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CH0PR12MB5234.namprd12.prod.outlook.com (2603:10b6:610:d1::24) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.6134.19; Wed, 22 Feb 2023 15:14:32 +0000 Received: from BN8PR12MB3587.namprd12.prod.outlook.com ([fe80::2e4f:4041:28be:ba7a]) by BN8PR12MB3587.namprd12.prod.outlook.com ([fe80::2e4f:4041:28be:ba7a%6]) with mapi id 15.20.6134.019; Wed, 22 Feb 2023 15:14:31 +0000 Message-ID: <29ea3705-5634-c204-c1da-d356b6dfbafc@amd.com> Date: Wed, 22 Feb 2023 16:14:25 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH drm-next v2 05/16] drm: manager to keep track of GPUs VA mappings Content-Language: en-US To: Danilo Krummrich Cc: airlied@gmail.com, daniel@ffwll.ch, tzimmermann@suse.de, mripard@kernel.org, corbet@lwn.net, bskeggs@redhat.com, Liam.Howlett@oracle.com, matthew.brost@intel.com, boris.brezillon@collabora.com, alexdeucher@gmail.com, ogabbay@kernel.org, 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 B6x77ZBE aXlt7DBqpWAfP4hatSDebj1qbaskRicmb1JDTvvsaoPvfw3icW4K3PrAWP5+wvtwHvkfu9EHLAyk1onmQxhdkuz1mZ4AdNcRUu/WfCii26hv0TETbnI/rf0L/GdAZoyecS31YSpCjIuW69C7JO/PmKcOPkEUyep1hJi+Zp8+BFJbvYMJ9CYIe0oRpXjruJ/Ab7Tdg3QE+ufsiPMZ6gQHibGmvQLgpv/HCm8uW9VjNBgHrWwe11HUrvZzHyA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Am 22.02.23 um 16:07 schrieb Danilo Krummrich: > On 2/22/23 11:25, Christian König wrote: >> Am 17.02.23 um 14:44 schrieb Danilo Krummrich: > > > >>> +/** >>> + * DOC: Overview >>> + * >>> + * The DRM GPU VA Manager, represented by struct drm_gpuva_manager >>> keeps track >>> + * of a GPU's virtual address (VA) space and manages the >>> corresponding virtual >>> + * mappings represented by &drm_gpuva objects. It also keeps track >>> of the >>> + * mapping's backing &drm_gem_object buffers. >>> + * >>> + * &drm_gem_object buffers maintain a list (and a corresponding >>> list lock) of >>> + * &drm_gpuva objects representing all existent GPU VA mappings >>> using this >>> + * &drm_gem_object as backing buffer. >>> + * >>> + * If the &DRM_GPUVA_MANAGER_REGIONS feature is enabled, a GPU VA >>> mapping can >>> + * only be created within a previously allocated &drm_gpuva_region, >>> which >>> + * represents a reserved portion of the GPU VA space. GPU VA >>> mappings are not >>> + * allowed to span over a &drm_gpuva_region's boundary. >>> + * >>> + * GPU VA regions can also be flagged as sparse, which allows >>> drivers to create >>> + * sparse mappings for a whole GPU VA region in order to support >>> Vulkan >>> + * 'Sparse Resources'. >> >> Well since we have now found that there is absolutely no technical >> reason for having those regions could we please drop them? > > I disagree this was the outcome of our previous discussion. > > In nouveau I still need them to track the separate sparse page tables > and, as you confirmed previously, Nvidia cards are not the only cards > supporting this feature. > > The second reason is that with regions we can avoid merging between > buffers, which saves some effort. However, I agree that this argument > by itself probably doesn't hold too much, since you've pointed out in > a previous mail that: > > > 1) If we merge and decide to only do that inside certain boundaries > then those boundaries needs to be provided and checked against. This > burns quite some CPU cycles > > 2) If we just merge what we can we might have extra page table updates > which cost time and could result in undesired side effects. > > 3) If we don't merge at all we have additional housekeeping for the > mappings and maybe hw restrictions. > > > However, if a driver uses regions to track its separate sparse page > tables anyway it gets 1) for free, which is a nice synergy. > > I totally agree that regions aren't for everyone though. Hence, I made > them an optional feature and by default regions are disabled. In order > to use them drm_gpuva_manager_init() must be called with the > DRM_GPUVA_MANAGER_REGIONS feature flag. > > I really would not want to open code regions or have two GPUVA manager > instances in nouveau to track sparse page tables. That would be really > messy, hence I hope we can agree on this to be an optional feature. I absolutely don't think that this is a good idea then. This separate handling of sparse page tables is completely Nouveau specific. Even when it's optional feature mixing this into the common handling is exactly what I pointed out as not properly separating between hardware specific and hardware agnostic functionality. This is exactly the problem we ran into with TTM as well and I've spend a massive amount of time to clean that up again. Regards, Christian. > >> >> I don't really see a need for them any more. >> >> Regards, >> Christian. >> >