[patch] perf_event_open.2: Clarify PERF_EVENT_IOC_REFRESH behavior

From: Vince Weaver
Date: Thu Feb 12 2015 - 12:11:31 EST

Currently the PERF_EVENT_IOC_REFRESH ioctl, when applied to a group
leader, will refresh all children. Also if a refresh value of 0
is chosen then the refresh becomes infinite (never runs out).
Back in 2011 PAPI was relying on these behaviors but I was told
that both were unsupported and subject to being removed at any time.
(See https://lkml.org/lkml/2011/5/24/337 )
However the behavior has not been changed.

This patch updates the manpage to still list the behavior as
unsupported, but removes the innacurate description of it
only being a problem with 2.6 kernels.

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

diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
index 39c8d8c..76136e2 100644
--- a/man2/perf_event_open.2
+++ b/man2/perf_event_open.2
@@ -2353,6 +2353,12 @@ once the counter reaches 0
is indicated and
the underlying event is disabled.

+Refreshing an event group leader refreshes all siblings and
+refreshing with a parameter of 0 currently enables infinite
+these behaviors are unsupported and should not be relied on.
+.\" See https://lkml.org/lkml/2011/5/24/337
Starting with Linux 3.18,
.\" commit 179033b3e064d2cd3f5f9945e76b0a0f0fbf4883
@@ -2805,11 +2811,6 @@ Prior to Linux 2.6.35,
did not work with attached processes.

-In older Linux 2.6 versions,
-refreshing an event group leader refreshed all siblings,
-and refreshing with a parameter of 0 enabled infinite refresh.
-This behavior is unsupported and should not be relied on.
There is a bug in the kernel code between
Linux 2.6.36 and Linux 3.0 that ignores the
"watermark" field and acts as if a wakeup_event

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/