On 4/17/24 6:11 AM, Eric Dumazet wrote:
On Wed, Apr 17, 2024 at 2:46 PM Philo Lu <lulie@xxxxxxxxxxxxxxxxx> wrote:
Add TCP_SKB_CB(skb)->sacked as the 4th arg of sockops passed to bpf
program. Then we can get the retransmission efficiency by counting skbs
w/ and w/o TCPCB_EVER_RETRANS mark. And for this purpose, sacked
updating is moved after the BPF_SOCK_OPS_RETRANS_CB hook.
Signed-off-by: Philo Lu <lulie@xxxxxxxxxxxxxxxxx>
This might be a naive question, but how the bpf program know what is the meaning
of each bit ?
Are they exposed already, and how future changes in TCP stack could
break old bpf programs ?
#define TCPCB_SACKED_ACKED 0x01 /* SKB ACK'd by a SACK block */
#define TCPCB_SACKED_RETRANS 0x02 /* SKB retransmitted */
#define TCPCB_LOST 0x04 /* SKB is lost */
#define TCPCB_TAGBITS 0x07 /* All tag bits */
#define TCPCB_REPAIRED 0x10 /* SKB repaired (no skb_mstamp_ns) */
#define TCPCB_EVER_RETRANS 0x80 /* Ever retransmitted frame */
#define TCPCB_RETRANS (TCPCB_SACKED_RETRANS|TCPCB_EVER_RETRANS| \
TCPCB_REPAIRED)
I think it is the best to use the trace_tcp_retransmit_skb() tracepoint instead.
iiuc the use case, moving the "TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;"
after the tracepoint should have similar effect.
If the TCPCB_* is moved to a enum, it will be included in the "vmlinux.h" that
the bpf prog can use and no need to expose them in uapi.
