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 <[email protected]>
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
+refreshes;
+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
.B POLL_HUP
@@ -2805,11 +2811,6 @@ Prior to Linux 2.6.35,
.B PERF_FORMAT_GROUP
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
On 02/12/2015 06:14 PM, Vince Weaver wrote:
>
> 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.
Thanks, Vince. Applied.
Cheers,
Michael
> 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 <[email protected]>
>
> 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
> +refreshes;
> +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
> .B POLL_HUP
> @@ -2805,11 +2811,6 @@ Prior to Linux 2.6.35,
> .B PERF_FORMAT_GROUP
> 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
>
>
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/