[PATCH] drm/ttm/pool: Revert to clear-on-alloc to honor TTM_TT_FLAG_ZERO_ALLOC

[Christian König]

Am 21.06.24 um 17:43 schrieb Nirmoy Das:
> Hi Christian,
>
> On 6/21/2024 4:54 PM, Christian König wrote:
>> Am 20.06.24 um 18:01 schrieb Nirmoy Das:
>>> Currently ttm pool is not honoring TTM_TT_FLAG_ZERO_ALLOC flag and
>>> clearing pages on free. It does help with allocation latency but 
>>> clearing
>>> happens even if drm driver doesn't passes the flag. If clear on free
>>> is needed then a new flag can be added for that purpose.
>>
>> Mhm, thinking more about it that will most likely get push back from 
>> others as well.
>
>
> Agreed, it is diverting a lot from a known behavior.
>
>>
>> How about the attached patch? We just skip clearing pages when the 
>> driver set the ZERO_ALLOC flag again before freeing them.
>>
>> Maybe rename the flag or add a new one for that, but in general that 
>> looks like the option with the least impact.
>
>
> I would prefer a few flag (TTM_TT_FLAG_CLEARED_ALLOC ?) which driver 
> can set before freeing. I can resend the patch if you are
>
> fine with it.


Yeah, please go ahead with that. But probably better name it 
TTM_TT_FLAG_CLEARED_ON_FREE.

Thanks,
Christian.

>
>
> Regards,
>
> Nirmoy
>
>
>>
>> Regards,
>> Christian.
>>
>>>
>>> Cc: Christian Koenig <christian.koenig at amd.com>
>>> Cc: "Thomas Hellström" <thomas.hellstrom at linux.intel.com>
>>> Cc: Matthew Auld <matthew.auld at intel.com>
>>> Signed-off-by: Nirmoy Das <nirmoy.das at intel.com>
>>> ---
>>>   drivers/gpu/drm/ttm/ttm_pool.c | 31 +++++++++++++++++--------------
>>>   1 file changed, 17 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/ttm/ttm_pool.c 
>>> b/drivers/gpu/drm/ttm/ttm_pool.c
>>> index 6e1fd6985ffc..cbbd722185ee 100644
>>> --- a/drivers/gpu/drm/ttm/ttm_pool.c
>>> +++ b/drivers/gpu/drm/ttm/ttm_pool.c
>>> @@ -224,15 +224,6 @@ static void ttm_pool_unmap(struct ttm_pool 
>>> *pool, dma_addr_t dma_addr,
>>>   /* Give pages into a specific pool_type */
>>>   static void ttm_pool_type_give(struct ttm_pool_type *pt, struct 
>>> page *p)
>>>   {
>>> -    unsigned int i, num_pages = 1 << pt->order;
>>> -
>>> -    for (i = 0; i < num_pages; ++i) {
>>> -        if (PageHighMem(p))
>>> -            clear_highpage(p + i);
>>> -        else
>>> -            clear_page(page_address(p + i));
>>> -    }
>>> -
>>>       spin_lock(&pt->lock);
>>>       list_add(&p->lru, &pt->pages);
>>>       spin_unlock(&pt->lock);
>>> @@ -240,15 +231,26 @@ static void ttm_pool_type_give(struct 
>>> ttm_pool_type *pt, struct page *p)
>>>   }
>>>     /* Take pages from a specific pool_type, return NULL when 
>>> nothing available */
>>> -static struct page *ttm_pool_type_take(struct ttm_pool_type *pt)
>>> +static struct page *ttm_pool_type_take(struct ttm_pool_type *pt, 
>>> bool clear)
>>>   {
>>>       struct page *p;
>>>         spin_lock(&pt->lock);
>>>       p = list_first_entry_or_null(&pt->pages, typeof(*p), lru);
>>>       if (p) {
>>> +        unsigned int i, num_pages = 1 << pt->order;
>>> +
>>>           atomic_long_sub(1 << pt->order, &allocated_pages);
>>>           list_del(&p->lru);
>>> +        if (clear) {
>>> +            for (i = 0; i < num_pages; ++i) {
>>> +                if (PageHighMem(p))
>>> +                    clear_highpage(p + i);
>>> +                else
>>> +                    clear_page(page_address(p + i));
>>> +            }
>>> +        }
>>> +
>>>       }
>>>       spin_unlock(&pt->lock);
>>>   @@ -279,7 +281,7 @@ static void ttm_pool_type_fini(struct 
>>> ttm_pool_type *pt)
>>>       list_del(&pt->shrinker_list);
>>>       spin_unlock(&shrinker_lock);
>>>   -    while ((p = ttm_pool_type_take(pt)))
>>> +    while ((p = ttm_pool_type_take(pt, false)))
>>>           ttm_pool_free_page(pt->pool, pt->caching, pt->order, p);
>>>   }
>>>   @@ -330,7 +332,7 @@ static unsigned int ttm_pool_shrink(void)
>>>       list_move_tail(&pt->shrinker_list, &shrinker_list);
>>>       spin_unlock(&shrinker_lock);
>>>   -    p = ttm_pool_type_take(pt);
>>> +    p = ttm_pool_type_take(pt, false);
>>>       if (p) {
>>>           ttm_pool_free_page(pt->pool, pt->caching, pt->order, p);
>>>           num_pages = 1 << pt->order;
>>> @@ -457,10 +459,11 @@ int ttm_pool_alloc(struct ttm_pool *pool, 
>>> struct ttm_tt *tt,
>>>            num_pages;
>>>            order = min_t(unsigned int, order, __fls(num_pages))) {
>>>           struct ttm_pool_type *pt;
>>> +        bool clear = tt->page_flags & TTM_TT_FLAG_ZERO_ALLOC;
>>>             page_caching = tt->caching;
>>>           pt = ttm_pool_select_type(pool, tt->caching, order);
>>> -        p = pt ? ttm_pool_type_take(pt) : NULL;
>>> +        p = pt ? ttm_pool_type_take(pt, clear) : NULL;
>>>           if (p) {
>>>               r = ttm_pool_apply_caching(caching, pages,
>>>                              tt->caching);
>>> @@ -480,7 +483,7 @@ int ttm_pool_alloc(struct ttm_pool *pool, struct 
>>> ttm_tt *tt,
>>>                   if (num_pages < (1 << order))
>>>                       break;
>>>   -                p = ttm_pool_type_take(pt);
>>> +                p = ttm_pool_type_take(pt, clear);
>>>               } while (p);
>>>           }