On 4 February 2015 at 22:11, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> I do not see how a TSO patch could hurt a flow not using TSO/GSO.
>
> This makes no sense.
Hmm..
@@ -2018,8 +2053,8 @@ 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_t(unsigned int, sysctl_tcp_limit_output_bytes,
- sk->sk_pacing_rate >> 10);
+ limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
+ limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
if (atomic_read(&sk->sk_wmem_alloc) > limit) {
set_bit(TSQ_THROTTLED, &tp->tsq_flags);
Doesn't this effectively invert how tcp_limit_output_bytes is used?
This would explain why raising the limit wasn't changing anything
anymore when you asked me do so. Only decreasing it yielded any
change.
I've added a printk to show up the new and old values. Excerpt from logs:
[ 114.782740] (4608 39126 131072 = 39126) vs (131072 39126 = 131072)
(2*truesize, pacing_rate, tcp_limit = limit) vs (tcp_limit, pacing_rate = limit)
Reverting this patch hunk alone fixes my TCP problem. Not that I'm
saying the old logic was correct (it seems it wasn't, a limit should
be applied as min(value, max_value), right?).
Anyway the change doesn't seem to be TSO-only oriented so it would
explain the "makes no sense".
Michał
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