[RFC PATCH 07/16] drm/ttm: Reduce the number of used allocation orders for TTM pages
Christian König
christian.koenig at amd.com
Wed Feb 15 18:30:35 UTC 2023
Am 15.02.23 um 19:12 schrieb Thomas Hellström:
> On Wed, 2023-02-15 at 18:42 +0100, Christian König wrote:
>> Am 15.02.23 um 17:13 schrieb Thomas Hellström:
>>> When swapping out, we will split multi-order pages both in order to
>>> move them to the swap-cache and to be able to return memory to the
>>> swap cache as soon as possible on a page-by-page basis.
>>> By reducing the page max order to the system PMD size, we can be
>>> nicer
>>> to the system and avoid splitting gigantic pages.
>>
>>> On top of this we also
>>> include the 64K page size in the page sizes tried, since that
>>> appears to
>>> be a common size for GPU applications.
>> Please completely drop that.
> You mean the 64K page size, or the whole patch?
The 64K page size. This was an invention from Microsoft to standardize
GPU handling ~15-20years ago.
It turned out to be a complete shipwreck and by now 2MiB and 1GiB pages
or just flexible hardware which can handle everything seem to become
standard.
>> This is just nonsense spilling in from the
>> Windows drivers.
> Agreed, but IIRC on the last RFC you asked me not to drop the 64K
> pages, so that's why they are here. I can remove them if needed.
We could keep it if it's in any way beneficial, but I'm pretty sure I
must have been drunk to ask for that.
> The only reason for keeping them from a performance point of view is
> better efficiency on GPUs with 64K page size if not using a coalescing
> IOMMU for dma-mapping.
Are any of those still produced? As far as I know neither NVidia, Intel
nor AMD still assumes that page size in their hardware for quite a while
now.
Regards,
Christian.
>
> Let me know what you think is best and I'll adjust accordingly.
>
> /Thomas
>
>
>> Christian.
>>
>>> Looking forward to when we might be able to swap out PMD size
>>> folios
>>> without splitting, this will also be a benefit.
>>>
>>> Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
>>> ---
>>> drivers/gpu/drm/ttm/ttm_pool.c | 58 ++++++++++++++++++++++++++---
>>> -----
>>> 1 file changed, 45 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/ttm/ttm_pool.c
>>> b/drivers/gpu/drm/ttm/ttm_pool.c
>>> index 1cc7591a9542..8787fb6a218b 100644
>>> --- a/drivers/gpu/drm/ttm/ttm_pool.c
>>> +++ b/drivers/gpu/drm/ttm/ttm_pool.c
>>> @@ -31,6 +31,8 @@
>>> * cause they are rather slow compared to alloc_pages+map.
>>> */
>>>
>>> +#define pr_fmt(fmt) "[TTM POOL] " fmt
>>> +
>>> #include <linux/module.h>
>>> #include <linux/dma-mapping.h>
>>> #include <linux/debugfs.h>
>>> @@ -47,6 +49,18 @@
>>>
>>> #include "ttm_module.h"
>>>
>>> +#define TTM_MAX_ORDER (PMD_SHIFT - PAGE_SHIFT)
>>> +#define TTM_64K_ORDER (16 - PAGE_SHIFT)
>>> +#if (TTM_MAX_ORDER < TTM_64K_ORDER)
>>> +#undef TTM_MAX_ORDER
>>> +#define TTM_MAX_ORDER TTM_64K_ORDER
>>> +#endif
>>> +#if ((MAX_ORDER - 1) < TTM_MAX_ORDER)
>>> +#undef TTM_MAX_ORDER
>>> +#define TTM_MAX_ORDER (MAX_ORDER - 1)
>>> +#endif
>>> +#define TTM_DIM_ORDER (TTM_MAX_ORDER + 1)
>>> +
>>> /**
>>> * struct ttm_pool_dma - Helper object for coherent DMA mappings
>>> *
>>> @@ -65,16 +79,18 @@ module_param(page_pool_size, ulong, 0644);
>>>
>>> static atomic_long_t allocated_pages;
>>>
>>> -static struct ttm_pool_type global_write_combined[MAX_ORDER];
>>> -static struct ttm_pool_type global_uncached[MAX_ORDER];
>>> +static struct ttm_pool_type global_write_combined[TTM_DIM_ORDER];
>>> +static struct ttm_pool_type global_uncached[TTM_DIM_ORDER];
>>>
>>> -static struct ttm_pool_type
>>> global_dma32_write_combined[MAX_ORDER];
>>> -static struct ttm_pool_type global_dma32_uncached[MAX_ORDER];
