git: 7fd88ba72eb3 - stable/13 - netgraph/ng_bridge: Avoid cache thrashing

[Lutz Donnerhacke]

The branch stable/13 has been updated by donner:

URL: https://cgit.FreeBSD.org/src/commit/?id=7fd88ba72eb353c9dd43063f5faea019ad5b0ea9

commit 7fd88ba72eb353c9dd43063f5faea019ad5b0ea9
Author:     Lutz Donnerhacke <donner at FreeBSD.org>
AuthorDate: 2021-02-11 22:59:11 +0000
Commit:     Lutz Donnerhacke <donner at FreeBSD.org>
CommitDate: 2021-05-27 10:55:52 +0000

    netgraph/ng_bridge: Avoid cache thrashing
    
    Hint the compiler, that this update is needed at most once per second.
    Only in this case the memory line needs to be written.  This will
    reduce the amount of cache trashing during forward of most frames.
    
    Suggested by:   zec
    Approved by:    zec
    Differential Revision:  https://reviews.freebsd.org/D28601
    
    (cherry picked from commit 4dfe70fdbda05453e824bc9edfc0d09eab7b2929)
---
 sys/netgraph/ng_bridge.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sys/netgraph/ng_bridge.c b/sys/netgraph/ng_bridge.c
index 0bed50fc240b..baedeb911e6d 100644
--- a/sys/netgraph/ng_bridge.c
+++ b/sys/netgraph/ng_bridge.c
@@ -863,7 +863,8 @@ ng_bridge_rcvdata(hook_p hook, item_p item)
 		 * This is safe without locking, because it's
 		 * the only operation during shared access.
 		 */
-		host->staleness = 0;
+		if (__predict_false(host->staleness > 0))
+			host->staleness = 0;
 
 	if ((host == NULL && ctx.incoming->learnMac) ||
 	    (host != NULL && host->link != ctx.incoming)) {