[Intel-gfx] [PATCH v4 20/61] drm/i915: Rework clflush to work correctly without obj->mm.lock.

[Thomas Hellström]

On 11/2/20 9:48 AM, Maarten Lankhorst wrote:
> Op 30-10-2020 om 16:08 schreef Thomas Hellström:
>> On 10/16/20 12:44 PM, Maarten Lankhorst wrote:
>>> Pin in the caller, not in the work itself. This should also
>>> work better for dma-fence annotations.
>>>
>>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>>> ---
>>>    drivers/gpu/drm/i915/gem/i915_gem_clflush.c | 15 +++++++--------
>>>    1 file changed, 7 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_clflush.c b/drivers/gpu/drm/i915/gem/i915_gem_clflush.c
>>> index bc0223716906..daf9284ef1f5 100644
>>> --- a/drivers/gpu/drm/i915/gem/i915_gem_clflush.c
>>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_clflush.c
>>> @@ -27,15 +27,8 @@ static void __do_clflush(struct drm_i915_gem_object *obj)
>>>    static int clflush_work(struct dma_fence_work *base)
>>>    {
>>>        struct clflush *clflush = container_of(base, typeof(*clflush), base);
>>> -    struct drm_i915_gem_object *obj = clflush->obj;
>>> -    int err;
>>>    -    err = i915_gem_object_pin_pages(obj);
>>> -    if (err)
>>> -        return err;
>>> -
>>> -    __do_clflush(obj);
>>> -    i915_gem_object_unpin_pages(obj);
>>> +    __do_clflush(clflush->obj);
>>>          return 0;
>>>    }
>>> @@ -44,6 +37,7 @@ static void clflush_release(struct dma_fence_work *base)
>>>    {
>>>        struct clflush *clflush = container_of(base, typeof(*clflush), base);
>>>    +    i915_gem_object_unpin_pages(clflush->obj);
>> Hmm, Could we do without pinning here? Pages present are protected first by the object lock, then by the fence?
>>
>> /Thomas
>>
>>
>>
> I felt the least chance of regressions was to copy the existing code. :)
>
> At least until we have completed obj->mm.lock removal, we shouldn't try to be smart with these kind of things.
>
> Likely, we've already pinned the pages, so it's a simple ref increase.
>
> Later on, we can try to be smart, but whenever I tried to change behavior so far, I was forced to hunt down bugs.

OK, sounds good.

/Thomas



>
> ~Maarten
>