Re: Throughput regression with `tcp: refine TSO autosizing`
flat view
From: Eric Dumazet <hidden>
Date: 2015-02-09 15:11:33
Also in:
linux-wireless
Possibly related (same subject, not in this thread)
- 2015-02-24 · Re: Throughput regression with `tcp: refine TSO autosizing` · Johannes Berg <johannes@sipsolutions.net>
- 2015-02-24 · Re: Throughput regression with `tcp: refine TSO autosizing` · Johannes Berg <johannes@sipsolutions.net>
- 2015-02-24 · Re: Throughput regression with `tcp: refine TSO autosizing` · Johannes Berg <hidden>
- 2015-02-12 · Re: Throughput regression with `tcp: refine TSO autosizing` · Dave Taht <hidden>
- 2015-02-12 · Re: Throughput regression with `tcp: refine TSO autosizing` · Michal Kazior <hidden>
On Mon, 2015-02-09 at 14:47 +0100, Michal Kazior wrote:
quoted hunk ↗ jump to hunk
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 65caf8b..5e249bf 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c@@ -1996,6 +1996,7 @@ static bool tcp_write_xmit(struct sock *sk,unsigned int mss_now, int nonagle, max_segs = tcp_tso_autosize(sk, mss_now); while ((skb = tcp_send_head(sk))) { unsigned int limit; + unsigned int amount; tso_segs = tcp_init_tso_segs(sk, skb, mss_now); BUG_ON(!tso_segs);@@ -2053,7 +2054,9 @@ static bool tcp_write_xmit(struct sock *sk,unsigned int mss_now, int nonagle, * of queued bytes to ensure line rate. * One example is wifi aggregation (802.11 AMPDU) */ - limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10); + amount = sk->sk_tx_completion_delay_us * + (sk->sk_pacing_rate >> 10); + limit = max(2 * skb->truesize, amount >> 10); limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes); if (atomic_read(&sk->sk_wmem_alloc) > limit) {
This is not what I suggested. If you test this on any other network device, you'll have sk->sk_tx_completion_delay_us == 0 amount = 0 * (sk->sk_pacing_rate >> 10); --> 0 limit = max(2 * skb->truesize, amount >> 10); --> 2 * skb->truesize So non TSO/GSO NIC will not be able to queue more than 2 MSS (one MSS per skb) Then if you store only the last tx completion, you have the possibility of having a last packet of a train (say a retransmit) to make it very low. Ideally the formula would be in TCP something very fast to compute : amount = (sk->sk_pacing_rate >> 10) + sk->tx_completion_delay_cushion; limit = max(2 * skb->truesize, amount); limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes); So a 'problematic' driver would have to do the math (64 bit maths) like this : sk->tx_completion_delay_cushion = ewma_tx_delay * sk->sk_pacing_rate;