From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jeffrey V. Merkey" Subject: Re: e1000 driver 2.6.18 - how to waste processor cycles Date: Thu, 09 Nov 2006 01:46:52 -0700 Message-ID: <4552EAFC.5060400@soleranetworks.com> References: <45524E3A.7080301@soleranetworks.com> <4807377b0611081701i26ee7ce0k1f822dbbe52c2c8@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "Jeff V. Merkey" , Linux kernel , NetDEV list Return-path: Received: from rwcrmhc14.comcast.net ([204.127.192.84]:14552 "EHLO rwcrmhc14.comcast.net") by vger.kernel.org with ESMTP id S1753760AbWKIHhg (ORCPT ); Thu, 9 Nov 2006 02:37:36 -0500 To: Jesse Brandeburg In-Reply-To: <4807377b0611081701i26ee7ce0k1f822dbbe52c2c8@mail.gmail.com> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Jesse Brandeburg wrote: > included netdev... > > On 11/8/06, Jeff V. Merkey wrote: > >> >> Is there a good reason the skb refill routine in e1000_alloc_rx_buffers >> needs to go and touch and remap skb memory >> on already loaded descriptors/ This seems extremely wasteful of >> processor cycles when refilling the ring buffer. >> >> I note that the archtiecture has changed and is recycling buffers from >> the rx_irq routine and when the routine is called >> to refill the ring buffers, a lot of wasteful and needless calls for >> map_skb is occurring. > > > we have to unmap the descriptor (or at least do > pci_dma_sync_single_for_cpu / pci_dma_sync_single_for_device) because > the dma API says we can't be guaranteed the cacheable memory is > consistent until we do one of the afore mentioned pci dma ops. In the case I am referring to, the memory is already mapped with a previous call, which means it may be getting mapped twice. Jeff > > we have to do *something* before we access it. Simplest path is to > unmap it and then recycle/map it. > > If you can show that it is faster to use pci_dma_sync_single_for_cpu > and friends I'd be glad to take a patch. > > Hope this helps, > Jesse > - > 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/ >