From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753405AbcFBQEe (ORCPT ); Thu, 2 Jun 2016 12:04:34 -0400 Received: from mga02.intel.com ([134.134.136.20]:44727 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751455AbcFBQEd (ORCPT ); Thu, 2 Jun 2016 12:04:33 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,406,1459839600"; d="scan'208";a="993924895" Date: Thu, 2 Jun 2016 09:04:28 -0700 From: Andi Kleen To: David Carrillo-Cisneros Cc: linux-kernel@vger.kernel.org, "x86@kernel.org" , Ingo Molnar , "Yan, Zheng" , Kan Liang , Peter Zijlstra , Stephane Eranian Subject: Re: [PATCH 1/3] perf/x86/intel: output LBR support statement after validation Message-ID: <20160602160428.GR22049@tassilo.jf.intel.com> References: <1464835323-33872-1-git-send-email-davidcc@google.com> <1464835323-33872-2-git-send-email-davidcc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1464835323-33872-2-git-send-email-davidcc@google.com> User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I don't think the context switch support is really needed. It's only needed for saving/restoring LBRs, and we only do that with LBR callstacks. In any other LBR mode that LBRs are only flushed on context switch But LBR callstacks will never put kernel addresses into the LBRs because they are forced to set a ring 3 filter. So you can't have kernel addresses in the LBR when saving/restoring them (unless I missed some case) Dropping that will likely simplify the patch somewhat. -Andi