Messages in this thread | | | Date | Fri, 27 Jan 2012 10:56:09 +0530 | From | Anshuman Khandual <> | Subject | Re: [PATCH 04/13] perf_events: sync branch stack sampling with X86 precise_sampling (v3) |
| |
On Monday 09 January 2012 10:19 PM, Stephane Eranian wrote: > If precise sampling is enabled on Intel X86, then perf_event uses PEBS. > To correct for the off-by-one error of PEBS, perf_event uses LBR when > precise_sample > 1. > > On Intel X86 PERF_SAMPLE_BRANCH_STACK is implemented using LBR, > therefore both features must be coordinated as they may not > configure LBR the same way. > > For PEBS, LBR needs to capture all branches at all priv levels. > This patch sets this up. > > The configuration of PERF_SAMPLE_BRANCH_STACK may not be compatible > in which case an error must be returned. > > Signed-off-by: Stephane Eranian <eranian@google.com> Reviewed by: Anshuman Khandual<khandual@linux.vnet.ibm.com> > --- > arch/x86/kernel/cpu/perf_event.c | 22 ++++++++++++++++++++++ > 1 files changed, 22 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c > index 3779313..710ec93 100644 > --- a/arch/x86/kernel/cpu/perf_event.c > +++ b/arch/x86/kernel/cpu/perf_event.c > @@ -356,6 +356,7 @@ int x86_setup_perfctr(struct perf_event *event) > int x86_pmu_hw_config(struct perf_event *event) > { > if (event->attr.precise_ip) { > + u64 *br_type, br_sel; > int precise = 0; > > /* Support for constant skid */ > @@ -369,6 +370,27 @@ int x86_pmu_hw_config(struct perf_event *event) > > if (event->attr.precise_ip > precise) > return -EOPNOTSUPP; > + /* > + * check that PEBS LBR correction does not conflict with > + * whatever the user is asking with attr->branch_sample_type > + */ > + if (event->attr.precise_ip > 1) { > + > + br_type = &event->attr.branch_sample_type; > + > + if (has_branch_stack(event)) { > + br_sel = *br_type & PERF_SAMPLE_BRANCH_ANY; > + if (br_sel != PERF_SAMPLE_BRANCH_ANY) > + return -EOPNOTSUPP; > + } else { > + /* > + * For PEBS fixups, we capture all > + * the branches at all priv levels > + */ > + *br_type = PERF_SAMPLE_BRANCH_ANY > + | PERF_SAMPLE_BRANCH_PLM_ALL; > + } > + } > } > > /*
-- Linux Technology Centre IBM Systems and Technology Group Bangalore India
| |