git: d7cde43f95bf - main - Revert "loopback: Clear hash unconditionally."

The branch main has been updated by gallatin:

URL: https://cgit.FreeBSD.org/src/commit/?id=d7cde43f95bf432b6894c3cf804a8dffe99461e4

commit d7cde43f95bf432b6894c3cf804a8dffe99461e4
Author:     Andrew Gallatin <gallatin@FreeBSD.org>
AuthorDate: 2026-05-21 13:28:46 +0000
Commit:     Andrew Gallatin <gallatin@FreeBSD.org>
CommitDate: 2026-05-21 13:34:40 +0000

    Revert "loopback: Clear hash unconditionally."
    
    This reverts commit 2fe37927d41990abe8d1c336e75fd75873285e90.
    
    This turns out to have been misguided.  First, clearing the
    hash results in all loopback ip/ip6 traffic being hashed
    to the netisr queue associated with the if_index of the loopback
    interface.  Eg, it bottlenecks loopback traffic. When the
    hash is kept, traffic is spread evenly among netisrs.
    
    Also, it is safe to keep the hash here.  The clearing was only
    needed when RSS core selection is enabled; we only enabled the
    consistent hashing parts of RSS globally, not the cpuid mapping
    stuff.  So there is no need to clear it.
    
    Reviewed by: glebius
    Sponsored by: Netflix
---
 sys/net/if_loop.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sys/net/if_loop.c b/sys/net/if_loop.c
index 33ddd3a8540e..fc5ce9548bcc 100644
--- a/sys/net/if_loop.c
+++ b/sys/net/if_loop.c
@@ -219,7 +219,9 @@ looutput(struct ifnet *ifp, struct mbuf *m, const struct sockaddr *dst,
 	if_inc_counter(ifp, IFCOUNTER_OPACKETS, 1);
 	if_inc_counter(ifp, IFCOUNTER_OBYTES, m->m_pkthdr.len);
 
+#ifdef RSS
 	M_HASHTYPE_CLEAR(m);
+#endif
 
 	/* BPF writes need to be handled specially. */
 	if (dst->sa_family == AF_UNSPEC || dst->sa_family == pseudo_AF_HDRCMPLT)