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Subject[tip:perf/hw-branch-sampling] perf: Add generic taken branch sampling support
Commit-ID:  bce38cd53e5ddba9cb6d708c4ef3d04a4016ec7e
Gitweb: http://git.kernel.org/tip/bce38cd53e5ddba9cb6d708c4ef3d04a4016ec7e
Author: Stephane Eranian <eranian@google.com>
AuthorDate: Thu, 9 Feb 2012 23:20:51 +0100
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Mon, 5 Mar 2012 14:55:39 +0100

perf: Add generic taken branch sampling support

This patch adds the ability to sample taken branches to the
perf_event interface.

The ability to capture taken branches is very useful for all
sorts of analysis. For instance, basic block profiling, call
counts, statistical call graph.

This new capability requires hardware assist and as such may
not be available on all HW platforms. On Intel x86 it is
implemented on top of the Last Branch Record (LBR) facility.

To enable taken branches sampling, the PERF_SAMPLE_BRANCH_STACK
bit must be set in attr->sample_type.

Sampled taken branches may be filtered by type and/or priv
levels.

The patch adds a new field, called branch_sample_type, to the
perf_event_attr structure. It contains a bitmask of filters
to apply to the sampled taken branches.

Filters may be implemented in HW. If the HW filter does not exist
or is not good enough, some arch may also implement a SW filter.

The following generic filters are currently defined:
- PERF_SAMPLE_USER
only branches whose targets are at the user level

- PERF_SAMPLE_KERNEL
only branches whose targets are at the kernel level

- PERF_SAMPLE_HV
only branches whose targets are at the hypervisor level

- PERF_SAMPLE_ANY
any type of branches (subject to priv levels filters)

- PERF_SAMPLE_ANY_CALL
any call branches (may incl. syscall on some arch)

- PERF_SAMPLE_ANY_RET
any return branches (may incl. syscall returns on some arch)

- PERF_SAMPLE_IND_CALL
indirect call branches

Obviously filter may be combined. The priv level bits are optional.
If not provided, the priv level of the associated event are used. It
is possible to collect branches at a priv level different from the
associated event. Use of kernel, hv priv levels is subject to permissions
and availability (hv).

The number of taken branch records present in each sample may vary based
on HW, the type of sampled branches, the executed code. Therefore
each sample contains the number of taken branches it contains.

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1328826068-11713-2-git-send-email-eranian@google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
arch/x86/kernel/cpu/perf_event_intel_lbr.c | 21 +++++---
include/linux/perf_event.h | 71 ++++++++++++++++++++++++++--
kernel/events/core.c | 68 ++++++++++++++++++++++++++
3 files changed, 148 insertions(+), 12 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index 47a7e63..309d0cc 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -142,9 +142,11 @@ static void intel_pmu_lbr_read_32(struct cpu_hw_events *cpuc)

rdmsrl(x86_pmu.lbr_from + lbr_idx, msr_lastbranch.lbr);

- cpuc->lbr_entries[i].from = msr_lastbranch.from;
- cpuc->lbr_entries[i].to = msr_lastbranch.to;
- cpuc->lbr_entries[i].flags = 0;
+ cpuc->lbr_entries[i].from = msr_lastbranch.from;
+ cpuc->lbr_entries[i].to = msr_lastbranch.to;
+ cpuc->lbr_entries[i].mispred = 0;
+ cpuc->lbr_entries[i].predicted = 0;
+ cpuc->lbr_entries[i].reserved = 0;
}
cpuc->lbr_stack.nr = i;
}
@@ -165,19 +167,22 @@ static void intel_pmu_lbr_read_64(struct cpu_hw_events *cpuc)

for (i = 0; i < x86_pmu.lbr_nr; i++) {
unsigned long lbr_idx = (tos - i) & mask;
- u64 from, to, flags = 0;
+ u64 from, to, mis = 0, pred = 0;

rdmsrl(x86_pmu.lbr_from + lbr_idx, from);
rdmsrl(x86_pmu.lbr_to + lbr_idx, to);

if (lbr_format == LBR_FORMAT_EIP_FLAGS) {
- flags = !!(from & LBR_FROM_FLAG_MISPRED);
+ mis = !!(from & LBR_FROM_FLAG_MISPRED);
+ pred = !mis;
from = (u64)((((s64)from) << 1) >> 1);
}

