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([2a02:810d:4b3f:de9c:642:1aff:fe31:a15c]) by smtp.gmail.com with ESMTPSA id l5-20020a170902d34500b001b5640a8874sm5438809plk.293.2023.06.22.07.22.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 22 Jun 2023 07:22:48 -0700 (PDT) Message-ID: Date: Thu, 22 Jun 2023 16:22:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [PATCH drm-next v5 03/14] drm: manager to keep track of GPUs VA mappings Content-Language: en-US To: =?UTF-8?Q?Christian_K=c3=b6nig?= , 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, bagasdotme@gmail.com, willy@infradead.org, jason@jlekstrand.net Cc: dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Donald Robson , Dave Airlie References: <20230620004217.4700-1-dakr@redhat.com> <20230620004217.4700-4-dakr@redhat.com> <41aecd10-9956-0752-2838-34c97834f0c8@amd.com> From: Danilo Krummrich Organization: RedHat In-Reply-To: <41aecd10-9956-0752-2838-34c97834f0c8@amd.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/22/23 15:54, Christian König wrote: > Am 20.06.23 um 14:23 schrieb Danilo Krummrich: >> Hi Christian, >> >> On 6/20/23 08:45, Christian König wrote: >>> Hi Danilo, >>> >>> sorry for the delayed reply. I've trying to dig myself out of a hole >>> at the moment. >> >> No worries, thank you for taking a look anyway! >> >>> >>> Am 20.06.23 um 02:42 schrieb Danilo Krummrich: >>>> [SNIP] >>>> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h >>>> index bbc721870c13..5ec8148a30ee 100644 >>>> --- a/include/drm/drm_gem.h >>>> +++ b/include/drm/drm_gem.h >>>> @@ -36,6 +36,8 @@ >>>>   #include >>>>   #include >>>> +#include >>>> +#include >>>>   #include >>>> @@ -379,6 +381,18 @@ struct drm_gem_object { >>>>        */ >>>>       struct dma_resv _resv; >>>> +    /** >>>> +     * @gpuva: >>>> +     * >>>> +     * Provides the list of GPU VAs attached to this GEM object. >>>> +     * >>>> +     * Drivers should lock list accesses with the GEMs &dma_resv lock >>>> +     * (&drm_gem_object.resv). >>>> +     */ >>>> +    struct { >>>> +        struct list_head list; >>>> +    } gpuva; >>>> + >>>>       /** >>>>        * @funcs: >>>>        * >>> >>> I'm pretty sure that it's not a good idea to attach this directly to >>> the GEM object. >> >> Why do you think so? IMHO having a common way to connect mappings to >> their backing buffers is a good thing, since every driver needs this >> connection anyway. >> >> E.g. when a BO gets evicted, drivers can just iterate the list of >> mappings and, as the circumstances require, invalidate the >> corresponding mappings or to unmap all existing mappings of a given >> buffer. >> >> What would be the advantage to let every driver implement a driver >> specific way of keeping this connection? > > Flexibility. For example on amdgpu the mappings of a BO are groups by VM > address spaces. > > E.g. the BO points to multiple bo_vm structures which in turn have lists > of their mappings. Isn't this (almost) the same relationship I introduce with the GPUVA manager? If you would switch over to the GPUVA manager right now, it would be that every GEM has a list of it's mappings (the gpuva list). The mapping is represented by struct drm_gpuva (of course embedded in driver specific structure(s)) which has a pointer to the VM address space it is part of, namely the GPUVA manager instance. And the GPUVA manager keeps a maple tree of it's mappings as well. If you still would like to *directly* (indirectly you already have that relationship) keep a list of GPUVA managers (VM address spaces) per GEM, you could still do that in a driver specific way. Do I miss something? > > Additional to that there is a state maschine associated with the > mappings, e.g. if the page tables are up to date or need to be updated > etc.... > >> Do you see cases where this kind of connection between mappings and >> backing buffers wouldn't be good enough? If so, which cases do you >> have in mind? Maybe we can cover them in a common way as well? > > Yeah, we have tons of cases like that. But I have no idea how to > generalize them. They could still remain to be driver specific then, right? > >> >>> >>> As you wrote in the commit message it's highly driver specific what >>> to map and where to map it. >> >> In the end the common case should be that in a VA space at least every >> mapping being backed by a BO is represented by a struct drm_gpuva. > > Oh, no! We also have mappings not backed by a BO at all! For example for > partial resident textures or data routing to internal hw etc... > > You can't be sure that a mapping is backed by a BO at all. I fully agree, that's why I wrote "the common case should be that in a VA space at least every mapping *being backed by a BO* is represented by a struct drm_gpuva". Mappings not being backed by an actual BO would not be linked to a GEM of course. > >> >>> >>> Instead I suggest to have a separate structure for mappings in a VA >>> space which driver can then add to their GEM objects or whatever they >>> want to map into their VMs. >> >> Which kind of separate structure for mappings? Another one analogous >> to struct drm_gpuva? > > Well similar to what amdgpu uses BO -> one structure for each > combination of BO and VM -> mappings inside that VM As explained above, I think that's exactly what the GPUVA manager does, just in another order: BO has list of mappings, mappings have pointer to VM, VM has list (or actually a maple tree) of mappings. You see any advantages or disadvantages of either order of relationships? For me it looks like it doesn't really matter which one to pick. - Danilo > > Regards, > Christian. > >> >> - Danilo >> >>> >>> Regards, >>> Christian. >>> >>> >> >