Module Name: src
Committed By: riastradh
Date: Wed Aug 9 08:38:16 UTC 2023
Modified Files:
src/sys/arch/xen/xen: xennetback_xenbus.c
Log Message:
xvif(4): Move expensive xen_mb out of xennetback_evthandler loop.
Use the cheaper RING_HAS_UNCONFIRMED_REQUESTS for most of the loop.
This should improve throughput without any impact on correctness.
To generate a diff of this commit:
cvs rdiff -u -r1.118 -r1.119 src/sys/arch/xen/xen/xennetback_xenbus.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/arch/xen/xen/xennetback_xenbus.c
diff -u src/sys/arch/xen/xen/xennetback_xenbus.c:1.118 src/sys/arch/xen/xen/xennetback_xenbus.c:1.119
--- src/sys/arch/xen/xen/xennetback_xenbus.c:1.118 Wed Aug 9 08:38:05 2023
+++ src/sys/arch/xen/xen/xennetback_xenbus.c Wed Aug 9 08:38:16 2023
@@ -1,4 +1,4 @@
-/* $NetBSD: xennetback_xenbus.c,v 1.118 2023/08/09 08:38:05 riastradh Exp $ */
+/* $NetBSD: xennetback_xenbus.c,v 1.119 2023/08/09 08:38:16 riastradh Exp $ */
/*
* Copyright (c) 2006 Manuel Bouyer.
@@ -25,7 +25,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: xennetback_xenbus.c,v 1.118 2023/08/09 08:38:05 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: xennetback_xenbus.c,v 1.119 2023/08/09 08:38:16 riastradh Exp $");
#include <sys/types.h>
#include <sys/param.h>
@@ -811,6 +811,7 @@ xennetback_evthandler(void *arg)
(IFF_UP | IFF_RUNNING));
XENPRINTF(("xennetback_evthandler "));
+again:
while (1) {
/*
* XXX The xen_rmb here and comment make no sense:
@@ -819,16 +820,7 @@ xennetback_evthandler(void *arg)
xen_rmb(); /* be sure to read the request before updating */
/* XXX Unclear what this xen_wmb is for. */
xen_wmb();
- /*
- * XXX RING_FINAL_CHECK_FOR_REQUESTS issues the most
- * expensive memory barrier, xen_mb. This should be
- * used only at the end of the loop after we updating
- * the producer with the last index of the requests we
- * consumed in the queue.
- */
- RING_FINAL_CHECK_FOR_REQUESTS(&xneti->xni_txring,
- receive_pending);
- if (receive_pending == 0)
+ if (!RING_HAS_UNCONSUMED_REQUESTS(&xneti->xni_txring))
break;
/*
* Ensure we have read the producer's queue index in
@@ -981,6 +973,9 @@ mbuf_fail:
queued = 0;
}
}
+ RING_FINAL_CHECK_FOR_REQUESTS(&xneti->xni_txring, receive_pending);
+ if (receive_pending)
+ goto again;
if (m0) {
/* Queue empty, and still unfinished multi-fragment request */
printf("%s: dropped unfinished multi-fragment\n",