- cpuc->lbr_entries[i].from = from;
- cpuc->lbr_entries[i].to = to;
- cpuc->lbr_entries[i].flags = flags;
+ cpuc->lbr_entries[i].from = from;
+ cpuc->lbr_entries[i].to = to;
+ cpuc->lbr_entries[i].mispred = mis;
+ cpuc->lbr_entries[i].predicted = pred;
+ cpuc->lbr_entries[i].reserved = 0;
}
cpuc->lbr_stack.nr = i;
}
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 64426b7..5fc494f 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -129,11 +129,40 @@ enum perf_event_sample_format {
PERF_SAMPLE_PERIOD = 1U << 8,
PERF_SAMPLE_STREAM_ID = 1U << 9,
PERF_SAMPLE_RAW = 1U << 10,
+ PERF_SAMPLE_BRANCH_STACK = 1U << 11,

- PERF_SAMPLE_MAX = 1U << 11, /* non-ABI */
+ PERF_SAMPLE_MAX = 1U << 12, /* non-ABI */
};

/*
+ * values to program into branch_sample_type when PERF_SAMPLE_BRANCH is set
+ *
+ * If the user does not pass priv level information via branch_sample_type,
+ * the kernel uses the event's priv level. Branch and event priv levels do
+ * not have to match. Branch priv level is checked for permissions.
+ *
+ * The branch types can be combined, however BRANCH_ANY covers all types
+ * of branches and therefore it supersedes all the other types.
+ */
+enum perf_branch_sample_type {
+ PERF_SAMPLE_BRANCH_USER = 1U << 0, /* user branches */
+ PERF_SAMPLE_BRANCH_KERNEL = 1U << 1, /* kernel branches */
+ PERF_SAMPLE_BRANCH_HV = 1U << 2, /* hypervisor branches */
+
+ PERF_SAMPLE_BRANCH_ANY = 1U << 3, /* any branch types */
+ PERF_SAMPLE_BRANCH_ANY_CALL = 1U << 4, /* any call branch */
+ PERF_SAMPLE_BRANCH_ANY_RETURN = 1U << 5, /* any return branch */
+ PERF_SAMPLE_BRANCH_IND_CALL = 1U << 6, /* indirect calls */
+
+ PERF_SAMPLE_BRANCH_MAX = 1U << 7, /* non-ABI */
+};
+
+#define PERF_SAMPLE_BRANCH_PLM_ALL \
+ (PERF_SAMPLE_BRANCH_USER|\
+ PERF_SAMPLE_BRANCH_KERNEL|\
+ PERF_SAMPLE_BRANCH_HV)
+
+/*
* The format of the data returned by read() on a perf event fd,
* as specified by attr.read_format:
*
@@ -240,6 +269,7 @@ struct perf_event_attr {
__u64 bp_len;
__u64 config2; /* extension of config1 */
};
+ __u64 branch_sample_type; /* enum branch_sample_type */
};

/*
@@ -458,6 +488,8 @@ enum perf_event_type {
*
* { u32 size;
* char data[size];}&& PERF_SAMPLE_RAW
+ *
+ * { u64 from, to, flags } lbr[nr];} && PERF_SAMPLE_BRANCH_STACK
* };
*/
PERF_RECORD_SAMPLE = 9,
@@ -530,12 +562,34 @@ struct perf_raw_record {
void *data;
};

+/*
+ * single taken branch record layout:
+ *
+ * from: source instruction (may not always be a branch insn)
+ * to: branch target
+ * mispred: branch target was mispredicted
+ * predicted: branch target was predicted
+ *
+ * support for mispred, predicted is optional. In case it
+ * is not supported mispred = predicted = 0.
+ */
struct perf_branch_entry {
- __u64 from;
- __u64 to;
- __u64 flags;
+ __u64 from;
+ __u64 to;
+ __u64 mispred:1, /* target mispredicted */
+ predicted:1,/* target predicted */
+ reserved:62;
};

