From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mugunthan V N Subject: Re: [PATCH 1/1] net: ethernet: davinci_cpdma: Add boundary for rx and tx descriptors Date: Mon, 10 Dec 2012 16:59:04 +0530 Message-ID: <50C5C780.9060606@ti.com> References: <1355125052-28448-1-git-send-email-mugunthanvnm@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit Cc: , , , , To: Christian Riesch Return-path: In-Reply-To: Sender: linux-omap-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 12/10/2012 1:54 PM, Christian Riesch wrote: > Hi again, > > On Mon, Dec 10, 2012 at 8:37 AM, Mugunthan V N wrote: >> When there is heavy transmission traffic in the CPDMA, then Rx descriptors >> memory is also utilized as tx desc memory this leads to reduced rx desc memory >> which leads to poor performance. >> > "poor performance" is an understatement, see Sascha's description of > his patch. At initialization of the driver, half of the descriptors in > the pool are allocated for rx. When a packet arrives, one of the rx > descriptors is released and a new one is allocated. If tx allocates > this descriptor in the meantime, it is lost for rx forever! If tx > consumes all rx descriptors this way, the rx channel is dead! > > Regards, Christian > >> This patch adds boundary for tx and rx descriptors in bd ram dividing the >> descriptor memory to ensure that during heavy transmission tx doesn't use >> rx descriptors. >> >> This patch is already applied to davinci_emac driver, since CPSW and >> davici_dmac uses the same CPDMA, moving the boundry seperation from >> Davinci EMAC driver to CPDMA driver which was done in the following >> commit >> >> commit 86d8c07ff2448eb4e860e50f34ef6ee78e45c40c >> Author: Sascha Hauer >> Date: Tue Jan 3 05:27:47 2012 +0000 >> >> net/davinci: do not use all descriptors for tx packets >> >> The driver uses a shared pool for both rx and tx descriptors. >> During open it queues fixed number of 128 descriptors for receive >> packets. For each received packet it tries to queue another >> descriptor. If this fails the descriptor is lost for rx. >> The driver has no limitation on tx descriptors to use, so it >> can happen during a nmap / ping -f attack that the driver >> allocates all descriptors for tx and looses all rx descriptors. >> The driver stops working then. >> To fix this limit the number of tx descriptors used to half of >> the descriptors available, the rx path uses the other half. >> >> Tested on a custom board using nmap / ping -f to the board from >> two different hosts. >> >> Signed-off-by: Mugunthan V N Will change the commit description and resubmit the patch. Regards Mugunthan V N