From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753968AbbJPLvP (ORCPT ); Fri, 16 Oct 2015 07:51:15 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:38274 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752772AbbJPLvO (ORCPT ); Fri, 16 Oct 2015 07:51:14 -0400 Date: Fri, 16 Oct 2015 13:51:07 +0200 From: Peter Zijlstra To: Andi Kleen Cc: linux-kernel@vger.kernel.org, Andi Kleen , Ingo Molnar , Thomas Gleixner Subject: Re: [PATCH 1/4] x86, perf: Use a new PMU ack sequence on Skylake Message-ID: <20151016115107.GV3816@twins.programming.kicks-ass.net> References: <1444952280-24184-1-git-send-email-andi@firstfloor.org> <1444952280-24184-2-git-send-email-andi@firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1444952280-24184-2-git-send-email-andi@firstfloor.org> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 15, 2015 at 04:37:57PM -0700, Andi Kleen wrote: > One side effect is that the old retry loop is not possible anymore, > as the counters stay unacked for the majority of the PMI handler, > but that is not a big loss, as "profiling" the PMI was always > a bit dubious. For the old ack sequence it is still supported. Its not a self profiling thing, its a safety feature. The interrupt very explicitly disables all PMU counters, which would make self profiling impossible. And note that the "perfevents: irq loop stuck!" WARN is still triggerable on my IVB (although I've not managed to find the root cause of that). What would happen with a 'stuck' event in the new scheme? > In principle the sequence should work on other CPUs too, but > since I only tested on Skylake it is only enabled there. I would very much like a reduction of the ack states. You introduced the late thing, which should also work for everyone, and now you introduce yet another variant. I would very much prefer a single ack scheme if at all possible.