From: Scott Wood <scottwood@freescale•com>
To: Jerry Van Baren <gvb.linuxppc.dev@gmail•com>
Cc: linuxppc-dev list <linuxppc-dev@ozlabs•org>,
Phillips Kim <Kim.Phillips@freescale•com>,
Paul Mackerras <paulus@samba•org>
Subject: Re: [PATCH v2] Make 83xx perfmon support selectable
Date: Fri, 21 Mar 2008 11:24:01 -0500 [thread overview]
Message-ID: <20080321162401.GB4170@loki.buserror.net> (raw)
In-Reply-To: <47E2FA6D.9020200@gmail.com>
On Thu, Mar 20, 2008 at 07:59:41PM -0400, Jerry Van Baren wrote:
> Per Andy (and my limited reading of the UMs), some 83xx have the PMR
> registers and some don't. The compiler either supports the PMR register
> or it doesn't. If you make it runtime configurable, people running CPUs
> that don't support the specific PMR will have to change compiler
> configurations in order to compile with the PMR register in there (could
> have unintended consequences).
I'm not saying make it runtime-only -- you can still have a config option to
determine whether to build a kernel that supports it. I'm saying there
should be an additional runtime check so that if you run a multiplatform
kernel with perfmon enabled on a chip that doesn't support it, you won't
take a program check.
> Also, if you look at the code (arch/powerpc/kernel/pmc.c), there are
> several different types of PMR registers, based on the core and flavor
> of the core. Finding or making a compiler setup that supports all of
> the possible PMR registers could be a problem.
It only needs to support all possible registers within a class of hardware
over which we support multiplatform kernels.
> You would still have to make the PMR read/write runtime selectable
> because the CPUs that don't support that register will raise an
> exception IIRC (an Really Bad Thing[tm]).
Yes, that was my point. The changelog on the patch seemed to indicate that
the compile-time option was intended to address this, not just the toolchain
problem.
-Scott
prev parent reply other threads:[~2008-03-21 16:24 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-03-07 23:59 [PATCH v2] Make 83xx perfmon support selectable Andy Fleming
2008-03-08 13:26 ` Jerry Van Baren
2008-03-10 14:39 ` Kumar Gala
2008-03-18 17:05 ` Scott Wood
2008-03-19 23:48 ` Kumar Gala
2008-03-20 23:59 ` Jerry Van Baren
2008-03-21 16:24 ` Scott Wood [this message]
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