@@ -2372,6 +2372,15 @@ union bpf_attr {
* current value is ect (ECN capable). Works with IPv6 and IPv4.
* Return
* 1 if set, 0 if not set.
+ *
+ * int bpf_tcp_check_probe_timer(struct bpf_tcp_sock *tp, int when_us)
+ * Description
+ * Checks that there are no packets out and there is no pending
+ * timer. If both of these are true, it bounds when_us by
+ * TCP_TIMEOUT_MIN (2 jiffies) or TCP_RTO_MIN (200ms) and
+ * sets the probe timer.
+ * Return
+ * 0
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -2472,7 +2481,8 @@ union bpf_attr {
FN(sk_fullsock), \
FN(tcp_sock), \
FN(tcp_enter_cwr), \
- FN(skb_ecn_set_ce),
+ FN(skb_ecn_set_ce), \
+ FN(tcp_check_probe_timer),
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
@@ -5456,6 +5456,31 @@ static const struct bpf_func_proto bpf_skb_ecn_set_ce_proto = {
.ret_type = RET_INTEGER,
.arg1_type = ARG_PTR_TO_CTX,
};
+
+BPF_CALL_2(bpf_tcp_check_probe_timer, struct tcp_sock *, tp, u32, when_us)
+{
+ struct sock *sk = (struct sock *) tp;
+ unsigned long when = usecs_to_jiffies(when_us);
+
+ if (!tp->packets_out && !inet_csk(sk)->icsk_pending) {
+ if (when < TCP_TIMEOUT_MIN)
+ when = TCP_TIMEOUT_MIN;
+ else if (when > TCP_RTO_MIN)
+ when = TCP_RTO_MIN;
+
+ tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
+ when, TCP_RTO_MAX, NULL);
+ }
+ return 0;
+}
+
+static const struct bpf_func_proto bpf_tcp_check_probe_timer_proto = {
+ .func = bpf_tcp_check_probe_timer,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_TCP_SOCK,
+ .arg2_type = ARG_ANYTHING,
+};
#endif /* CONFIG_INET */
bool bpf_helper_changes_pkt_data(void *func)
@@ -5624,6 +5649,13 @@ cg_skb_func_proto(enum bpf_func_id func_id, struct bpf_prog *prog)
}
case BPF_FUNC_skb_ecn_set_ce:
return &bpf_skb_ecn_set_ce_proto;
+ case BPF_FUNC_tcp_check_probe_timer:
+ if (prog->expected_attach_type == BPF_CGROUP_INET_EGRESS) {
+ prog->enforce_expected_attach_type = 1;
+ return &bpf_tcp_check_probe_timer_proto;
+ } else {
+ return NULL;
+ }
#endif
default:
return sk_filter_func_proto(func_id, prog);
This patch adds a new bpf helper BPF_FUNC_tcp_check_probe_timer "int bpf_check_tcp_probe_timer(struct tcp_bpf_sock *tp, u32 when_us)". It is added to BPF_PROG_TYPE_CGROUP_SKB typed bpf_prog which currently can be attached to the ingress and egress path. To ensure it is only called from BPF_CGROUP_INET_EGRESS, the attr->expected_attach_type must be specified as BPF_CGROUP_INET_EGRESS during load time if the prog uses this new helper. The newly added prog->enforce_expected_attach_type bit will also be set if this new helper is used. This bit is for backward compatibility reason because currently prog->expected_attach_type has been ignored in BPF_PROG_TYPE_CGROUP_SKB. During attach time, prog->expected_attach_type is only enforced if the prog->enforce_expected_attach_type bit is set. i.e. prog->expected_attach_type is only enforced if this new helper is used by the prog. The function forces when_us to be at least TCP_TIMEOUT_MIN (currently 2 jiffies) and no more than TCP_RTO_MIN (currently 200ms). When using a bpf_prog to limit the egress bandwidth of a cgroup, it can happen that we drop a packet of a connection that has no packets out. In this case, the connection may not retry sending the packet until the probe timer fires. Since the default value of the probe timer is at least 200ms, this can introduce link underutiliation (i.e. the cgroup egress bandwidth being smaller than the specified rate) thus increased tail latency. This helper function allows for setting a smaller probe timer. Signed-off-by: Lawrence Brakmo <brakmo@fb.com> --- include/uapi/linux/bpf.h | 12 +++++++++++- net/core/filter.c | 32 ++++++++++++++++++++++++++++++++ 2 files changed, 43 insertions(+), 1 deletion(-)