Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261277AbTIJJxR (ORCPT ); Wed, 10 Sep 2003 05:53:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261284AbTIJJxR (ORCPT ); Wed, 10 Sep 2003 05:53:17 -0400 Received: from mail.jlokier.co.uk ([81.29.64.88]:49040 "EHLO mail.jlokier.co.uk") by vger.kernel.org with ESMTP id S261277AbTIJJxM (ORCPT ); Wed, 10 Sep 2003 05:53:12 -0400 Date: Wed, 10 Sep 2003 10:52:55 +0100 From: Jamie Lokier To: Arjan van de Ven Cc: Luca Veraldi , alexander.riesen@synopsys.COM, linux-kernel Subject: Re: Efficient IPC mechanism on Linux Message-ID: <20030910095255.GA21313@mail.jlokier.co.uk> References: <00f201c376f8$231d5e00$beae7450@wssupremo> <20030909175821.GL16080@Synopsys.COM> <001d01c37703$8edc10e0$36af7450@wssupremo> <20030910064508.GA25795@Synopsys.COM> <015601c3777c$8c63b2e0$5aaf7450@wssupremo> <1063185795.5021.4.camel@laptop.fenrus.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1063185795.5021.4.camel@laptop.fenrus.com> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1335 Lines: 39 Arjan van de Ven wrote: > > The overhead implied by a memcpy() is the same, in the oder of magnitude, > > ***whatever*** kernel version you can develop. > > yes a copy of a page is about 3000 to 4000 cycles on an x86 box in the > uncached case. A pagetable operation (like the cpu setting the accessed > or dirty bit) is in that same order I suspect (maybe half this, but not > a lot less). Changing pagetable content is even more because all the > tlb's and internal cpu state will need to be flushed... which is also a > microcode operation for the cpu. And it's deadly in an SMP environment. I have just done a measurement on a 366MHz PII Celeron. The test is quite crude, but these numbers are upper bounds on the timings: mean 813 cycles to: page fault install zero page remove zero page (= read every page from MAP_ANON region and unmap, repeatedly) mean 11561 cycles to: page fault copy zero page install copy remove copy (= write every page from MAP_ANON region and unmap, repeatedly) I think that makes a clear case for avoiding page copies. -- Jamie - 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/