Messages in this thread | | | Date | Mon, 4 Jun 2012 15:12:49 +0200 | Subject | Re: [PATCH] perf: Fix intel shared extra msr allocation | From | Stephane Eranian <> |
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On Fri, Jun 1, 2012 at 4:11 PM, Yan, Zheng <zheng.z.yan@linux.intel.com> wrote: > On Fri, Jun 1, 2012 at 5:35 PM, Stephane Eranian <eranian@google.com> wrote: >> On Fri, Jun 1, 2012 at 5:20 AM, Yan, Zheng <zheng.z.yan@intel.com> wrote: >>> From: "Yan, Zheng" <zheng.z.yan@intel.com> >>> >>> intel_shared_reg_get/put_constraints() can be indirectly called >>> by validate_group(). In that case, they should avoid modifying >>> the perf_event date structure because the event can be already >>> in active state. Otherwise the shared extra msr's reference >>> count will be left in inconsistent state. >>> >> I understand the problem but I am wondering if you actually saw >> it in real life. The reason I am asking is because of the way >> validate_group() collects the events and how they are added >> to sibling_list. The new event is added at the tail. Thus it will >> come last, and will get to __intel_shared_reg_get_constraints() >> last, thus I am wondering if it can really modify the programming >> on the existing events. > > The real problem is from __intel_shared_reg_put_constraints(). it set > reg->alloc to 0 and decreases fake_cpuc->shared_regs->regs[reg->idx]'s > reference count. Later when deleting the event, put_constraints() will find > reg->alloc is 0 and it won't decrease the shared msr's reference count. > > Run 'perf stat --group -a -C 0 -e LLC-loads -e LLC-stores sleep 1" on > Nehalem can trigger the bug. > And what do you see in this particular example?
I'd like to see the results via libpfm4 and /perf_examples/syst_count: $ sudo ./syst_count -e offcore_response_0:dmnd_data_rd -eoffcore_response_0:dmnd_rfo -p -d 10 -c 0
Should see 50% for each event group.
>> >> See more comments inline. >> >>> Signed-off-by: Zheng Yan <zheng.z.yan@intel.com> >>> --- >>> arch/x86/kernel/cpu/perf_event_intel.c | 31 +++++++++++++++++++++++-------- >>> 1 files changed, 23 insertions(+), 8 deletions(-) >>> >>> diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c >>> index 166546e..10840d0 100644 >>> --- a/arch/x86/kernel/cpu/perf_event_intel.c >>> +++ b/arch/x86/kernel/cpu/perf_event_intel.c >>> @@ -1119,11 +1119,21 @@ intel_bts_constraints(struct perf_event *event) >>> return NULL; >>> } >>> >>> -static bool intel_try_alt_er(struct perf_event *event, int orig_idx) >>> +static bool intel_try_alt_er(struct perf_event *event, int *idx, >>> + int orig_idx, bool fake_cpuc) >>> { >>> - if (!(x86_pmu.er_flags & ERF_HAS_RSP_1)) >>> + if (!(x86_pmu.er_flags & ERF_HAS_RSP_1) || *idx != orig_idx) >>> return false; >>> >>> + /* don't modify the event structure if the cpuc is faked */ >>> + if (fake_cpuc) { >>> + if (*idx == EXTRA_REG_RSP_0) >>> + *idx = EXTRA_REG_RSP_1; >>> + else if (*idx == EXTRA_REG_RSP_1) >>> + *idx = EXTRA_REG_RSP_0; >>> + return (*idx != orig_idx); >>> + } >>> + >> I understand that. >> >>> if (event->hw.extra_reg.idx == EXTRA_REG_RSP_0) { >>> event->hw.config &= ~INTEL_ARCH_EVENT_MASK; >>> event->hw.config |= 0x01bb; >>> @@ -1139,6 +1149,7 @@ static bool intel_try_alt_er(struct perf_event *event, int orig_idx) >>> if (event->hw.extra_reg.idx == orig_idx) >>> return false; >>> >>> + *idx = event->hw.extra_reg.idx; >>> return true; >>> } >>> >>> @@ -1155,16 +1166,18 @@ __intel_shared_reg_get_constraints(struct cpu_hw_events *cpuc, >>> struct hw_perf_event_extra *reg) >>> { >>> struct event_constraint *c = &emptyconstraint; >>> + struct intel_shared_regs *shared_regs = cpuc->shared_regs; >>> struct er_account *era; >>> unsigned long flags; >>> int orig_idx = reg->idx; >>> + int idx = orig_idx; >>> >>> - /* already allocated shared msr */ >>> - if (reg->alloc) >>> + /* shared msr is already allocated and cpuc is not faked */ >>> + if (reg->alloc && shared_regs->core_id != -1) >>> return NULL; /* call x86_get_event_constraint() */ >>> >> I don't understand what you need this stuff. Shared_regs is faked as well. > > The event can be in active state, we should avoid clearing reg->alloc. > > Regards > Yan, Zheng -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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