From mboxrd@z Thu Jan 1 00:00:00 1970 From: w@1wt.eu (Willy Tarreau) Date: Thu, 21 Nov 2013 23:13:10 +0100 Subject: ARM network performance and dma_mask In-Reply-To: <528E82C6.2010106@gmail.com> References: <20131119174323.GH913@1wt.eu> <1384885910.8604.110.camel@edumazet-glaptop2.roam.corp.google.com> <20131119184121.GN913@1wt.eu> <874n780wzc.fsf@natisbad.org> <20131120191145.GP8581@1wt.eu> <87txf692zx.fsf@natisbad.org> <20131120215435.GT8581@1wt.eu> <20131121004430.GX8581@1wt.eu> <20131121183834.GB18513@1wt.eu> <528E82C6.2010106@gmail.com> Message-ID: <20131121221310.GG18513@1wt.eu> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Nov 21, 2013 at 04:01:42PM -0600, Rob Herring wrote: > The patch was to fix this issue[1]. It is fixed in the core code because > dma_mask not being set has been a known issue with DT probing for some > time. Since most drivers don't seem to care, we've gotten away with it. > I thought the normal failure mode was drivers failing to probe. It seems that very few drivers try to set their mask, so probably that the default value was already OK even though less performant. > As to why it helps performance, I'm not really sure. Perhaps it is > causing some bounce buffers to be used. That's also the thing I have been thinking about, and given this device only has a 16-bit DDR bus, bounce buffers can make a difference. > Rob > > [1] http://lists.xen.org/archives/html/xen-devel/2013-10/msg00092.html Thanks for your quick explanation Rob! Willy From mboxrd@z Thu Jan 1 00:00:00 1970 From: Willy Tarreau Subject: Re: ARM network performance and dma_mask Date: Thu, 21 Nov 2013 23:13:10 +0100 Message-ID: <20131121221310.GG18513@1wt.eu> References: <20131119174323.GH913@1wt.eu> <1384885910.8604.110.camel@edumazet-glaptop2.roam.corp.google.com> <20131119184121.GN913@1wt.eu> <874n780wzc.fsf@natisbad.org> <20131120191145.GP8581@1wt.eu> <87txf692zx.fsf@natisbad.org> <20131120215435.GT8581@1wt.eu> <20131121004430.GX8581@1wt.eu> <20131121183834.GB18513@1wt.eu> <528E82C6.2010106@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Arnaud Ebalard , Thomas Petazzoni , Florian Fainelli , simon.guinot@sequanux.org, Eric Dumazet , netdev@vger.kernel.org, edumazet@google.com, Cong Wang , linux-arm-kernel@lists.infradead.org To: Rob Herring Return-path: Received: from 1wt.eu ([62.212.114.60]:51054 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755201Ab3KUWNi (ORCPT ); Thu, 21 Nov 2013 17:13:38 -0500 Content-Disposition: inline In-Reply-To: <528E82C6.2010106@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, Nov 21, 2013 at 04:01:42PM -0600, Rob Herring wrote: > The patch was to fix this issue[1]. It is fixed in the core code because > dma_mask not being set has been a known issue with DT probing for some > time. Since most drivers don't seem to care, we've gotten away with it. > I thought the normal failure mode was drivers failing to probe. It seems that very few drivers try to set their mask, so probably that the default value was already OK even though less performant. > As to why it helps performance, I'm not really sure. Perhaps it is > causing some bounce buffers to be used. That's also the thing I have been thinking about, and given this device only has a 16-bit DDR bus, bounce buffers can make a difference. > Rob > > [1] http://lists.xen.org/archives/html/xen-devel/2013-10/msg00092.html Thanks for your quick explanation Rob! Willy