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Micro-optimize the page count computations in scst_mem.c by

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rewriting these computations such that branch instructions are avoided.

BSD-signed-off-by: Bart Van Assche <bvanassche@acm.org>



git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@3963 d57e44dd-8a1f-0410-8b47-8ef2f437770f
This commit is contained in:
Vladislav Bolkhovitin
2011-12-08 00:06:24 +00:00
parent cd2d549a0b
commit f173a9133c
1 changed files with 7 additions and 12 deletions
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19
scst/src/scst_mem.c
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@@ -544,8 +544,7 @@ static void sgv_free_sys_sg_entries(struct scatterlist *sg, int sg_count,
for (i = 0; i < sg_count; i++) {
struct page *p = sg_page(&sg[i]);
int len = sg[i].length;
int pages =
(len >> PAGE_SHIFT) + ((len & ~PAGE_MASK) != 0);
int pages = PAGE_ALIGN(len) >> PAGE_SHIFT;
TRACE_MEM("page %lx, len %d, pages %d",
(unsigned long)p, len, pages);
@@ -632,8 +631,7 @@ static int sgv_alloc_sg_entries(struct scatterlist *sg, int pages,
if ((clustering_type != sgv_no_clustering) && (trans_tbl != NULL)) {
pg = 0;
for (i = 0; i < pages; i++) {
int n = (sg[i].length >> PAGE_SHIFT) +
((sg[i].length & ~PAGE_MASK) != 0);
int n = PAGE_ALIGN(sg[i].length) >> PAGE_SHIFT;
trans_tbl[i].pg_count = pg;
for (j = 0; j < n; j++)
trans_tbl[pg++].sg_num = i+1;
@@ -926,7 +924,7 @@ struct scatterlist *sgv_pool_alloc(struct sgv_pool *pool, unsigned int size,
EXTRACHECKS_BUG_ON((gfp_mask & __GFP_NOFAIL) == __GFP_NOFAIL);
pages = ((size + PAGE_SIZE - 1) >> PAGE_SHIFT);
pages = PAGE_ALIGN(size) >> PAGE_SHIFT;
if (pool->single_alloc_pages == 0) {
int pages_order = get_order(size);
cache_num = pages_order;
@@ -1103,9 +1101,7 @@ success:
res = obj->sg_entries;
*sgv = obj;
if (size & ~PAGE_MASK)
obj->sg_entries[cnt-1].length -=
PAGE_SIZE - (size & ~PAGE_MASK);
obj->sg_entries[cnt-1].length -= PAGE_ALIGN(size) - size;
TRACE_MEM("obj=%p, sg_entries %p (size=%d, pages=%d, sg_count=%d, "
"count=%d, last_len=%d)", obj, obj->sg_entries, size, pages,
@@ -1211,7 +1207,7 @@ void sgv_pool_free(struct sgv_pool_obj *obj, struct scst_mem_lim *mem_lim)
for (i = 0; i < obj->sg_count; i++) {
struct page *p = sg_page(&sg[i]);
int len = sg[i].length;
int pages = (len >> PAGE_SHIFT) + ((len & ~PAGE_MASK) != 0);
int pages = PAGE_ALIGN(len) >> PAGE_SHIFT;
while (pages > 0) {
if (atomic_read(&p->_count) != 1) {
PRINT_WARNING("Freeing page %p with "
@@ -1252,7 +1248,7 @@ EXPORT_SYMBOL_GPL(sgv_pool_free);
struct scatterlist *scst_alloc(int size, gfp_t gfp_mask, int *count)
{
struct scatterlist *res;
int pages = (size >> PAGE_SHIFT) + ((size & ~PAGE_MASK) != 0);
int pages = PAGE_ALIGN(size) >> PAGE_SHIFT;
struct sgv_pool_alloc_fns sys_alloc_fns = {
sgv_alloc_sys_pages, sgv_free_sys_sg_entries };
int no_fail = ((gfp_mask & __GFP_NOFAIL) == __GFP_NOFAIL);
@@ -1295,8 +1291,7 @@ struct scatterlist *scst_alloc(int size, gfp_t gfp_mask, int *count)
if (cnt <= 0)
goto out_free;
if (size & ~PAGE_MASK)
res[cnt-1].length -= PAGE_SIZE - (size & ~PAGE_MASK);
res[cnt-1].length -= PAGE_ALIGN(size) - size;
*count = cnt;