netdev - Re: TSQ accounting skb->truesize degrades throughput for large packets

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Date:	Mon, 9 Sep 2013 22:41:20 +0100
From:	Zoltan Kiss <zoltan.kiss@...rix.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Wei Liu <wei.liu2@...rix.com>,
	Jonathan Davies <Jonathan.Davies@...citrix.com>,
	Ian Campbell <ian.campbell@...rix.com>,
	<netdev@...r.kernel.org>, <xen-devel@...ts.xenproject.org>
Subject: Re: TSQ accounting skb->truesize degrades throughput for large packets

On 07/09/13 18:21, Eric Dumazet wrote:
> On Fri, 2013-09-06 at 10:00 -0700, Eric Dumazet wrote:
>> On Fri, 2013-09-06 at 17:36 +0100, Zoltan Kiss wrote:
>>
>>> So I guess it would be good to revisit the default value of this
>>> setting.
>>
>> If ixgbe requires 3 TSO packets in TX ring to get line rate, you also
>> can tweak dev->gso_max_size from 65535 to 64000.
>
> Another idea would be to no longer use tcp_limit_output_bytes but
>
> max(sk_pacing_rate / 1000, 2*MSS)

I've tried this on a freshly updated upstream, and it solved my problem 
on ixgbe:

-               if (atomic_read(&sk->sk_wmem_alloc) >= 
sysctl_tcp_limit_output_bytes) {
+               if (atomic_read(&sk->sk_wmem_alloc) >= 
max(sk->sk_pacing_rate / 1000, 2 * mss_now) ){

Now I can get proper line rate. Btw. I've tried to decrease 
dev->gso_max_size to 60K or 32K, both was ineffective.

Regards,

Zoli
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