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Date: Thu, 27 Jun 2013 09:52:22 +0800
From: "Yan, Zheng" <zheng.z.yan@...el.com>
To: Stephane Eranian <eranian@...gle.com>
CC: LKML <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 6/7] perf, x86: Use LBR call stack to get user callchain
On 06/26/2013 08:45 PM, Stephane Eranian wrote:
> Hi,
>
> And I think the reason why kernel is not possible deserves
> a full explanation in the changelog and in the code.
> It is still not clear to me whether this is a hw bug or a
> limitation.
It's a hardware bug. The problem I encountered is: if FREEZE_ON_PMI bit is set and
PMI happens near call/return instruction, the LBR_TOS register may have a superfluous
increase/decrease. (increase/decrease by two for call/return instruction)
Regards
Yan, Zheng
>
>
> On Wed, Jun 26, 2013 at 2:42 PM, Stephane Eranian <eranian@...gle.com> wrote:
>> On Tue, Jun 25, 2013 at 10:47 AM, Yan, Zheng <zheng.z.yan@...el.com> wrote:
>>> From: "Yan, Zheng" <zheng.z.yan@...el.com>
>>>
>>> Try enabling the LBR call stack feature if event request recording
>>> callchain. Try utilizing the LBR call stack to get user callchain
>>> in case of there is no frame pointer.
>>>
>>> This patch also adds a cpu pmu attribute to enable/disable this
>>> feature.
>>>
>>> Signed-off-by: Yan, Zheng <zheng.z.yan@...el.com>
>>> ---
>>> arch/x86/kernel/cpu/perf_event.c | 128 +++++++++++++++++++++--------
>>> arch/x86/kernel/cpu/perf_event.h | 7 ++
>>> arch/x86/kernel/cpu/perf_event_intel.c | 20 ++---
>>> arch/x86/kernel/cpu/perf_event_intel_lbr.c | 3 +
>>> include/linux/perf_event.h | 6 ++
>>> kernel/events/core.c | 11 ++-
>>> 6 files changed, 126 insertions(+), 49 deletions(-)
>>>
>>> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
>>> index 639aa4d..a07eb03 100644
>>> --- a/arch/x86/kernel/cpu/perf_event.c
>>> +++ b/arch/x86/kernel/cpu/perf_event.c
>>> @@ -399,37 +399,49 @@ 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 && x86_pmu.intel_cap.pebs_format < 2) {
>>> + u64 *br_type = &event->attr.branch_sample_type;
>>> +
>>> + if (has_branch_stack(event)) {
>>> + if (!precise_br_compat(event))
>>> + return -EOPNOTSUPP;
>>> +
>>> + /* branch_sample_type is compatible */
>>> +
>>> + } else {
>>> + /*
>>> + * user did not specify branch_sample_type
>>> + *
>>> + * For PEBS fixups, we capture all
>>> + * the branches at the priv level of the
>>> + * event.
>>> + */
>>> + *br_type = PERF_SAMPLE_BRANCH_ANY;
>>> +
>>> + if (!event->attr.exclude_user)
>>> + *br_type |= PERF_SAMPLE_BRANCH_USER;
>>> +
>>> + if (!event->attr.exclude_kernel)
>>> + *br_type |= PERF_SAMPLE_BRANCH_KERNEL;
>>> + }
>>> + } else if ((event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) &&
>>> + !has_branch_stack(event) &&
>>> + x86_pmu.attr_lbr_callstack &&
>>> + !event->attr.exclude_user &&
>>> + (event->attach_state & PERF_ATTACH_TASK)) {
>>
>> Yes, that's the test but it is wrong. I can pass the test if
>> I have exclude_user = exclude_kernel = 0.
>>
>> You want:
>> !event->attr.exclude_user && event->attr.exclude_kernel &&
>>
>> I tested that and it works.
>>
>>> /*
>>> - * check that PEBS LBR correction does not conflict with
>>> - * whatever the user is asking with attr->branch_sample_type
>>> + * user did not specify branch_sample_type,
>>> + * try using the LBR call stack facility to
>>> + * record call chains of user program.
>>> */
>>> - if (event->attr.precise_ip > 1 &&
>>> - x86_pmu.intel_cap.pebs_format < 2) {
>>> - u64 *br_type = &event->attr.branch_sample_type;
>>> -
>>> - if (has_branch_stack(event)) {
>>> - if (!precise_br_compat(event))
>>> - return -EOPNOTSUPP;
>>> -
>>> - /* branch_sample_type is compatible */
>>> -
>>> - } else {
>>> - /*
>>> - * user did not specify branch_sample_type
>>> - *
>>> - * For PEBS fixups, we capture all
>>> - * the branches at the priv level of the
>>> - * event.
