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authorFred Klassen <fklassen@appneta.com>2019-06-17 12:05:07 -0700
committerDavid S. Miller <davem@davemloft.net>2019-06-18 21:38:07 -0400
commit76e21533a48bb42d1fa894f93f6233bf4554f45e (patch)
parente11e1007a177fe4abc12b620dcf9e36eb8027f40 (diff)
net/udp_gso: Allow TX timestamp with UDP GSO
Fixes an issue where TX Timestamps are not arriving on the error queue when UDP_SEGMENT CMSG type is combined with CMSG type SO_TIMESTAMPING. This can be illustrated with an updated updgso_bench_tx program which includes the '-T' option to test for this condition. It also introduces the '-P' option which will call poll() before reading the error queue. ./udpgso_bench_tx -4ucTPv -S 1472 -l2 -D poll timeout udp tx: 0 MB/s 1 calls/s 1 msg/s The "poll timeout" message above indicates that TX timestamp never arrived. This patch preserves tx_flags for the first UDP GSO segment. Only the first segment is timestamped, even though in some cases there may be benefital in timestamping both the first and last segment. Factors in deciding on first segment timestamp only: - Timestamping both first and last segmented is not feasible. Hardware can only have one outstanding TS request at a time. - Timestamping last segment may under report network latency of the previous segments. Even though the doorbell is suppressed, the ring producer counter has been incremented. - Timestamping the first segment has the upside in that it reports timestamps from the application's view, e.g. RTT. - Timestamping the first segment has the downside that it may underreport tx host network latency. It appears that we have to pick one or the other. And possibly follow-up with a config flag to choose behavior. v2: Remove tests as noted by Willem de Bruijn <willemb@google.com> Moving tests from net to net-next v3: Update only relevant tx_flag bits as per Willem de Bruijn <willemb@google.com> v4: Update comments and commit message as per Willem de Bruijn <willemb@google.com> Fixes: ee80d1ebe5ba ("udp: add udp gso") Signed-off-by: Fred Klassen <fklassen@appneta.com> Acked-by: Willem de Bruijn <willemb@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
1 files changed, 5 insertions, 0 deletions
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 06b3e2c1fcdc..9763464a75d7 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -224,6 +224,11 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
seg = segs;
uh = udp_hdr(seg);
+ /* preserve TX timestamp flags and TS key for first segment */
+ skb_shinfo(seg)->tskey = skb_shinfo(gso_skb)->tskey;
+ skb_shinfo(seg)->tx_flags |=
+ (skb_shinfo(gso_skb)->tx_flags & SKBTX_ANY_TSTAMP);
/* compute checksum adjustment based on old length versus new */
newlen = htons(sizeof(*uh) + mss);
check = csum16_add(csum16_sub(uh->check, uh->len), newlen);