From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030766AbWI0U2L (ORCPT ); Wed, 27 Sep 2006 16:28:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030769AbWI0U2L (ORCPT ); Wed, 27 Sep 2006 16:28:11 -0400 Received: from gw.goop.org ([64.81.55.164]:25056 "EHLO mail.goop.org") by vger.kernel.org with ESMTP id S1030767AbWI0U2I (ORCPT ); Wed, 27 Sep 2006 16:28:08 -0400 Message-ID: <451ADEE4.4010508@goop.org> Date: Wed, 27 Sep 2006 13:28:20 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 1.5.0.7 (X11/20060913) MIME-Version: 1.0 To: Pavel Machek CC: Linux Kernel Mailing List , Andrew Morton , Rusty Russell Subject: Re: [PATCH 0/6] Per-processor private data areas for i386 References: <20060925184540.601971833@goop.org> <20060927194600.GA4538@ucw.cz> In-Reply-To: <20060927194600.GA4538@ucw.cz> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Pavel Machek wrote: > So we have 4% slowdown... > Yes, that would be the worst-case slowdown in the hot-cache case. Rearranging the layout of the GDT would remove any theoretical cold-cache slowdown (I haven't measured if there's any impact in practice). > ...and 0.2% smaller kernel. I guess you should demonstrate speedup at > complex syscalls before wedecide it is worth it... That would be nice, but this patch series isn't really intended to be a performance improvement. That would be nice, but the main motivation is to make inline assembler patching for the paravirt work cleaner. Rusty and I have also been investigating how to use the %gs-based memory to implement all percpu data, rather than the few special cases this patch series currently covers, which will help further amortize the entry/exit cost. Rusty has also done more comprehensive benchmarks with his variant of this patch series, and found no statistically interesting performance difference. Which is pretty much what I would expect, since it doesn't increase cache-misses at all. J