On Fri, Oct 18, 2019 at 03:55:39PM +1000, David Gwynne wrote:
> why? is it significantly faster? page allocation should be in the slow path.
At least it was not slower. Performance were slightly higher, but
changes are well below meassurement tolerance.
Usually it is a good idea to avoid locks and mutexes if possible.
Atomic operations cannot create deadlocks.
In this case the code becomes shorter.
I have put back the unprotected check in m_pool_alloc(). It avoids
possibly expensive atomic operations. Do we want this? I could
not measure any difference.
bluhm
Index: kern/uipc_mbuf.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/kern/uipc_mbuf.c,v
retrieving revision 1.272
diff -u -p -r1.272 uipc_mbuf.c
--- kern/uipc_mbuf.c 19 Jul 2019 09:03:03 -0000 1.272
+++ kern/uipc_mbuf.c 18 Oct 2019 12:33:43 -0000
@@ -133,7 +133,6 @@ struct mutex m_extref_mtx = MUTEX_INITIA
void m_extfree(struct mbuf *);
void m_zero(struct mbuf *);
-struct mutex m_pool_mtx = MUTEX_INITIALIZER(IPL_NET);
unsigned long mbuf_mem_limit; /* how much memory can be allocated */
unsigned long mbuf_mem_alloc; /* how much memory has been allocated */
@@ -1473,30 +1472,23 @@ m_microtime(const struct mbuf *m, struct
void *
m_pool_alloc(struct pool *pp, int flags, int *slowdown)
{
- void *v = NULL;
- int avail = 1;
+ void *v;
+ long alloc;
if (mbuf_mem_alloc + pp->pr_pgsize > mbuf_mem_limit)
return (NULL);
- mtx_enter(&m_pool_mtx);
- if (mbuf_mem_alloc + pp->pr_pgsize > mbuf_mem_limit)
- avail = 0;
- else
- mbuf_mem_alloc += pp->pr_pgsize;
- mtx_leave(&m_pool_mtx);
-
- if (avail) {
- v = (*pool_allocator_multi.pa_alloc)(pp, flags, slowdown);
+ alloc = atomic_add_long_nv(&mbuf_mem_alloc, pp->pr_pgsize);
+ if (alloc > mbuf_mem_limit)
+ goto fail;
- if (v == NULL) {
- mtx_enter(&m_pool_mtx);
- mbuf_mem_alloc -= pp->pr_pgsize;
- mtx_leave(&m_pool_mtx);
- }
- }
+ v = (*pool_allocator_multi.pa_alloc)(pp, flags, slowdown);
+ if (v != NULL)
+ return (v);
- return (v);
+ fail:
+ atomic_sub_long(&mbuf_mem_alloc, pp->pr_pgsize);
+ return (NULL);
}
void
@@ -1504,9 +1496,7 @@ m_pool_free(struct pool *pp, void *v)
{
(*pool_allocator_multi.pa_free)(pp, v);
- mtx_enter(&m_pool_mtx);
- mbuf_mem_alloc -= pp->pr_pgsize;
- mtx_leave(&m_pool_mtx);
+ atomic_sub_long(&mbuf_mem_alloc, pp->pr_pgsize);
}
void
