Call slowpath __slab_alloc() from within the bulk loop, as the
side-effect of this call likely repopulates c->freelist.
Choose to reenable local IRQs while calling slowpath.
Saving some optimizations for later. E.g. it is possible to
extract parts of __slab_alloc() and avoid the unnecessary and
expensive (37 cycles) local_irq_{save,restore}. For now, be
happy calling __slab_alloc() this lower icache impact of this
func and I don't have to worry about correctness.
Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
---
V2:
- remove update of "tid" before call to __slab_alloc()
not necessary as code-path does not modify per cpu information
Measurements on CPU CPU i7-4790K @ 4.00GHz
Baseline normal fastpath (alloc+free cost): 42 cycles(tsc) 10.601 ns
Bulk- fallback - this-patch
1 - 58 cycles(tsc) 14.516 ns - 49 cycles(tsc) 12.459 ns improved 15.5%
2 - 51 cycles(tsc) 12.930 ns - 38 cycles(tsc) 9.605 ns improved 25.5%
3 - 49 cycles(tsc) 12.274 ns - 34 cycles(tsc) 8.525 ns improved 30.6%
4 - 48 cycles(tsc) 12.058 ns - 32 cycles(tsc) 8.036 ns improved 33.3%
8 - 46 cycles(tsc) 11.609 ns - 31 cycles(tsc) 7.756 ns improved 32.6%
16 - 45 cycles(tsc) 11.451 ns - 32 cycles(tsc) 8.148 ns improved 28.9%
30 - 79 cycles(tsc) 19.865 ns - 68 cycles(tsc) 17.164 ns improved 13.9%
32 - 76 cycles(tsc) 19.212 ns - 66 cycles(tsc) 16.584 ns improved 13.2%
34 - 74 cycles(tsc) 18.600 ns - 63 cycles(tsc) 15.954 ns improved 14.9%
48 - 88 cycles(tsc) 22.092 ns - 77 cycles(tsc) 19.373 ns improved 12.5%
64 - 80 cycles(tsc) 20.043 ns - 68 cycles(tsc) 17.188 ns improved 15.0%
128 - 99 cycles(tsc) 24.818 ns - 89 cycles(tsc) 22.404 ns improved 10.1%
158 - 99 cycles(tsc) 24.977 ns - 92 cycles(tsc) 23.089 ns improved 7.1%
250 - 106 cycles(tsc) 26.552 ns - 99 cycles(tsc) 24.785 ns improved 6.6%
mm/slub.c | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index a92fdec57237..02c33bacd3a6 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2779,8 +2779,22 @@ bool kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
for (i = 0; i < size; i++) {
void *object = c->freelist;
- if (!object)
- break;
+ if (unlikely(!object)) {
+ local_irq_enable();
+ /*
+ * Invoking slow path likely have side-effect
+ * of re-populating per CPU c->freelist
+ */
+ p[i] = __slab_alloc(s, flags, NUMA_NO_NODE,
+ _RET_IP_, c);
+ if (unlikely(!p[i])) {
+ __kmem_cache_free_bulk(s, i, p);
+ return false;
+ }
+ local_irq_disable();
+ c = this_cpu_ptr(s->cpu_slab);
+ continue; /* goto for-loop */
+ }
c->freelist = get_freepointer(s, object);
p[i] = object;
@@ -2796,14 +2810,6 @@ bool kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
memset(p[j], 0, s->object_size);
}
- /* Fallback to single elem alloc */
- for (; i < size; i++) {
- void *x = p[i] = kmem_cache_alloc(s, flags);
- if (unlikely(!x)) {
- __kmem_cache_free_bulk(s, i, p);
- return false;
- }
- }
return true;
}
EXPORT_SYMBOL(kmem_cache_alloc_bulk);
--
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