Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759431AbZAVWy7 (ORCPT ); Thu, 22 Jan 2009 17:54:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752768AbZAVWyv (ORCPT ); Thu, 22 Jan 2009 17:54:51 -0500 Received: from smtp-outbound-2.vmware.com ([65.115.85.73]:51668 "EHLO smtp-outbound-2.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752676AbZAVWyu (ORCPT ); Thu, 22 Jan 2009 17:54:50 -0500 Subject: Re: lmbench lat_mmap slowdown with CONFIG_PARAVIRT From: Zachary Amsden To: Jeremy Fitzhardinge Cc: Nick Piggin , Ingo Molnar , Linux Kernel Mailing List , Linus Torvalds , "hpa@zytor.com" , "jeremy@xensource.com" , "chrisw@sous-sol.org" , "rusty@rustcorp.com.au" , Andrew Morton , Xen-devel In-Reply-To: <4978F6C6.3090003@goop.org> References: <20090120110542.GE19505@wotan.suse.de> <20090120112634.GA20858@elte.hu> <20090120140324.GA26424@elte.hu> <49763806.5090009@goop.org> <20090120205653.GA19710@elte.hu> <20090121072718.GN24891@wotan.suse.de> <4977A051.8050203@goop.org> <1232663311.16317.176.camel@bodhitayantram.eng.vmware.com> <4978F6C6.3090003@goop.org> Content-Type: text/plain Date: Thu, 22 Jan 2009 14:55:07 -0800 Message-Id: <1232664907.16317.182.camel@bodhitayantram.eng.vmware.com> Mime-Version: 1.0 X-Mailer: Evolution 2.22.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1194 Lines: 25 On Thu, 2009-01-22 at 14:44 -0800, Jeremy Fitzhardinge wrote: > I did have some patches to do that at one point. If you set pgd_val = > paravirt_nop, then the patching machinery will completely nop out the > call site. The problem is that it depends on the calling convention > using the same regs for the first arg and return - true for 32-bit, but > not 64. We could fix that with identity functions which the patcher > recognizes and can replace with either pure nops or inline appropriate > register moves. What about removing the identity functions entirely. They are useless, really. All that is needed is a patch site filled with nops for Xen to overwrite, just stuffing the value into the proper registers. For 64-bit, it can be a simple mov to satisfy the constraints. > Also, I just posted patches to get rid of all pvops calls when fetching > or setting flags in a pte, which I hope will help. Sounds like it will help. -- 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/