> + }
> }
>
> if (!compress)
> return;
>
> - /* remove all entries with from=0 */
> + /* remove all entries with __delete */
> for (i = 0; i < cpuc->lbr_stack.nr; ) {
> - if (!cpuc->lbr_entries[i].from) {
> + if (cpuc->lbr_entries[i].__delete) {
> j = i;
> while (++j < cpuc->lbr_stack.nr)
> cpuc->lbr_entries[j-1] = cpuc->lbr_entries[j];
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index f463a46..7acf1c9 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -77,9 +77,13 @@ struct perf_raw_record {
> struct perf_branch_entry {
> __u64 from;
> __u64 to;
> - __u64 mispred:1, /* target mispredicted */
> - predicted:1,/* target predicted */
> - reserved:62;
> + __u64 mispred:1, /* target mispredicted */
> + predicted:1, /* target predicted */
> + invalid_to:1, /* @to isn't to be trusted */
> + invalid_from:1, /* @from isn't to be trusted */
> + reserved:59,
> + __delete:1; /* Implementation; userspace should
> + always see a 0 */
> };
>
> /*
>
--
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