From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753577AbaEUWZo (ORCPT ); Wed, 21 May 2014 18:25:44 -0400 Received: from one.firstfloor.org ([193.170.194.197]:58429 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753247AbaEUWZn (ORCPT ); Wed, 21 May 2014 18:25:43 -0400 Date: Thu, 22 May 2014 00:25:41 +0200 From: Andi Kleen To: Andy Lutomirski Cc: Steven Rostedt , "linux-kernel@vger.kernel.org" , "H. Peter Anvin" , Linus Torvalds , Ingo Molnar , Thomas Gleixner , Borislav Petkov , Andi Kleen Subject: Re: [RFC] x86_64: A real proposal for iret-less return to kernel Message-ID: <20140521222541.GO1873@two.firstfloor.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Seems like a lot of effort and risk to essentially only optimize in kernel interrupt handlers. AFAIK the most interesting cases (like user page faults) are not affected at all. Usually most workloads don't spend all that much time in the kernel, so it won't help most interrupts. I suspect the only case that's really interesting here is interrupting idle. Maybe it would be possible to do some fast path in this case only. However idle currently has so much overhead that I suspect that there are lower hanging fruit elsewhere. -Andi -- ak@linux.intel.com -- Speaking for myself only.