[patch] perf_event_open.2: sample_max_stack support

From: Vince Weaver
Date: Thu Oct 13 2016 - 17:18:09 EST

Linux 4.8 added a new sample_max_stack parameter, as well as
/proc/sys/kernel/perf_event_max_stack which limits it and a new
EOVERFLOW error return.

Signed-off-by: Vince Weaver <vincent.weaver@xxxxxxxxx>

diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
index 3c894cc..edfdb72 100644
--- a/man2/perf_event_open.2
+++ b/man2/perf_event_open.2
@@ -268,7 +268,8 @@ struct perf_event_attr {
__s32 clockid; /* clock to use for time fields */
__u64 sample_regs_intr; /* regs to dump on samples */
__u32 aux_watermark; /* aux bytes before wakeup */
- __u32 __reserved_2; /* align to u64 */
+ __u16 sample_max_stack; /* max frames in callchain */
+ __u16 __reserved_2; /* align to u64 */

@@ -1307,6 +1308,15 @@ currently supported.
This specifies how much data is required to trigger a
+.IR "sample_max_stack" " (since Linux 4.8)"
+.\" commit 97c79a38cd454602645f0470ffb444b3b75ce574
+.I sample_type
+this specifies how many stack frames to report when
+generating the callchain.
.SS Reading results
Once a
.BR perf_event_open ()
@@ -2780,6 +2790,14 @@ users to sample at a rate that impacts overall machine performance
and potentially lock up the machine.
The default value is
100000 (samples per second).
+.I /proc/sys/kernel/perf_event_max_stack
+.\" Introduced in c5dfd78eb79851e278b7973031b9ca363da87a7e
+This sets the maximum depth of stack frame entries reported
+when generating a call trace.
.I /proc/sys/kernel/perf_event_mlock_kb

@@ -3001,6 +3019,15 @@ This includes requesting low-skid events if not supported,
branch tracing if it is not available, sampling if no PMU
interrupt is available, and branch stacks for software events.
+.BR EOVERFLOW " (since Linux 4.8)"
+.\" 97c79a38cd454602645f0470ffb444b3b75ce574
+Returned if
+is requested and
+.I sample_max_stack
+is larger than the maximum specified in
+.IR /proc/sys/kernel/perf_event_max_stack .
Returned on many (but not all) architectures when an unsupported
.IR exclude_hv ", " exclude_idle ", " exclude_user ", or " exclude_kernel