Hi,
When creating network load by forwarding packets, SSH gets unusable
and ping time gets above 10 seconds.
Problem is that while multiple forwarding threads are running with
shared net lock, the exclusive lock cannot be acquired. This is
unfair.
Diff below prevents that a read lock is granted when another thread
is waiting for the exclusive lock. With that ping time stays under
300 ms.
Does this read write lock prio change make sense?
bluhm
Index: kern/kern_rwlock.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/kern/kern_rwlock.c,v
retrieving revision 1.47
diff -u -p -r1.47 kern_rwlock.c
--- kern/kern_rwlock.c 8 Feb 2021 08:18:45 -0000 1.47
+++ kern/kern_rwlock.c 6 May 2022 12:08:01 -0000
@@ -81,7 +81,7 @@ static const struct rwlock_op {
},
{ /* RW_READ */
RWLOCK_READ_INCR,
- RWLOCK_WRLOCK,
+ RWLOCK_WRLOCK | RWLOCK_WRWANT,
RWLOCK_WAIT,
0,
PLOCK
@@ -103,7 +103,7 @@ rw_enter_read(struct rwlock *rwl)
{
unsigned long owner = rwl->rwl_owner;
- if (__predict_false((owner & RWLOCK_WRLOCK) ||
+ if (__predict_false((owner & (RWLOCK_WRLOCK | RWLOCK_WRWANT)) ||
rw_cas(&rwl->rwl_owner, owner, owner + RWLOCK_READ_INCR)))
rw_enter(rwl, RW_READ);
else {
