Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751805Ab3CWRLr (ORCPT ); Sat, 23 Mar 2013 13:11:47 -0400 Received: from mail-vc0-f171.google.com ([209.85.220.171]:60136 "EHLO mail-vc0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751622Ab3CWRLq (ORCPT ); Sat, 23 Mar 2013 13:11:46 -0400 MIME-Version: 1.0 In-Reply-To: <1364001923-10796-1-git-send-email-andi@firstfloor.org> References: <1364001923-10796-1-git-send-email-andi@firstfloor.org> Date: Sat, 23 Mar 2013 10:11:45 -0700 X-Google-Sender-Auth: 4zDkcSS9WlvhthqeUYXKvhaSCx4 Message-ID: Subject: Re: RFC: Kernel lock elision for TSX From: Linus Torvalds To: Andi Kleen Cc: Linux Kernel Mailing List , Andrew Morton , "the arch/x86 maintainers" , Benjamin Herrenschmidt Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1657 Lines: 40 On Fri, Mar 22, 2013 at 6:24 PM, Andi Kleen wrote: > > Some questions and answers: > > - How much does it improve performance? > I cannot share any performance numbers at this point unfortunately. > Also please keep in mind that the tuning is very preliminary and > will be revised. Quite frankly, since the *only* reason for RTM is performance, this fundamentally makes the patch-set pointless. If we don't know how much it helps, we can't judge whether it's worth even discussing this patch. It adds enough complexity that it had better be worth it, and without knowing the performance side, all we can see are the negatives. Talk to your managers about this. Tell them that without performance numbers, any patch-series like this is totally pointless. Does it make non-contended code slower? We don't know. Does it improve anything but micro-benchmarks? We don't know. Is there any point to this? WE DON"T KNOW. Inside of intel, it might be useful for testing and validating the hardware. Outside of intel, it is totally useless without performance numbers. The other comment I have is that since it does touch non-x86 header files etc (although not a lot), you really need to talk to the POWER8 people about naming of the thing. Calling it and having "generic" helpers called _xtest() used by the generic spinlock code sounds a bit suspect. Linus -- 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/