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Date: Tue, 7 Oct 2014 03:00:00 +0000
From: "Liang, Kan" <kan.liang@...el.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: "eranian@...gle.com" <eranian@...gle.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"mingo@...hat.com" <mingo@...hat.com>,
"paulus@...ba.org" <paulus@...ba.org>,
"acme@...nel.org" <acme@...nel.org>,
"ak@...ux.intel.com" <ak@...ux.intel.com>,
"Yan, Zheng" <zheng.z.yan@...el.com>
Subject: RE: [PATCH V5 11/16] perf, core: Pass perf_sample_data to
perf_callchain()
> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Wednesday, September 24, 2014 10:15 AM
> To: Liang, Kan
> Cc: eranian@...gle.com; linux-kernel@...r.kernel.org; mingo@...hat.com;
> paulus@...ba.org; acme@...nel.org; ak@...ux.intel.com; Yan, Zheng
> Subject: Re: [PATCH V5 11/16] perf, core: Pass perf_sample_data to
> perf_callchain()
>
> On Wed, Sep 10, 2014 at 10:09:08AM -0400, kan.liang@...el.com wrote:
> > From: Kan Liang <kan.liang@...el.com>
> >
> > Haswell has a new feature that utilizes the existing Last Branch
> > Record facility to record call chains. When the feature is enabled,
> > function call will be collected as normal, but as return instructions
> > are executed the last captured branch record is popped from the
> > on-chip LBR registers.
> > The LBR call stack facility can help perf to get call chains of progam
> > without frame pointer.
> >
> > This patch modifies various architectures' perf_callchain() to accept
> > perf sample data. Later patch will add code that use the sample data
> > to get call chains.
>
> So I don't like this. Why not use the regular PERF_SAMPLE_BRANCH_STACK
> output to generate the stuff from? We already have two different means,
> with different transport, for callchains anyhow, so a third really won't matter.
I'm not sure what you mean by using the regular PERF_SAMPLE_BRANCH_STACK output to generate the stuff from.
But we don't need to modify various architectures' perf_callchain_user, if that's your concern.
An alternative way is to generate the callchain output in a higher level, like perf_callchain.
If there is no frame pointer, the entry->nr will be set to MAX+1. So the perf_callchain knows that we need to try LBR callstack if possible.
In perf_callchain, it resets entry->nr to old value, and call perf_callchain_lbr_callstack to check and fill the callchain struct if possible.
The patch is as below.
What do you think?
diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index f2a88de..677f8af 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -156,11 +156,28 @@ put_callchain_entry(int rctx)
put_recursion_context(__get_cpu_var(callchain_recursion), rctx);
}
+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) {
+ int i = 0;
+ while (i < br_stack->nr && entry->nr < PERF_MAX_STACK_DEPTH) {
+ perf_callchain_store(entry, br_stack->entries[i].from);
+ i++;
+ }
+ }
+}
+
struct perf_callchain_entry *
-perf_callchain(struct perf_event *event, struct pt_regs *regs)
+perf_callchain(struct perf_event *event, struct pt_regs *regs,
+ struct perf_sample_data *data)
{
int rctx;
struct perf_callchain_entry *entry;
+ __u64 old_nr;
int kernel = !event->attr.exclude_callchain_kernel;
int user = !event->attr.exclude_callchain_user;
@@ -198,7 +215,13 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs)
goto exit_put;
perf_callchain_store(entry, PERF_CONTEXT_USER);
+ old_nr = entry->nr;
perf_callchain_user(entry, regs);
+ if (entry->nr == (PERF_MAX_STACK_DEPTH + 1)) {
+ entry->nr = old_nr;
+ perf_callchain_lbr_callstack(entry, data);
+ } else
+ entry->nr = old_nr;
}
}
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 185fa03..0439c8f 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -2061,6 +2061,15 @@ 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);
}
+
+ /*
+ * try LBR callstack if there is no frame pointer
+ * Set entry->nr to MAX + 1 to notify the perf_callchain.
+ * perf_callchain finally try LBR callstack and reset entry->nr
+ */
+ if (fp == compat_ptr(regs->bp))
+ entry->nr = PERF_MAX_STACK_DEPTH + 1;
+
return 1;
}
#else
@@ -2113,6 +2122,14 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
perf_callchain_store(entry, frame.return_address);
fp = frame.next_frame;
}
+
+ /*
+ * try LBR callstack if there is no frame pointer
+ * Set entry->nr to MAX + 1 to notify the perf_callchain.
+ * perf_callchain finally try LBR callstack and reset entry->nr
+ */
+ if (fp == (void __user *)regs->bp)
+ entry->nr = PERF_MAX_STACK_DEPTH + 1;
}
/*
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 50bb51d..2808267 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1533,7 +1533,7 @@ again:
perf_sample_data_init(&data, 0, event->hw.last_period);
- if (has_branch_stack(event))
+ if (needs_branch_stack(event))
data.br_stack = &cpuc->lbr_stack;
if (perf_event_overflow(event, &data, regs))
diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index 8e6c88f..6c995b7 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -758,6 +758,8 @@ 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;
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 285776a..84840cc 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -75,6 +75,7 @@ struct perf_raw_record {
* recent branch.
*/
struct perf_branch_stack {
+ bool user_callstack;
__u64 nr;
struct perf_branch_entry entries[0];
};
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4dd5700..825b487 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4915,7 +4915,7 @@ void perf_prepare_sample(struct perf_event_header *header,
if (sample_type & PERF_SAMPLE_CALLCHAIN) {
int size = 1;
- data->callchain = perf_callchain(event, regs);
+ data->callchain = perf_callchain(event, regs, data);
if (data->callchain)
size += data->callchain->nr;
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index 569b2187..3a0239e 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -147,7 +147,8 @@ DEFINE_OUTPUT_COPY(__output_copy_user, arch_perf_out_copy_user)
/* Callchain handling */
extern struct perf_callchain_entry *
-perf_callchain(struct perf_event *event, struct pt_regs *regs);
+perf_callchain(struct perf_event *event, struct pt_regs *regs,
+ struct perf_sample_data *data);
extern int get_callchain_buffers(void);
extern void put_callchain_buffers(void);
--
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