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

[Christian König <christian.koenig@xxxxxxx>]

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@xxxxxxx>
> > > Cc: "Thomas Hellström" <thomas.hellstrom@xxxxxxxxxxxxxxx>
> > > Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
> > > Signed-off-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>
> > > ---
> > >   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);
> > >           }