From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vw0-f51.google.com (mail-vw0-f51.google.com [209.85.212.51]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id 9EFF5B6F12 for ; Thu, 31 Mar 2011 05:37:05 +1100 (EST) Received: by vws20 with SMTP id 20so1375029vws.38 for ; Wed, 30 Mar 2011 11:37:01 -0700 (PDT) Date: Wed, 30 Mar 2011 14:36:56 -0400 From: Eric B Munson To: Benjamin Herrenschmidt Subject: Re: [PATCH] POWER: perf_event: Skip updating kernel counters if register value shrinks Message-ID: <20110330183656.GA2564@mgebm.net> References: <1301059689-4556-1-git-send-email-emunson@mgebm.net> <1301378637.2402.671.camel@pasglop> <20110329142519.GA3527@mgebm.net> <1301433165.2402.689.camel@pasglop> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="EVF5PPMfhYS0aIcm" In-Reply-To: <1301433165.2402.689.camel@pasglop> Cc: a.p.zijlstra@chello.nl, linux-kernel@vger.kernel.org, paulus@samba.org, anton@samba.org, acme@ghostprotocols.net, mingo@elte.hu, linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , --EVF5PPMfhYS0aIcm Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, 30 Mar 2011, Benjamin Herrenschmidt wrote: > On Tue, 2011-03-29 at 10:25 -0400, Eric B Munson wrote: > > Here I made the assumption that the hardware would never remove more ev= ents in > > a speculative roll back than it had added. This is not a situation I > > encoutered in my limited testing, so I didn't think underflow was possi= ble. I > > will send out a V2 using the signed 32 bit delta and remeber to CC stab= le > > this time.=20 >=20 > I'm not thinking about underflow but rollover... or that isn't possible > with those counters ? IE. They don't wrap back to 0 after hitting > ffffffff ? >=20 They do roll over to 0 after ffffffff, but I thought that case was already covered by the perf_event_interrupt. Are you concerned that we will reset a counter and speculative roll back will underflow that counter? --EVF5PPMfhYS0aIcm Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iQEcBAEBAgAGBQJNk3hIAAoJEH65iIruGRnNsUwH/3qT728+BEeypqHDAYtS6Vxt vrLNmiVCOjkBvek7FvXdmGmK2hlqj/fziTA9UCN5Z84Bm170X4R+PJFLeDBHfJSt kcJVVw/TwQlmUu+E7K6tg1LRt0mfxeh/JvxhZylW3XlCNyL0xvs8PLtc5anbThDL bi52mX7vbZLJxb+5ESLP71WmGYJ5K4ldLKH2BiwzEmXc8a1XhHmM6bmsh4qBL5pg 4Z4vTn+KB+L1JpYj6OVMYynmZtxx8/H1eRPSyVPVloQy9Ty3RzaUnpiqo46Autwc 2a2hYuDtk9Uq8Z1Ru75UVZI4cW838VmikMBOaZmRzMaSdIt/uCwlJQiLxGDYXpY= =dnjq -----END PGP SIGNATURE----- --EVF5PPMfhYS0aIcm--