From mboxrd@z Thu Jan  1 00:00:00 1970
From: mark.rutland@arm.com (Mark Rutland)
Date: Mon, 20 Jun 2016 14:44:30 +0100
Subject: [RFC PATCH] clocksource: arm_arch_timer: disable the evtstrm via
 the cmdline
In-Reply-To: <20160620133001.GE29165@arm.com>
References: <1466171011-30468-1-git-send-email-will.deacon@arm.com>
 <5766FBC6.6000405@linaro.org> <20160620082157.GC29165@arm.com>
 <5767E89F.5020809@linaro.org> <20160620133001.GE29165@arm.com>
Message-ID: <20160620134429.GB9246@leverpostej>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Mon, Jun 20, 2016 at 02:30:02PM +0100, Will Deacon wrote:
> On Mon, Jun 20, 2016 at 02:59:11PM +0200, Daniel Lezcano wrote:
> > On 06/20/2016 10:21 AM, Will Deacon wrote:
> > >On Sun, Jun 19, 2016 at 10:08:38PM +0200, Daniel Lezcano wrote:
> > >>On 06/17/2016 03:43 PM, Will Deacon wrote:
> > >>
> > >>[ Cc'ed tglx ]
> > >>
> > >>>Disabling the eventstream can be useful for debugging and development
> > >>>purposes
> > >>
> > >>If it is for debugging and development, why upstream this change ?
> > >
> > >Mainly because it's desirable to be able to debug systems remotely, on
> > >machines that you don't have direct access to and where recompiling the
> > >kernel isn't necessarily an option. There are plenty of "no*" kernel
> > >parameters already that fall into a similar category.
> > 
> > if the kernel is in development and debug, why this option can't be part of
> > debugging code ?
> > 
> > If recompiling isn't an option, how this can be for "debugging and
> > development" ?
> 
> Sorry, I wasn't very clear. The sort of use-case I'm envisaging is where
> somebody is running a distro kernel on non-public hardware and sends me an
> email about spinlock performance. Being able to disable the event stream
> easily is a powerful tool in the small box of remote debugging tools and
> would be useful in pinning down things like missing events.
> 
> So when I say "development and debug" I'm really thinking about *remote*
> debug via a user, and then potentially the subsequent development of a
> patch.

We should probably place this rationale in the commit message. e.g.
(fake emphasis):

Disabling the eventstream can be useful for *remotely* debugging *a
deployed production system*.

Mark.