+/*
+ * branch stack layout:
+ * nr: number of taken branches stored in entries[]
+ *
+ * Note that nr can vary from sample to sample
+ * branches (to, from) are stored from most recent
+ * to least recent, i.e., entries[0] contains the most
+ * recent branch.
+ */
struct perf_branch_stack {
__u64 nr;
struct perf_branch_entry entries[0];
@@ -566,7 +620,9 @@ struct hw_perf_event {
unsigned long event_base;
int idx;
int last_cpu;
+
struct hw_perf_event_extra extra_reg;
+ struct hw_perf_event_extra branch_reg;
};
struct { /* software */
struct hrtimer hrtimer;
@@ -1007,12 +1063,14 @@ struct perf_sample_data {
u64 period;
struct perf_callchain_entry *callchain;
struct perf_raw_record *raw;
+ struct perf_branch_stack *br_stack;
};

static inline void perf_sample_data_init(struct perf_sample_data *data, u64 addr)
{
data->addr = addr;
data->raw = NULL;
+ data->br_stack = NULL;
}

extern void perf_output_sample(struct perf_output_handle *handle,
@@ -1151,6 +1209,11 @@ extern void perf_bp_event(struct perf_event *event, void *data);
# define perf_instruction_pointer(regs) instruction_pointer(regs)
#endif

+static inline bool has_branch_stack(struct perf_event *event)
+{
+ return event->attr.sample_type & PERF_SAMPLE_BRANCH_STACK;
+}
+
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 e8b32ac..5820efd 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -118,6 +118,13 @@ static int cpu_function_call(int cpu, int (*func) (void *info), void *info)
PERF_FLAG_FD_OUTPUT |\
PERF_FLAG_PID_CGROUP)

+/*
+ * branch priv levels that need permission checks
+ */
+#define PERF_SAMPLE_BRANCH_PERM_PLM \
+ (PERF_SAMPLE_BRANCH_KERNEL |\
+ PERF_SAMPLE_BRANCH_HV)
+
enum event_type_t {
EVENT_FLEXIBLE = 0x1,
EVENT_PINNED = 0x2,
@@ -3907,6 +3914,24 @@ void perf_output_sample(struct perf_output_handle *handle,
}
}
}
+
+ if (sample_type & PERF_SAMPLE_BRANCH_STACK) {
+ if (data->br_stack) {
+ size_t size;
+
+ size = data->br_stack->nr
+ * sizeof(struct perf_branch_entry);
+
+ perf_output_put(handle, data->br_stack->nr);
+ perf_output_copy(handle, data->br_stack->entries, size);
+ } else {
+ /*
+ * we always store at least the value of nr
+ */
+ u64 nr = 0;
+ perf_output_put(handle, nr);
+ }
+ }
}

void perf_prepare_sample(struct perf_event_header *header,
@@ -3949,6 +3974,15 @@ void perf_prepare_sample(struct perf_event_header *header,
WARN_ON_ONCE(size & (sizeof(u64)-1));
header->size += size;
}
+
+ if (sample_type & PERF_SAMPLE_BRANCH_STACK) {
+ int size = sizeof(u64); /* nr */
+ if (data->br_stack) {
+ size += data->br_stack->nr
+ * sizeof(struct perf_branch_entry);
+ }
+ header->size += size;
+ }
}

static void perf_event_output(struct perf_event *event,
@@ -5935,6 +5969,40 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
if (attr->read_format & ~(PERF_FORMAT_MAX-1))
return -EINVAL;

+ if (attr->sample_type & PERF_SAMPLE_BRANCH_STACK) {
+ u64 mask = attr->branch_sample_type;
+
+ /* only using defined bits */
+ if (mask & ~(PERF_SAMPLE_BRANCH_MAX-1))
+ return -EINVAL;
+
+ /* at least one branch bit must be set */
+ if (!(mask & ~PERF_SAMPLE_BRANCH_PLM_ALL))
+ return -EINVAL;
+
+ /* kernel level capture: check permissions */
+ if ((mask & PERF_SAMPLE_BRANCH_PERM_PLM)
+ && perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
+ return -EACCES;
+
+ /* propagate priv level, when not set for branch */
+ if (!(mask & PERF_SAMPLE_BRANCH_PLM_ALL)) {
+
+ /* exclude_kernel checked on syscall entry */
+ if (!attr->exclude_kernel)
+ mask |= PERF_SAMPLE_BRANCH_KERNEL;
+
+ if (!attr->exclude_user)
+ mask |= PERF_SAMPLE_BRANCH_USER;
+
+ if (!attr->exclude_hv)
+ mask |= PERF_SAMPLE_BRANCH_HV;
+ /*
+ * adjust user setting (for HW filter setup)
+ */
+ attr->branch_sample_type = mask;
+ }
+ }
out:
return ret;


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