>>> - */
>>> - *br_type = PERF_SAMPLE_BRANCH_ANY;
>>> -
>>> - if (!event->attr.exclude_user)
>>> - *br_type |= PERF_SAMPLE_BRANCH_USER;
>>> -
>>> - if (!event->attr.exclude_kernel)
>>> - *br_type |= PERF_SAMPLE_BRANCH_KERNEL;
>>> - }
>>> - }
>>> + event->attr.branch_sample_type =
>>> + PERF_SAMPLE_BRANCH_USER |
>>> + PERF_SAMPLE_BRANCH_CALL_STACK;
>>> }
>>>
>>> /*
>>> @@ -1825,10 +1837,34 @@ static ssize_t set_attr_rdpmc(struct device *cdev,
>>> return count;
>>> }
>>>
>>> +static ssize_t get_attr_lbr_callstack(struct device *cdev,
>>> + struct device_attribute *attr, char *buf)
>>> +{
>>> + return snprintf(buf, 40, "%d\n", x86_pmu.attr_lbr_callstack);
>>> +}
>>> +
>>> +static ssize_t set_attr_lbr_callstack(struct device *cdev,
>>> + struct device_attribute *attr,
>>> + const char *buf, size_t count)
>>> +{
>>> + unsigned long val = simple_strtoul(buf, NULL, 0);
>>> +
>>> + if (x86_pmu.attr_lbr_callstack != !!val) {
>>> + if (val && !x86_pmu_has_lbr_callstack())
>>> + return -EOPNOTSUPP;
>>> + x86_pmu.attr_lbr_callstack = !!val;
>>> + }
>>> + return count;
>>> +}
>>> +
>>> static DEVICE_ATTR(rdpmc, S_IRUSR | S_IWUSR, get_attr_rdpmc, set_attr_rdpmc);
>>> +static DEVICE_ATTR(lbr_callstack, S_IRUSR | S_IWUSR,
>>> + get_attr_lbr_callstack, set_attr_lbr_callstack);
>>> +
>>>
>>> static struct attribute *x86_pmu_attrs[] = {
>>> &dev_attr_rdpmc.attr,
>>> + &dev_attr_lbr_callstack.attr,
>>> NULL,
>>> };
>>>
>>> @@ -1955,12 +1991,29 @@ static unsigned long get_segment_base(unsigned int segment)
>>> return get_desc_base(desc + idx);
>>> }
>>>
>>> +static inline void
>>> +perf_callchain_lbr_callstack(struct perf_callchain_entry *entry,
>>> + struct perf_sample_data *data)
>>> +{
>>> + struct perf_branch_stack *br_stack = data->br_stack;
>>> +
>>> + if (br_stack && br_stack->user_callstack &&
>>> + x86_pmu.attr_lbr_callstack) {
>>> + int i = 0;
>>> + while (i < br_stack->nr && entry->nr < PERF_MAX_STACK_DEPTH) {
>>> + perf_callchain_store(entry, br_stack->entries[i].from);
>>> + i++;
>>> + }
>>> + }
>>> +}
>>> +
>>> #ifdef CONFIG_COMPAT
>>>
>>> #include <asm/compat.h>
>>>
>>> static inline int
>>> -perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry *entry)
>>> +perf_callchain_user32(struct perf_callchain_entry *entry,
>>> + struct pt_regs *regs, struct perf_sample_data *data)
>>> {
>>> /* 32-bit process in 64-bit kernel. */
>>> unsigned long ss_base, cs_base;
>>> @@ -1989,11 +2042,16 @@ perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry *entry)
>>> perf_callchain_store(entry, cs_base + frame.return_address);
>>> fp = compat_ptr(ss_base + frame.next_frame);
>>> }
>>> +
>>> + if (fp == compat_ptr(regs->bp))
>>> + perf_callchain_lbr_callstack(entry, data);
>>> +
>>> return 1;
>>> }
>>> #else
>>> static inline int
>>> -perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry *entry)
>>> +perf_callchain_user32(struct perf_callchain_entry *entry,
>>> + struct pt_regs *regs, struct perf_sample_data *data)
>>> {
>>> return 0;
>>> }
>>> @@ -2023,12 +2081,12 @@ void perf_callchain_user(struct perf_callchain_entry *entry,
>>> if (!current->mm)
>>> return;
>>>
>>> - if (perf_callchain_user32(regs, entry))
>>> + if (perf_callchain_user32(entry, regs, data))
>>> return;
>>>
>>> while (entry->nr < PERF_MAX_STACK_DEPTH) {
>>> unsigned long bytes;
>>> - frame.next_frame = NULL;
>>> + frame.next_frame = NULL;
>>> frame.return_address = 0;
