Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932162AbbDQNMw (ORCPT ); Fri, 17 Apr 2015 09:12:52 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:44574 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753458AbbDQNMv (ORCPT ); Fri, 17 Apr 2015 09:12:51 -0400 Date: Fri, 17 Apr 2015 15:12:37 +0200 From: Peter Zijlstra To: "Liang, Kan" Cc: "linux-kernel@vger.kernel.org" , "mingo@kernel.org" , "acme@infradead.org" , "eranian@google.com" , "andi@firstfloor.org" Subject: Re: [PATCH V6 4/6] perf, x86: handle multiple records in PEBS buffer Message-ID: <20150417131237.GH23123@twins.programming.kicks-ass.net> References: <1428597466-8154-1-git-send-email-kan.liang@intel.com> <1428597466-8154-5-git-send-email-kan.liang@intel.com> <20150416125342.GZ23123@twins.programming.kicks-ass.net> <20150417081100.GZ24151@twins.programming.kicks-ass.net> <37D7C6CF3E00A74B8858931C1DB2F077017CB364@SHSMSX103.ccr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <37D7C6CF3E00A74B8858931C1DB2F077017CB364@SHSMSX103.ccr.corp.intel.com> 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 Content-Length: 1351 Lines: 36 On Fri, Apr 17, 2015 at 12:50:33PM +0000, Liang, Kan wrote: > > > > > > > > A) the CTRn value reaches 0: > > > - the corresponding bit in GLOBAL_STATUS gets set > > > - we start arming the hardware assist > > > > > > < some unspecified amount of time later -- > > > this could cover multiple events of interest > > > > > > > B) the hardware assist is armed, any next event will trigger it > > > > > > C) a matching event happens: > > > - the hardware assist triggers and generates a PEBS record > > > this includes a copy of GLOBAL_STATUS at this moment > > > - if we auto-reload we (re)set CTRn > > > > Is this actually true? Do we reload here or on A ? > > > > Yes, on C. > According to SDM Volume 3, 18.7.1.1, the reset value will be > loaded after each PEBS record is written, which is done > by hw assist. OK, then I did indeed remember that right. But that brings us to patch 1 of this series, how is that correct in the face of this? There is an arbitrary delay (A->B) added to the period. And the Changelog of course never did bother to make that clear. -- 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/