From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH] dma-debug: Kconfig for PREALLOC_DMA_DEBUG_ENTRIES Date: Mon, 3 Dec 2018 18:33:22 +0100 Message-ID: <20181203173322.GB8282@lst.de> References: <20181130175449.2625-1-cai@gmx.us> <20181201163657.GA19557@lst.de> <53ab96d7-5dc9-e1a9-4cf2-bb8bf80a3acf@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Christoph Hellwig , Robin Murphy , Qian Cai , netdev@vger.kernel.org, linuxarm@huawei.com, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, yisen.zhuang@huawei.com To: John Garry Return-path: Content-Disposition: inline In-Reply-To: <53ab96d7-5dc9-e1a9-4cf2-bb8bf80a3acf@huawei.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Mon, Dec 03, 2018 at 11:56:11AM +0000, John Garry wrote: > On 01/12/2018 16:36, Christoph Hellwig wrote: >> On Fri, Nov 30, 2018 at 07:39:50PM +0000, Robin Murphy wrote: >>> I was assuming the point was to also add something like >>> >>> default 131072 if HNS_ENET >>> >>> so that DMA debug doesn't require too much thought from the user. If they >>> still have to notice the overflow message and empirically figure out a >>> value that does work, rebuilding the kernel each time is far less >>> convenient than simply adding "dma_debug_entries=..." to their kernel >>> command line and rebooting, which they can do today. If they do already >>> know up-front that the default will need overriding and what the >>> appropriate value is, then the command line still seems seems just as >>> convenient. >> >> I'm not so fond of random drivers changing the defaults. My idea >> was rather to have the config option so that the defconfig files for >> the Hisilicon SOCs with this hardware could select a larger number >> without making a total mess of the kernel configuration. >> >> If we really have to we could do different defaults, but I'd still >> much rather do this on a arch/platform basis than specific drivers. > > As I understand, some drivers could even use much more than this (131072), > to such a point where I can't imagine that we would want to set an arch > default to support them. For this HNS_ENET case, it is arm64 specific so it > would be an arch defconfig. But I'm not sure we could always do the right thing for everyone. I think we might be better of trying to just dynamically allocate entries when we run out of them instead of coming up with a perfect number.