linux-kernel - Re: [PATCH 1/2] perf tools: fix a typo of a Power7 event name

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Date:	Wed, 19 Jun 2013 19:28:37 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Michael Ellerman <michael@...erman.id.au>
Cc:	Runzhen Wang <runzhen@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	paulus@...ba.org, acme@...hat.com,
	xiaoguangrong@...ux.vnet.ibm.com, icycoder@...il.com
Subject: Re: [PATCH 1/2] perf tools: fix a typo of a Power7 event name

Michael Ellerman [michael@...erman.id.au] wrote:
| On Wed, 2013-06-19 at 17:15 +0800, Runzhen Wang wrote:
| > In the Power7 PMU guide:
| > https://www.power.org/documentation/commonly-used-metrics-for-performance-analysis/
| > PM_BRU_MPRED is referred to as PM_BR_MPRED.
| > 
| > This patch fix the typo by changing the name of the event in kernel and
| > documentation accordingly.
| > 
| > Signed-off-by: Runzhen Wang <runzhen@...ux.vnet.ibm.com>
| > ---
| >  .../testing/sysfs-bus-event_source-devices-events  |    2 +-
| >  arch/powerpc/perf/power7-pmu.c                     |   12 ++++++------
| >  2 files changed, 7 insertions(+), 7 deletions(-)
| > 
| > diff --git a/Documentation/ABI/testing/sysfs-bus-event_source-devices-events b/Documentation/ABI/testing/sysfs-bus-event_source-devices-events
| > index 8b25ffb..3c1cc24 100644
| > --- a/Documentation/ABI/testing/sysfs-bus-event_source-devices-events
| > +++ b/Documentation/ABI/testing/sysfs-bus-event_source-devices-events
| > @@ -29,7 +29,7 @@ Description:	Generic performance monitoring events
| >  
| >  What: 		/sys/devices/cpu/events/PM_1PLUS_PPC_CMPL
| >  		/sys/devices/cpu/events/PM_BRU_FIN
| > -		/sys/devices/cpu/events/PM_BRU_MPRED
| > +		/sys/devices/cpu/events/PM_BR_MPRED
| 
| So you're changing the ABI.
| 
| I think that's probably OK, but you at least need to mention _why_ you
| think it's OK.

Some of the reasons I think its ok to change:

- It is relatively new interface, specific to the Power7 platform.

- No tools that we know of actually use this interface at this point (none
  are listed near the interface).

- Users of this interface (eg oprofile users migrating to perf) would be
  more used to the "PM_BR_MPRED" rather than "PM_BRU_MPRED".

- These are in the ABI/testing at this point rather than ABI/stable, so
  hoping we have some wiggle room.

But of course this is not a "grave error" or "security hole" which are
the justifications listed in the Documentation/ABI/README.  If these
are not good enough reasons, we can leave the misnomer around and
create another file in sysfs with the correct name PM_BR_MPRED.

Sukadev

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