Date: Wed, 10 Dec 2008 12:48:24 +0900
From: Paul Mundt <lethal@linux-sh.org>
To: David Miller <davem@davemloft.net>
Cc: andi@firstfloor.org, mingo@elte.hu, a.p.zijlstra@chello.nl,
       paulus@samba.org, tglx@linutronix.de, linux-kernel@vger.kernel.org,
       linux-arch@vger.kernel.org, akpm@linux-foundation.org,
       eranian@googlemail.com, dada1@cosmosbay.com, robert.richter@amd.com,
       arjan@infradead.org, hpa@zytor.com, rostedt@goodmis.org
Subject: Re: [patch 0/3] [Announcement] Performance Counters for Linux
Message-ID: <20081210034824.GA27217@linux-sh.org>
Mail-Followup-To: Paul Mundt <lethal@linux-sh.org>,
	David Miller <davem@davemloft.net>, andi@firstfloor.org,
	mingo@elte.hu, a.p.zijlstra@chello.nl, paulus@samba.org,
	tglx@linutronix.de, linux-kernel@vger.kernel.org,
	linux-arch@vger.kernel.org, akpm@linux-foundation.org,
	eranian@googlemail.com, dada1@cosmosbay.com, robert.richter@amd.com,
	arjan@infradead.org, hpa@zytor.com, rostedt@goodmis.org
References: <20081205.002701.172921476.davem@davemloft.net> <20081205084233.GE2030@elte.hu> <87ej0mx0c0.fsf@basil.nowhere.org> <20081205.120814.51226316.davem@davemloft.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20081205.120814.51226316.davem@davemloft.net>
User-Agent: Mutt/1.5.13 (2006-08-11)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1530
Lines: 31

On Fri, Dec 05, 2008 at 12:08:14PM -0800, David Miller wrote:
> From: Andi Kleen <andi@firstfloor.org>
> Date: Fri, 05 Dec 2008 13:39:43 +0100
> 
> > Given these are more obscure features, but not being able to fit
> > them easily into your model from the start isn't a very promising sign
> > for the long term extensibility of the design.
> 
> Another thing I'm interested in is if this new stuff will work with
> performance counters that lack an overflow interrupt.
> 
> We have several chips that are like this, and perfmon supported that
> on the kernel side, and also provided overflow emulation for such
> hardware in userspace (where such complexity belongs).

There doesn't seem to have been any reply to this point unfortunately,
and it is something I am also wondering about.

The sh perf counters were not designed with overflowing in mind, they are
split in to a pair of 48-bit or 64-bit counters that simply keep running.
Any write simply clears the value and the counter starts over. They are
simply counters only, and generate no events whatsoever.

Oprofile has been a pretty bad fit for them, and while I'm slightly more
optimistic about perfmon, I'm rather less enthusiastic about yet another
peformance counter implementation that I am unable to make any use of. 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/