Messages in this thread | | | Date | Thu, 9 Nov 2023 12:16:06 -0500 | Subject | Re: [PATCH 01/41] rxrpc: Fix RTT determination to use PING ACKs as a source | From | Jeffrey E Altman <> |
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On 11/9/2023 10:39 AM, David Howells wrote: > Fix RTT determination to use a PING ACK that is in marked as being in > response to a DATA packet as the response from which RTT can be calculated > from in lieu of a REQUESTED ACK. The server may send the latter instead of > the former. > > Fixes: 4700c4d80b7b ("rxrpc: Fix loss of RTT samples due to interposed ACK") > Signed-off-by: David Howells <dhowells@redhat.com> > cc: Marc Dionne <marc.dionne@auristor.com> > cc: linux-afs@lists.infradead.org > --- > net/rxrpc/input.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c > index 030d64f282f3..fc0d404f3b91 100644 > --- a/net/rxrpc/input.c > +++ b/net/rxrpc/input.c > @@ -806,6 +806,10 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb) > rxrpc_complete_rtt_probe(call, skb->tstamp, acked_serial, ack_serial, > rxrpc_rtt_rx_ping_response); > break; > + case RXRPC_ACK_PING: > + if (acked_serial == 0) > + break; > + fallthrough; > case RXRPC_ACK_REQUESTED: > rxrpc_complete_rtt_probe(call, skb->tstamp, acked_serial, ack_serial, > rxrpc_rtt_rx_requested_ack);
David,
I do not believe the ack_reason matters within rxrpc_input_ack(). As long as the acked_serial is non-zero, rxrpc_complete_rtt_probe() can be called to attempt to compute an RTT. If there is an exact match for the acked_serial then an RTT can be computed and if acked_serial is later than the pending rtt probe, the probe can be abandoned with the following caveats.
1. Receiving an acked_serial that is later than the serial of the transmitted probe indicates that a packet transmitted after the probe was received first. Or that reordering of the transmitted packets occurred. Or that the probe was never received by the peer; or that the peer's response to the probe was lost in transit. 2. The serial number namespace is unsigned 32-bit shared across all of the call channels of the associated rx connection. As the serial numbers will wrap the use of after() within rxrpc_complete_rtt_probe to compare their values is questionable. If serial numbers will be compared in this manner then they need to be locally tracked and compared as unsigned 64-bit values where only the low 32-bits are transmitted on the wire and any wire serial number equal to zero is ignored.
Jeffrey Altman
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