>>>
>>> bytes = copy_from_user_nmi(&frame, fp, sizeof(frame));
>>> @@ -2041,6 +2099,10 @@ void perf_callchain_user(struct perf_callchain_entry *entry,
>>> perf_callchain_store(entry, frame.return_address);
>>> fp = frame.next_frame;
>>> }
>>> +
>>> + /* try LBR callstack if there is no frame pointer */
>>> + if (fp == (void __user *)regs->bp)
>>> + perf_callchain_lbr_callstack(entry, data);
>>> }
>>>
>>> /*
>>> diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
>>> index 0116970..536470d 100644
>>> --- a/arch/x86/kernel/cpu/perf_event.h
>>> +++ b/arch/x86/kernel/cpu/perf_event.h
>>> @@ -390,6 +390,7 @@ struct x86_pmu {
>>> * sysfs attrs
>>> */
>>> int attr_rdpmc;
>>> + int attr_lbr_callstack;
>>> struct attribute **format_attrs;
>>> struct attribute **event_attrs;
>>>
>>> @@ -496,6 +497,12 @@ static struct perf_pmu_events_attr event_attr_##v = { \
>>>
>>> extern struct x86_pmu x86_pmu __read_mostly;
>>>
>>> +static inline bool x86_pmu_has_lbr_callstack(void)
>>> +{
>>> + return x86_pmu.lbr_sel_map &&
>>> + x86_pmu.lbr_sel_map[PERF_SAMPLE_BRANCH_CALL_STACK_SHIFT] > 0;
>>> +}
>>> +
>>> DECLARE_PER_CPU(struct cpu_hw_events, cpu_hw_events);
>>>
>>> int x86_perf_event_set_period(struct perf_event *event);
>>> diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
>>> index f59b46e..baa8384 100644
>>> --- a/arch/x86/kernel/cpu/perf_event_intel.c
>>> +++ b/arch/x86/kernel/cpu/perf_event_intel.c
>>> @@ -882,15 +882,10 @@ static __initconst const u64 atom_hw_cache_event_ids
>>> },
>>> };
>>>
>>> -static inline bool intel_pmu_needs_lbr_smpl(struct perf_event *event)
>>> +static inline bool intel_pmu_needs_lbr_callstack(struct perf_event *event)
>>> {
>>> - /* user explicitly requested branch sampling */
>>> - if (has_branch_stack(event))
>>> - return true;
>>> -
>>> - /* implicit branch sampling to correct PEBS skid */
>>> - if (x86_pmu.intel_cap.pebs_trap && event->attr.precise_ip > 1 &&
>>> - x86_pmu.intel_cap.pebs_format < 2)
>>> + if ((event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) &&
>>> + (event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_CALL_STACK))
>>> return true;
>>>
>>> return false;
>>> @@ -1054,7 +1049,7 @@ static void intel_pmu_disable_event(struct perf_event *event)
>>> * must disable before any actual event
>>> * because any event may be combined with LBR
>>> */
>>> - if (intel_pmu_needs_lbr_smpl(event))
>>> + if (needs_branch_stack(event))
>>> intel_pmu_lbr_disable(event);
>>>
>>> if (unlikely(hwc->config_base == MSR_ARCH_PERFMON_FIXED_CTR_CTRL)) {
>>> @@ -1115,7 +1110,7 @@ static void intel_pmu_enable_event(struct perf_event *event)
>>> * must enabled before any actual event
>>> * because any event may be combined with LBR
>>> */
>>> - if (intel_pmu_needs_lbr_smpl(event))
>>> + if (needs_branch_stack(event))
>>> intel_pmu_lbr_enable(event);
>>>
>>> if (event->attr.exclude_host)
>>> @@ -1237,7 +1232,8 @@ again:
>>>
>>> perf_sample_data_init(&data, 0, event->hw.last_period);
>>>
>>> - if (has_branch_stack(event))
>>> + if (has_branch_stack(event) ||
>>> + (event->ctx->task && intel_pmu_needs_lbr_callstack(event)))
>>> data.br_stack = &cpuc->lbr_stack;
>>>
>>> if (perf_event_overflow(event, &data, regs))
>>> @@ -1568,7 +1564,7 @@ static int intel_pmu_hw_config(struct perf_event *event)
>>> if (event->attr.precise_ip && x86_pmu.pebs_aliases)
>>> x86_pmu.pebs_aliases(event);
>>>
