From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=90.155.92.199 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793353197; b=Kc9nT73WeueoHGHsMqCtEIGafCwgefXAUobLhVo3Lns7P9qVMC6y/wwR1ubLkC1Ay1rZ mV1A8PPUyJAjylBDOJA+uW6MsiVMSckfMCqjQl7RGhrdUf106Dlm4V1pVFcrBkZD69PNv EQl1QBvKQAVD24dNyVnoNi+nqPc7GSixsaANYe0zr88YEjBKL418FoW/pTsnRgozwUED1 /jOQVOjv113JXHHMG1rMlygdi94G0No7+Dn4BU/gJRv2zgGdH4z1kIouFDv/Tcu5mris9 QvLgzVFi1XQULmMoCSKkaEs/6GLwjW9eocYqkLmRgmH2g5fjZmP1i3TTMASnj7j9SJw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793353197; h=DMARC-Filter:DKIM-Signature:Received:Received:Date:From:To:Cc: Subject:Message-ID:References:MIME-Version:Content-Type: Content-Disposition:Content-Transfer-Encoding:In-Reply-To; bh=tPNvnOFWbZg4adT62qnCH63S50YUPovaQONoc9l3558=; b=wxy7NvNYFKsZnXOou5G7jq3x1VM4s2RciRqmtnAAljnaX3YxFzoXqJ/mhH8aiNaS7+8y nO+HkzfM6YlzMLLJin7RISa/ExqDVxAXBoR2iPc3Abcfv32meSt/bUV+Cl70HgW0AlrqQ e45DW9rT7JBnb66RogccHncOqSr/VfaANmQm/SWoWE8dOICHVxI6VIbXFGloGWe8JApHZ mBZqOJg8verpFdj8G4pxDHCxpfy266oAeNEFq24pm+iseAUjS5heRRI3T4+goww85HS9X 3NDWzKImx2hLU6sTri9+3uARdx43svCgxaHbNv+gTxsnFMJH0om99prWVXv0B9rp+KQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=desiato.20200630 header.b=UlcnXyOh; arc=none smtp.remote-ip=90.155.92.199 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3FC92606A31E; Fri, 30 Oct 2026 09:39:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 3FC92606A31E Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=desiato.20200630 header.b=UlcnXyOh DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=tPNvnOFWbZg4adT62qnCH63S50YUPovaQONoc9l3558=; b=UlcnXyOhb8vMMu7SJFoA+h3+Kv rETEph2rrkw1yEe+u3qNItK43aC6/4pQLjQHYnPF4KhxpadkFyOxImJRdlgb2UcygTB/BBjwg+Qgl /DQdo+uQLg+c41LS2tNd5td/vqMj97NWcq3qyZpstr6AAcfb1vTtfNBCn7hBSazmpThim+9fEfJAn nix4lkqMuDfbVRapYe3qo6vyIL/L9A3dLb8Ur3KS8hif1HF4OlSPnWbaxba5yGhI09e+Th52MPDQm Aw2Tqrucpt4uM+d9KKdD7s1KicIac3tnzY8NYREs1LV6xtV2uQF4UORmqBQxFB0y8VbgyCIqTwMk7 fQj/DdJA==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.100.1 #2 (Red Hat Linux)) id 1xMj5T-00000000BYM-197f; Fri, 30 Oct 2026 09:39:51 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 621D9300578; Fri, 30 Oct 2026 10:39:50 +0100 (CET) Date: Fri, 30 Oct 2026 10:39:50 +0100 From: Peter Zijlstra To: Matt Turner Cc: Richard Henderson , Magnus Lindholm , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org Subject: Re: [PATCH 0/5] alpha/perf: add ProfileMe sampling Message-ID: <20261030093950.GI2668200@noisy.programming.kicks-ass.net> References: <20261028-alpha-profileme-v1-0-d44b52bf2500@gmail.com> <20261029091141.GG1779021@noisy.programming.kicks-ass.net> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Fri, Oct 30, 2026 at 12:00:41AM -0400, Matt Turner wrote: > On Thu, Oct 29, 2026 at 11:34 AM Matt Turner wrote: > > > > On Thu, Oct 29, 2026 at 5:11 AM Peter Zijlstra wrote: > > > > > > On Wed, Oct 28, 2026 at 02:09:29PM -0400, Matt Turner wrote: > > > > The 21264 from EV67 on, and the 21364, have a second performance counter > > > > mode, ProfileMe, alongside the Aggregate mode that the driver uses today. > > > > An Aggregate mode sample reports the PC where the overflow interrupt was > > > > taken. On an EV7 that is anywhere from 15 instructions before to 12 > > > > after the one that overflowed the counter, which makes perf annotate > > > > output close to useless. In ProfileMe mode the CPU picks one fetched > > > > instruction, follows it down the pipeline, and reports its PC along with > > > > what happened to it: whether it retired, whether it trapped and why, > > > > whether it was a mispredicted branch, stalled before map, or was killed > > > > on a wrong path, and what PCTR1 counted while it was in flight. > > > > > > Isn't this the thing that ended up as AMD's IBS? > > > > I have no idea, but it wouldn't surprise me too much :) > > Looking a bit further, it does seem so. ProfileMe was published by Dean > et al. at MICRO-30 in 1997, and IBS works the same way: tag one > instruction, follow it down the pipeline, and report what happened to > it. Right, I thought I remembered something like that. Anyway, I was thinking that perhaps there was something to share with the existing IBS work, but the AI overlords abused me of that idea quite quickly. While they are very similar in spirit, they are very distinct in practice. Carry on the legacy compute :-)