In general, I'm very concerned about how this handles rounding behavior.
Almost everywhere, you round down when what you want to do is round up.
Also, as I said on IRC, I'd like to see some asserts in add_bucket so that
we are sure this calculation is correct. In particular, I'd like to see
assert(bucket_for_size(size) == &bufmgr->cache_bucket[i]);
assert(bucket_for_size(size - 2048) == &bufmgr->cache_bucket[i]);
assert(bucket_for_size(size + 1) != &bufmgr->cache_bucket[i]);
We need to check on both sides of size to be 100% sure we're doing our
rounding correctly.
On Fri, Sep 8, 2017 at 1:11 AM, <aravindan.muthuku...@intel.com> wrote:
> From: Aravindan Muthukumar <aravindan.muthuku...@intel.com>
>
> Avoiding the loop which was running with O(n) complexity.
> Now the complexity has been reduced to O(1)
>
> Tested with piglit.
> Slight performance improvement (~1%) in 3d mark.
>
Which 3dmark test? Also, what's the error in that 1%?
> Change-Id: Id099f1cd24ad5b691a69070eda79b8f4e9be39a6
> 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 | 48
> +++++++++++++++++++++++++++++-----
> 1 file changed, 41 insertions(+), 7 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.c
> b/src/mesa/drivers/dri/i965/brw_bufmgr.c
> index 5b4e784..18cb166 100644
> --- a/src/mesa/drivers/dri/i965/brw_bufmgr.c
> +++ b/src/mesa/drivers/dri/i965/brw_bufmgr.c
> @@ -87,6 +87,11 @@
>
> #define memclear(s) memset(&s, 0, sizeof(s))
>
> +/* Macros for BO cache size */
> +#define CACHE_PAGE_SIZE 4096
>
Just call this PAGE_SIZE
> +#define PAGE_SIZE_SHIFT 12
> +#define BO_CACHE_PAGE_SIZE (4 * CACHE_PAGE_SIZE)
>
I think I'd rather we just use 4 * PAGE_SIZE explicitly than have this
extra #define. I think it's making things harder to read and not easier.
> +
> #define FILE_DEBUG_FLAG DEBUG_BUFMGR
>
> static inline int
> @@ -181,19 +186,48 @@ bo_tile_pitch(struct brw_bufmgr *bufmgr, uint32_t
> pitch, uint32_t tiling)
> return ALIGN(pitch, tile_width);
> }
>
> +/*
> + * This functions is to find the correct bucket fit for the input size.
> + * This 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;
> + struct bo_cache_bucket *bucket = NULL;
> + int x=0,index = -1;
> + int row, col=0;
>
> - for (i = 0; i < bufmgr->num_buckets; i++) {
> - struct bo_cache_bucket *bucket = &bufmgr->cache_bucket[i];
> - if (bucket->size >= size) {
> - return bucket;
> - }
> + /* condition for size less than 4*4096 (4KB) page size */
> + if(size < BO_CACHE_PAGE_SIZE){
>
This should be "<="
> + index = (size>>PAGE_SIZE_SHIFT)+((size%(1<<PAGE_SIZE_SHIFT)?1:0)
> )-1;
>
I agree with tapani, that this can easily be an early return.
I think we can also make this calculation a lot more clear:
index = DIV_ROUND_UP(size, PAGE_SIZE) - 1;
> }
> + else{
> + /* When the size is more than 4*4096, the logic follows a matrix
> method
> + * where the index will be searched using Arithmetico-Geometric
> progression.
> + * So the given size will be divided by 4096 & the index will be
> traced out.
> + */
> + x = size>>PAGE_SIZE_SHIFT;
>
This rounds down not up like you want.
> - return NULL;
> + /* Find the row using Geometric Progression. The highest bit set
> will give
> + * the row number. num = a * r^(n-1) where num = size a = 4 r = 2
> + */
> + row = 31 - __builtin_clz(x>>1);
> +
> + /* Find the column using AP but using the row value
> + * calculated using GP.
> + */
> + col =((x-(1<<(row+1)))/(1<<(row-1)))+1;
> + col += (size%(1<<PAGE_SIZE_SHIFT<<(row-1)))?1:0;
> +
> + /* Finding the index value using calculated row and col number */
> + index = ((row-1)<<2) + col + 2;
>
I think this can probably also be a lot simpler. How about something like
this:
pages = DIV_ROUND_UP(size, PAGE_SIZE);
/* Steal this from anv_allocator.c */
pages_log2 = ilog2_round_up(pages);
row = pages_log2 - 1;
col = DIV_ROUND_UP(pages, (1 << (pages_log2 - 2)));
index = row * 4 + col;
+ }
> +
> + /* Checking the error condition */
> + bucket = (index >= 0 && index < bufmgr->num_buckets)?(&bufmgr-
> >cache_bucket[index]):NULL;
> + return bucket;
> }
>
> int
> --
> 2.7.4
>
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