On Mon, Dec 28, 2020 at 02:45:06PM +1000, David Gwynne wrote:
> now that bpf read timeouts are only handled on the bpfread() side,
> there's a simplification that can be made in bpf_catchpacket. the chunk
> in bpf_catchpacket that rotates the buffers when one gets full already
> does a wakeup, so we don't have to check if we have any waiting readers
> and wake them up when a buffer gets full.
>
> we can use bd_nreaders to omgoptimise bpf_wakeup though. wakeup(9) is
> mpsafe, so we don't have to defer the call to a task. however, we can
> avoid calling wakeup() and therefore trying to take the sched lock and
> all that stuff when we know there's nothing sleeping.
>
> this also avoids scheduling the task if there's no async stuff set up.
> it's a bit magical because it knows what's inside selwakeup.
>
> tests? ok?
visa pointed out that i missed a bit relating to kq.
Index: bpf.c
===================================================================
RCS file: /cvs/src/sys/net/bpf.c,v
retrieving revision 1.199
diff -u -p -r1.199 bpf.c
--- bpf.c 26 Dec 2020 16:30:58 -0000 1.199
+++ bpf.c 29 Dec 2020 06:04:58 -0000
@@ -554,7 +554,6 @@ out:
return (error);
}
-
/*
* If there are processes sleeping on this descriptor, wake them up.
*/
@@ -563,14 +562,20 @@ bpf_wakeup(struct bpf_d *d)
{
MUTEX_ASSERT_LOCKED(&d->bd_mtx);
+ if (d->bd_nreaders)
+ wakeup(d);
+
/*
* As long as pgsigio() and selwakeup() need to be protected
* by the KERNEL_LOCK() we have to delay the wakeup to
* another context to keep the hot path KERNEL_LOCK()-free.
*/
- bpf_get(d);
- if (!task_add(systq, &d->bd_wake_task))
- bpf_put(d);
+ if ((d->bd_async && d->bd_sig) ||
+ (!klist_empty(&d->bd_sel.si_note) || d->bd_sel.si_seltid != 0)) {
+ bpf_get(d);
+ if (!task_add(systq, &d->bd_wake_task))
+ bpf_put(d);
+ }
}
void
@@ -578,7 +583,6 @@ bpf_wakeup_cb(void *xd)
{
struct bpf_d *d = xd;
- wakeup(d);
if (d->bd_async && d->bd_sig)
pgsigio(&d->bd_sigio, d->bd_sig, 0);
@@ -1542,17 +1546,6 @@ bpf_catchpacket(struct bpf_d *d, u_char
* reads should be woken up.
*/
do_wakeup = 1;
- }
-
- if (d->bd_nreaders > 0) {
- /*
- * We have one or more threads sleeping in bpfread().
- * We got a packet, so wake up all readers.
- */
- if (d->bd_fbuf != NULL) {
- ROTATE_BUFFERS(d);
- do_wakeup = 1;
- }
}
if (do_wakeup)
