Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161023AbVKXGup (ORCPT ); Thu, 24 Nov 2005 01:50:45 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161022AbVKXGup (ORCPT ); Thu, 24 Nov 2005 01:50:45 -0500 Received: from mx2.suse.de ([195.135.220.15]:37582 "EHLO mx2.suse.de") by vger.kernel.org with ESMTP id S1161019AbVKXGuo (ORCPT ); Thu, 24 Nov 2005 01:50:44 -0500 Date: Thu, 24 Nov 2005 07:50:37 +0100 From: Andi Kleen To: Benjamin LaHaise Cc: Andi Kleen , Jeff Garzik , Andrew Grover , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, john.ronciak@intel.com, christopher.leech@intel.com Subject: Re: [RFC] [PATCH 0/3] ioat: DMA engine support Message-ID: <20051124065037.GZ20775@brahms.suse.de> References: <4384E7F2.2030508@pobox.com> <20051123223007.GA5921@wotan.suse.de> <20051124001700.GC14246@kvack.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20051124001700.GC14246@kvack.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1611 Lines: 38 On Wed, Nov 23, 2005 at 07:17:01PM -0500, Benjamin LaHaise wrote: > On Wed, Nov 23, 2005 at 11:30:08PM +0100, Andi Kleen wrote: > > The main problem I see is that it'll likely only pay off when you can keep > > the queue of copies long (to amortize the cost of > > talking to an external chip). At least for the standard recvmsg > > skb->user space, user space-> skb cases these queues are > > likely short in most cases. That's because most applications > > do relatively small recvmsg or sendmsgs. > > Don't forget that there are benefits of not polluting the cache with the > traffic for the incoming skbs. Is that a general benefit outside benchmarks? I would expect most real programs to actually do something with the data - and that usually involves needing it in cache. > > But it's not clear it's a good idea: a lot of these applications prefer to > > have the target in cache. And IOAT will force it out of cache. > > In the I/O AT case it might make sense to do a few prefetch()es of the > userland data on the return-to-userspace code path. Some prefetches for user space might be a good idea yes > Similarly, we should > make sure that network drivers prefetch the header at the earliest possible > time, too. It's done kind of already but tricky to get right because the prefetch distances upto use are not really long enough -Andi - 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/