>>> - if (intel_pmu_needs_lbr_smpl(event)) {
>>> + if (needs_branch_stack(event)) {
>>> ret = intel_pmu_setup_lbr_filter(event);
>>> if (ret)
>>> return ret;
>>> diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
>>> index 43b16b4..3be2d7b 100644
>>> --- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
>>> +++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
>>> @@ -709,6 +709,8 @@ intel_pmu_lbr_filter(struct cpu_hw_events *cpuc)
>>> int i, j, type;
>>> bool compress = false;
>>>
>>> + cpuc->lbr_stack.user_callstack = branch_user_callstack(br_sel);
>>> +
>>> /* if sampling all branches, then nothing to filter */
>>> if ((br_sel & X86_BR_ALL) == X86_BR_ALL)
>>> return;
>>> @@ -861,6 +863,7 @@ void intel_pmu_lbr_init_hsw(void)
>>>
>>> x86_pmu.lbr_sel_mask = LBR_SEL_MASK;
>>> x86_pmu.lbr_sel_map = hsw_lbr_sel_map;
>>> + x86_pmu.attr_lbr_callstack = 1;
>>>
>>> pr_cont("16-deep LBR, ");
>>> }
>>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>>> index fa4c1bf..168e66e 100644
>>> --- a/include/linux/perf_event.h
>>> +++ b/include/linux/perf_event.h
>>> @@ -97,6 +97,7 @@ struct perf_branch_entry {
>>> * recent branch.
>>> */
>>> struct perf_branch_stack {
>>> + unsigned user_callstack:1;
>>> __u64 nr;
>>> struct perf_branch_entry entries[0];
>>> };
>>> @@ -759,6 +760,11 @@ static inline bool has_branch_stack(struct perf_event *event)
>>> return event->attr.sample_type & PERF_SAMPLE_BRANCH_STACK;
>>> }
>>>
>>> +static inline bool needs_branch_stack(struct perf_event *event)
>>> +{
>>> + return event->attr.branch_sample_type != 0;
>>> +}
>>> +
>>> extern int perf_output_begin(struct perf_output_handle *handle,
>>> struct perf_event *event, unsigned int size);
>>> extern void perf_output_end(struct perf_output_handle *handle);
>>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>>> index 4aad901..38eaa2b 100644
>>> --- a/kernel/events/core.c
>>> +++ b/kernel/events/core.c
>>> @@ -1117,7 +1117,7 @@ list_add_event(struct perf_event *event, struct perf_event_context *ctx)
>>> if (is_cgroup_event(event))
>>> ctx->nr_cgroups++;
>>>
>>> - if (has_branch_stack(event))
>>> + if (needs_branch_stack(event))
>>> ctx->nr_branch_stack++;
>>>
>>> list_add_rcu(&event->event_entry, &ctx->event_list);
>>> @@ -1274,7 +1274,7 @@ list_del_event(struct perf_event *event, struct perf_event_context *ctx)
>>> cpuctx->cgrp = NULL;
>>> }
>>>
>>> - if (has_branch_stack(event)) {
>>> + if (needs_branch_stack(event)) {
>>> if (ctx->is_active)
>>> __get_cpu_var(perf_branch_stack_events)--;
>>> ctx->nr_branch_stack--;
>>> @@ -3155,7 +3155,7 @@ static void free_event(struct perf_event *event)
>>> static_key_slow_dec_deferred(&perf_sched_events);
>>> }
>>>
>>> - if (has_branch_stack(event))
>>> + if (needs_branch_stack(event))
>>> static_key_slow_dec_deferred(&perf_sched_events);
>>> }
>>>
>>> @@ -6545,6 +6545,9 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
>>> if (attr->inherit && (attr->read_format & PERF_FORMAT_GROUP))
>>> goto done;
>>>
>>> + if (!has_branch_stack(event))
>>> + event->attr.branch_sample_type = 0;
>>> +
>>> pmu = perf_init_event(event);
>>>
>>> done:
>>> @@ -6577,7 +6580,7 @@ done:
>>> return ERR_PTR(err);
>>> }
>>> }
>>> - if (has_branch_stack(event))
>>> + if (needs_branch_stack(event))
>>> static_key_slow_inc(&perf_sched_events.key);
>>> }
>>>
>>> --
>>> 1.8.1.4
>>>
--
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