[PATCH 5/6] drm/ttm: replace dma_resv object on deleted BOs v2

[Christian König]

Am 11.02.20 um 16:02 schrieb Pan, Xinhui:
>
>> 2020年2月11日 22:14，Daniel Vetter <daniel at ffwll.ch> 写道：
>>
>> On Mon, Feb 10, 2020 at 04:09:06PM +0100, Christian König wrote:
>>> When non-imported BOs are resurrected for delayed delete we replace
>>> the dma_resv object to allow for easy reclaiming of the resources.
>>>
>>> v2: move that to ttm_bo_individualize_resv
>>>
>>> Signed-off-by: Christian König <christian.koenig at amd.com>
>>> ---
>>> drivers/gpu/drm/ttm/ttm_bo.c | 10 +++++++++-
>>> 1 file changed, 9 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
>>> index d0624685f5d2..4d161038de98 100644
>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
>>> @@ -393,6 +393,14 @@ static int ttm_bo_individualize_resv(struct ttm_buffer_object *bo)
>>>
>>> 	r = dma_resv_copy_fences(&bo->base._resv, bo->base.resv);
>>> 	dma_resv_unlock(&bo->base._resv);
>>> +	if (r)
>>> +		return r;
>>> +
>>> +	if (bo->type != ttm_bo_type_sg) {
>>> +		spin_lock(&ttm_bo_glob.lru_lock);
>>> +		bo->base.resv = &bo->base._resv;
>> Having the dma_resv pointer be protected by the lru_lock for ttm internal
>> stuff, but invariant everywhere else is really confusing. Not sure that's
> I think this is reader VS writer.
> To avoid any internal functions using the old resv,  using an existing spin lock is acceptable.
> Maybe RCU is better? That will need a lot of effort.
> Anyway, ttm sucks. We HAS done a lot of work on it to make it better running on modern system.

Yeah that summarize my recent presentation about TTM pretty much :)

Double checked that and the only reason we have the lock is that in 
ttm_mem_evict_first() we trylock first and then grab a reference.

So we should probably rework that code as well and then we can also drop 
that lock here, but that should come later.

Christian.

>
>
>> a great idea, I've just chased some ttm code around freaking out about
>> that.
>> -Daniel
>>
>>> +		spin_unlock(&ttm_bo_glob.lru_lock);
>>> +	}
>>>
>>> 	return r;
>>> }
>>> @@ -720,7 +728,7 @@ static bool ttm_bo_evict_swapout_allowable(struct ttm_buffer_object *bo,
>>>
>>> 	if (bo->base.resv == ctx->resv) {
>>> 		dma_resv_assert_held(bo->base.resv);
>>> -		if (ctx->flags & TTM_OPT_FLAG_ALLOW_RES_EVICT || bo->deleted)
>>> +		if (ctx->flags & TTM_OPT_FLAG_ALLOW_RES_EVICT)
>>> 			ret = true;
>>> 		*locked = false;
>>> 		if (busy)
>>> -- 
>>> 2.17.1
>>>
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>> -- 
>> Daniel Vetter
>> Software Engineer, Intel Corporation
>> https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fblog.ffwll.ch&data=02%7C01%7CXinhui.Pan%40amd.com%7Cee67310e26b64ca9e79008d7aefca7b4%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637170272481765904&sdata=fk28jtHhAnE312CFMgVXaZtaS2YNqJjmyJ317FWjAoM%3D&reserved=0