Hi Ian,
Could you please review the below version of the patch and provide the
comments?
All the comments which were given in the previous versions are incorporated.
Thanks,
Aravindan
> -----Original Message-----
> From: Muthukumar, Aravindan
> Sent: Thursday, November 9, 2017 11:15 AM
> To: mesa-dev@lists.freedesktop.org
> Cc: Muthukumar, Aravindan <aravindan.muthuku...@intel.com>; J Karanje,
> Kedar <kedar.j.kara...@intel.com>
> Subject: [PATCH v4] i965 : optimized bucket index calculation
>
> From: Aravindan Muthukumar <aravindan.muthuku...@intel.com>
>
> Reducing Bucket index calculation to O(1).
>
> This algorithm calculates the index using matrix method.
> Matrix arrangement is as below:
> Assuming PAGE_SIZE is 4096.
>
> 1*4096 2*4096 3*4096 4*4096
> 5*4096 6*4096 7*4096 8*4096
> 10*4096 12*4096 14*4096 16*4096
> 20*4096 24*4096 28*4096 32*4096
> ... ... ... ...
> ... ... ... ...
> ... ... ... max_cache_size
>
> From this matrix its clearly seen that every row follows the below way:
> ... ... ... n
> n+(1/4)n n+(1/2)n n+(3/4)n 2n
>
> Row is calculated as log2(size/PAGE_SIZE) Column is calculated as converting
> the difference between the elements to fit into power size of two and indexing
> it.
>
> Final Index is (row*4)+(col-1)
>
> Tested with Intel Mesa CI.
>
> Improves performance of 3DMark on BXT by 0.705966% +/- 0.229767% (n=20)
>
> v4: Review comments on style and code comments implemented (Ian).
> v3: Review comments implemented (Ian).
> v2: Review comments implemented (Jason).
>
> Signed-off-by: Aravindan Muthukumar <aravindan.muthuku...@intel.com>
> Signed-off-by: Kedar Karanje <kedar.j.kara...@intel.com>
> Reviewed-by: Yogesh Marathe <yogesh.mara...@intel.com>
> ---
> src/mesa/drivers/dri/i965/brw_bufmgr.c | 47
> ++++++++++++++++++++++++++++------
> 1 file changed, 39 insertions(+), 8 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.c
> b/src/mesa/drivers/dri/i965/brw_bufmgr.c
> index 17036b5..f21df5a 100644
> --- a/src/mesa/drivers/dri/i965/brw_bufmgr.c
> +++ b/src/mesa/drivers/dri/i965/brw_bufmgr.c
> @@ -86,6 +86,8 @@
>
> #define memclear(s) memset(&s, 0, sizeof(s))
>
> +#define PAGE_SIZE 4096
> +
> #define FILE_DEBUG_FLAG DEBUG_BUFMGR
>
> static inline int
> @@ -180,19 +182,44 @@ bo_tile_pitch(struct brw_bufmgr *bufmgr, uint32_t
> pitch, uint32_t tiling)
> return ALIGN(pitch, tile_width);
> }
>
> +/**
> + * This function finds the correct bucket fit for the input size.
> + * The function works with O(1) complexity when the requested size
> + * was queried instead of iterating the size through all the buckets.
> + */
> static struct bo_cache_bucket *
> bucket_for_size(struct brw_bufmgr *bufmgr, uint64_t size) {
> - int i;
> + /* Calculating the pages and rounding up to the page size. */
> + const unsigned pages = (size + PAGE_SIZE - 1) / PAGE_SIZE;
> +
> + /* Row Bucket sizes clz((x-1) | 3) Row Column
> + * in pages stride size
> + * 0: 1 2 3 4 -> 30 30 30 30 4 1
> + * 1: 5 6 7 8 -> 29 29 29 29 4 1
> + * 2: 10 12 14 16 -> 28 28 28 28 8 2
> + * 3: 20 24 28 32 -> 27 27 27 27 16 4
> + */
> + const unsigned row = 30 - __builtin_clz((pages - 1) | 3);
> + const unsigned row_max_pages = 4 << row;
> +
> + /* The '& ~2' is the special case for row 1. In row 1, max pages /
> + * 2 is 2, but the previous row maximum is zero (because there is
> + * no previous row). All row maximum sizes are power of 2, so that
> + * is the only case where that bit will be set.
> + */
> + const unsigned prev_row_max_pages = (row_max_pages / 2) & ~2;
> + int col_size_log2 = row - 1;
> + col_size_log2 += (col_size_log2 < 0);
>
> - for (i = 0; i < bufmgr->num_buckets; i++) {
> - struct bo_cache_bucket *bucket = &bufmgr->cache_bucket[i];
> - if (bucket->size >= size) {
> - return bucket;
> - }
> - }
> + const unsigned col = (pages - prev_row_max_pages +
> + ((1 << col_size_log2) - 1)) >> col_size_log2;
>
> - return NULL;
> + /* Calculating the index based on the row and column. */
> + const unsigned index = (row * 4) + (col - 1);
> +
> + return (index < bufmgr->num_buckets) ?
> + &bufmgr->cache_bucket[index] : NULL;
> }
>
> int
> @@ -1254,6 +1281,10 @@ add_bucket(struct brw_bufmgr *bufmgr, int size)
> list_inithead(&bufmgr->cache_bucket[i].head);
> bufmgr->cache_bucket[i].size = size;
> bufmgr->num_buckets++;
> +
> + assert(bucket_for_size(bufmgr, size) == &bufmgr->cache_bucket[i]);
> + assert(bucket_for_size(bufmgr, size - 2048) == &bufmgr->cache_bucket[i]);
> + assert(bucket_for_size(bufmgr, size + 1) !=
> + &bufmgr->cache_bucket[i]);
> }
>
> static void
> --
> 2.7.4
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