>>> +static struct ttm_pool_type
>>> global_dma32_write_combined[TTM_DIM_ORDER];
>>> +static struct ttm_pool_type global_dma32_uncached[TTM_DIM_ORDER];
>>>
>>> static spinlock_t shrinker_lock;
>>> static struct list_head shrinker_list;
>>> static struct shrinker mm_shrinker;
>>>
>>> +static unsigned int ttm_pool_orders[] = {TTM_MAX_ORDER, 0, 0};
>>> +
>>> /* Allocate pages of size 1 << order with the given gfp_flags */
>>> static struct page *ttm_pool_alloc_page(struct ttm_pool *pool,
>>> gfp_t gfp_flags,
>>> unsigned int order)
>>> @@ -400,6 +416,17 @@ static void __ttm_pool_free(struct ttm_pool
>>> *pool, struct ttm_tt *tt,
>>> }
>>> }
>>>
>>> +static unsigned int ttm_pool_select_order(unsigned int order,
>>> pgoff_t num_pages)
>>> +{
>>> + unsigned int *cur_order = ttm_pool_orders;
>>> +
>>> + order = min_t(unsigned int, __fls(num_pages), order);
>>> + while (order < *cur_order)
>>> + ++cur_order;
>>> +
>>> + return *cur_order;
>>> +}
>>> +
>>> /**
>>> * ttm_pool_alloc - Fill a ttm_tt object
>>> *
>>> @@ -439,9 +466,8 @@ int ttm_pool_alloc(struct ttm_pool *pool,
>>> struct ttm_tt *tt,
>>> else
>>> gfp_flags |= GFP_HIGHUSER;
>>>
>>> - for (order = min_t(unsigned int, MAX_ORDER - 1,
>>> __fls(num_pages));
>>> - num_pages;
>>> - order = min_t(unsigned int, order, __fls(num_pages)))
>>> {
>>> + order = ttm_pool_select_order(ttm_pool_orders[0],
>>> num_pages);
>>> + for (; num_pages; order = ttm_pool_select_order(order,
>>> num_pages)) {
>>> struct ttm_pool_type *pt;
>>>
>>> page_caching = tt->caching;
>>> @@ -558,7 +584,7 @@ void ttm_pool_init(struct ttm_pool *pool,
>>> struct device *dev,
>>>
>>> if (use_dma_alloc) {
>>> for (i = 0; i < TTM_NUM_CACHING_TYPES; ++i)
>>> - for (j = 0; j < MAX_ORDER; ++j)
>>> + for (j = 0; j < TTM_DIM_ORDER; ++j)
>>> ttm_pool_type_init(&pool-
>>>> caching[i].orders[j],
>>> pool, i, j);
>>> }
>>> @@ -578,7 +604,7 @@ void ttm_pool_fini(struct ttm_pool *pool)
>>>
>>> if (pool->use_dma_alloc) {
>>> for (i = 0; i < TTM_NUM_CACHING_TYPES; ++i)
>>> - for (j = 0; j < MAX_ORDER; ++j)
>>> + for (j = 0; j < TTM_DIM_ORDER; ++j)
>>> ttm_pool_type_fini(&pool-
>>>> caching[i].orders[j]);
>>> }
>>>
>>> @@ -632,7 +658,7 @@ static void ttm_pool_debugfs_header(struct
>>> seq_file *m)
>>> unsigned int i;
>>>
>>> seq_puts(m, "\t ");
>>> - for (i = 0; i < MAX_ORDER; ++i)
>>> + for (i = 0; i < TTM_DIM_ORDER; ++i)
>>> seq_printf(m, " ---%2u---", i);
>>> seq_puts(m, "\n");
>>> }
>>> @@ -643,7 +669,7 @@ static void ttm_pool_debugfs_orders(struct
>>> ttm_pool_type *pt,
>>> {
>>> unsigned int i;
>>>
>>> - for (i = 0; i < MAX_ORDER; ++i)
>>> + for (i = 0; i < TTM_DIM_ORDER; ++i)
>>> seq_printf(m, " %8u", ttm_pool_type_count(&pt[i]));
>>> seq_puts(m, "\n");
>>> }
>>> @@ -749,10 +775,16 @@ int ttm_pool_mgr_init(unsigned long
>>> num_pages)
>>> if (!page_pool_size)
>>> page_pool_size = num_pages;
>>>
>>> + if (TTM_64K_ORDER < TTM_MAX_ORDER)
>>> + ttm_pool_orders[1] = TTM_64K_ORDER;
>>> +
>>> + pr_debug("Used orders are %u %u %u\n", ttm_pool_orders[0],
>>> + ttm_pool_orders[1], ttm_pool_orders[2]);
>>> +
>>> spin_lock_init(&shrinker_lock);
>>> INIT_LIST_HEAD(&shrinker_list);
>>>
>>> - for (i = 0; i < MAX_ORDER; ++i) {
>>> + for (i = 0; i < TTM_DIM_ORDER; ++i) {
>>> ttm_pool_type_init(&global_write_combined[i], NULL,
>>> ttm_write_combined, i);
>>> ttm_pool_type_init(&global_uncached[i], NULL,
>>> ttm_uncached, i);
>>> @@ -785,7 +817,7 @@ void ttm_pool_mgr_fini(void)
>>> {
>>> unsigned int i;
>>>
>>> - for (i = 0; i < MAX_ORDER; ++i) {
>>> + for (i = 0; i < TTM_DIM_ORDER; ++i) {
>>> ttm_pool_type_fini(&global_write_combined[i]);
>>> ttm_pool_type_fini(&global_uncached[i]);
>>>
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