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Date: Fri, 28 Jun 2013 10:24:45 +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 06/27/2013 04:58 PM, Stephane Eranian wrote:
> On Thu, Jun 27, 2013 at 3:40 AM, Yan, Zheng <zheng.z.yan@...el.com> wrote:
>> On 06/26/2013 08:42 PM, Stephane Eranian 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.
>>
>> It's OK to have "exclude_user = exclude_kernel = 0". The LBR callstack feature is only used
>> for getting callchain of user program. If "exclude_kernel = 0", we still use frame pointer
>> to get the callchain.
>>
> And what's the point of collecting the user callstack in a case when
> the counter overflowed
> in the kernel? It won't be directly correlated to the IIP.
>
> Now this mode is useful for some other measurements, but I think you
> are after correlating
> interrupted IP with callstack.
>
If "exclude_user = exclude_kernel = 0" and "(sample_type & PERF_SAMPLE_CALLCHAIN) = true".
when the counter overflows in the kernel, perf_sample_output() writes both kernel callchain
and *user callchain* to the sample buffer.
>
>> Regards
>> Yan, Zheng
>>
>>
>>>
>>> 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;
branch_sample_type always is (PERF_SAMPLE_BRANCH_USER | PERF_SAMPLE_BRANCH_CALL_STACK)
it means the LBR stays unchanged when the CPU is in kernel mode.
Regards
Yan, Zheng
>>>> }
>>>>
>>>> /*
>>>> @@ -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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