From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from palrel13.hp.com (palrel13.hp.com [156.153.255.238]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "palrel13.hp.com", Issuer "RSA Data Security, Inc." (verified OK)) by ozlabs.org (Postfix) with ESMTP id 9E0E467B5E for ; Thu, 17 Aug 2006 09:20:43 +1000 (EST) Message-ID: <44E3A572.20600@hp.com> Date: Wed, 16 Aug 2006 16:08:34 -0700 From: Rick Jones MIME-Version: 1.0 To: Linas Vepstas Subject: Re: [PATCH 1/2]: powerpc/cell spidernet bottom half References: <44E34825.2020105@garzik.org> <44E38157.4070805@garzik.org> <20060816.134640.115912460.davem@davemloft.net> <200608162324.47235.arnd@arndb.de> <20060816225558.GM20551@austin.ibm.com> In-Reply-To: <20060816225558.GM20551@austin.ibm.com> Content-Type: text/plain; charset=us-ascii; format=flowed Cc: akpm@osdl.org, Arnd Bergmann , jeff@garzik.org, netdev@vger.kernel.org, jklewis@us.ibm.com, linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, Jens.Osterkamp@de.ibm.com, David Miller List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Linas Vepstas wrote: > On Wed, Aug 16, 2006 at 11:24:46PM +0200, Arnd Bergmann wrote: > >>it only >>seems to be hard to make it go fast using any of them. > > > Last round of measurements seemed linear for packet sizes between > 60 and 600 bytes, suggesting that the hardware can handle a > maximum of 120K descriptors/second, independent of packet size. > I don't know why this is. DMA overhead perhaps? If it takes so many micro/nanoseconds to get a DMA going.... That used to be a reason the Tigon2 had such low PPS rates and issues with multiple buffer packets and a 1500 byte MTU - it had rather high DMA setup latency, and then if you put it into a system with highish DMA read/write latency... well that didn't make it any better :) rick jones