Date: Wed, 30 Nov 2005 01:34:33 +0100
From: Andi Kleen <ak@suse.de>
To: David Gibson <david@gibson.dropbear.id.au>, Andi Kleen <ak@suse.de>,
       Nicholas Miell <nmiell@comcast.net>,
       Stephane Eranian <eranian@hpl.hp.com>,
       Ray Bryant <raybry@mpdtxmail.amd.com>, discuss@x86-64.org,
       linux-kernel@vger.kernel.org, perfctr-devel@lists.sourceforge.net
Subject: Re: [Perfctr-devel] Re: Enabling RDPMC in user space by default
Message-ID: <20051130003433.GA19515@wotan.suse.de>
References: <20051129181344.GN19515@wotan.suse.de> <1133300591.3271.1.camel@entropy> <20051129215207.GR19515@wotan.suse.de> <1133303615.3271.12.camel@entropy> <20051129224346.GS19515@wotan.suse.de> <1133305338.3271.30.camel@entropy> <20051129231750.GU19515@wotan.suse.de> <1133306966.3271.36.camel@entropy> <20051129233920.GW19515@wotan.suse.de> <20051129235626.GC9659@localhost.localdomain>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20051129235626.GC9659@localhost.localdomain>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 921
Lines: 22

On Wed, Nov 30, 2005 at 10:56:26AM +1100, David Gibson wrote:
> On Wed, Nov 30, 2005 at 12:39:20AM +0100, Andi Kleen wrote:
> > > Well, if that's all you want them to use RDPMC 0 for, why not just make
> > > PMCs programmable from userspace?
> > 
> > First we need to have a cycle counter PMC anyways for the NMI watchdog.
> > So it can as well be used for other purposes.
> 
> But the watchdog doesn't require it to be in the same place on all
> machines.  Exporting it turns an internal requirement into an ABI
> point.

Yes, but the only alternative I know of would be to let user space
continue getting broken all the time with RDTSC.  RDPMC is a nice
alternative. 

-Andi
-
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/