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([2a02:908:1252:fb60:9e25:63a7:d115:3eab]) by smtp.gmail.com with ESMTPSA id n186sm2168506wme.31.2021.09.21.02.41.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Sep 2021 02:41:53 -0700 (PDT) Subject: Re: [Intel-gfx] [PATCH 13/26] drm/i915: use the new iterator in i915_gem_busy_ioctl To: Tvrtko Ursulin , linaro-mm-sig@lists.linaro.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, intel-gfx@lists.freedesktop.org Cc: daniel@ffwll.ch References: <20210917123513.1106-1-christian.koenig@amd.com> <20210917123513.1106-14-christian.koenig@amd.com> <6fbaca09-ec51-c44e-708c-334ef8be8595@linux.intel.com> <368e8495-f4de-cbb2-3584-e022a5937885@gmail.com> <563bb7c3-f956-212d-6085-b1b88292887c@linux.intel.com> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: <64b6a924-be38-0ed0-da92-86296702f71c@gmail.com> Date: Tue, 21 Sep 2021 11:41:52 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <563bb7c3-f956-212d-6085-b1b88292887c@linux.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Am 20.09.21 um 12:33 schrieb Tvrtko Ursulin: > On 20/09/2021 11:13, Christian König wrote: >> Am 20.09.21 um 10:45 schrieb Tvrtko Ursulin: >>> >>> On 17/09/2021 13:35, Christian König wrote: >>>> This makes the function much simpler since the complex >>>> retry logic is now handled else where. >>>> >>>> Signed-off-by: Christian König >>>> --- >>>>   drivers/gpu/drm/i915/gem/i915_gem_busy.c | 32 >>>> ++++++++---------------- >>>>   1 file changed, 11 insertions(+), 21 deletions(-) >>>> >>>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_busy.c >>>> b/drivers/gpu/drm/i915/gem/i915_gem_busy.c >>>> index 6234e17259c1..b1cb7ba688da 100644 >>>> --- a/drivers/gpu/drm/i915/gem/i915_gem_busy.c >>>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_busy.c >>>> @@ -82,8 +82,8 @@ i915_gem_busy_ioctl(struct drm_device *dev, void >>>> *data, >>>>   { >>>>       struct drm_i915_gem_busy *args = data; >>>>       struct drm_i915_gem_object *obj; >>>> -    struct dma_resv_list *list; >>>> -    unsigned int seq; >>>> +    struct dma_resv_iter cursor; >>>> +    struct dma_fence *fence; >>>>       int err; >>>>         err = -ENOENT; >>>> @@ -109,27 +109,17 @@ i915_gem_busy_ioctl(struct drm_device *dev, >>>> void *data, >>>>        * to report the overall busyness. This is what the >>>> wait-ioctl does. >>>>        * >>>>        */ >>>> -retry: >>>> -    seq = raw_read_seqcount(&obj->base.resv->seq); >>>> - >>>> -    /* Translate the exclusive fence to the READ *and* WRITE >>>> engine */ >>>> -    args->busy = >>>> busy_check_writer(dma_resv_excl_fence(obj->base.resv)); >>>> - >>>> -    /* Translate shared fences to READ set of engines */ >>>> -    list = dma_resv_shared_list(obj->base.resv); >>>> -    if (list) { >>>> -        unsigned int shared_count = list->shared_count, i; >>>> - >>>> -        for (i = 0; i < shared_count; ++i) { >>>> -            struct dma_fence *fence = >>>> -                rcu_dereference(list->shared[i]); >>>> - >>>> +    args->busy = false; >>>> +    dma_resv_iter_begin(&cursor, obj->base.resv, true); >>>> +    dma_resv_for_each_fence_unlocked(&cursor, fence) { >>> >>> You did not agree with my suggestion to reset args->busy on restart >>> and so preserve current behaviour? >> >> No, I want to keep the restart behavior internally to the dma_resv >> object and as far as I can see it should not make a difference here. > > To be clear, on paper difference between old and new implementation is > if the restart happens while processing the shared fences. > > Old implementation unconditionally goes to "args->busy = > >>> busy_check_writer(dma_resv_excl_fence(obj->base.resv));" and so > overwrites the set of flags returned to userspace. > > New implementation can merge new read flags to the old set of flags > and so return a composition of past and current fences. > > Maybe it does not matter hugely in this case, depends if userspace > typically just restarts until flags are clear. But I am not sure. > > On the higher level - what do you mean with wanting to keep the > restart behaviour internal? Not providing iterators users means of > detecting it? I think it has to be provided. Ok I will adjust that for now to get the patch set upstream. But in general when somebody outside of the dma_resv code base depends on the restart behavior then that's a bug inside the design of that code. The callers should only care about what unsignaled fences are inside the dma_resv container and it shouldn't matter if those fences are presented once or multiple times because of a reset.. When this makes a difference we have a bug in the handling and should probably consider taking the dma_resv.lock instead. Regards, Christian. > > Regards, > > Tvrtko > >> Regards, >> Christian. >> >>> >>> Regards, >>> >>> Tvrtko >>> >>>> +        if (dma_resv_iter_is_exclusive(&cursor)) >>>> +            /* Translate the exclusive fence to the READ *and* >>>> WRITE engine */ >>>> +            args->busy = busy_check_writer(fence); >>>> +        else >>>> +            /* Translate shared fences to READ set of engines */ >>>>               args->busy |= busy_check_reader(fence); >>>> -        } >>>>       } >>>> - >>>> -    if (args->busy && read_seqcount_retry(&obj->base.resv->seq, seq)) >>>> -        goto retry; >>>> +    dma_resv_iter_end(&cursor); >>>>         err = 0; >>>>   out: >>>> >>