netdev - Re: Throughput regression with `tcp: refine TSO autosizing`

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Message-ID: <CA+BoTQ=BDcQ779uKCuX+f40=4npXVF4MTQnpjKimNYAxPsxBoQ@mail.gmail.com>
Date:	Wed, 4 Feb 2015 13:22:23 +0100
From:	Michal Kazior <michal.kazior@...to.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	linux-wireless <linux-wireless@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	eyalpe@....mellanox.co.il
Subject: Re: Throughput regression with `tcp: refine TSO autosizing`

On 4 February 2015 at 12:57, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Wed, 2015-02-04 at 12:35 +0100, Michal Kazior wrote:
>
>> > (Or maybe wifi drivers should start to use skb->xmit_more as a signal to end aggregation)
>>
>> This could work if your firmware/device supports this kind of thing.
>> To my understanding ath10k firmware doesn't.
>
> This is a pure software signal. You do not need firmware support.
>
> Idea is the following :
>
> Your driver gets a train of messages, coming from upper layers (TCP, IP,
> qdisc)
>
> It can know that a packet is not the last one, by looking at
> skb->xmit_more.
>
> Basically, aggregation logic could use this signal as a very clear
> indicator you got the end of a train -> force the xmit right now.

There's no way to tell ath10k firmware: "xmit right now". The firmware
does all tx aggregation logic by itself. Host driver just submits a
frame and hopes it'll get out soon. It's not even a tx-ring you'd
expect. Each frame has a host assigned id which firmware then uses in
tx completion.


> To disable gso you would have to use :
>
> ethtool -K wlan1 gso off

Oh, thanks! This works. However I can't turn it on:

; ethtool -K wlan1 gso on
Could not change any device features

..so I guess it makes no sense to re-run tests because:

; ethtool -k wlan1 | grep generic
        tx-checksum-ip-generic: on [fixed]
generic-segmentation-offload: off [requested on]
generic-receive-offload: on

And this seems to never change.


Michał
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