Re: [PATCH net-next] net: stmmac: set total length of the packet to be transmitted in TDES3
From: Niklas Cassel
Date: Tue Apr 11 2017 - 05:10:16 EST
On 04/11/2017 10:48 AM, Joao Pinto wrote:
>
> Hi Niklas,
>
> Às 7:33 PM de 4/10/2017, Niklas Cassel escreveu:
>> From: Niklas Cassel <niklas.cassel@xxxxxxxx>
>>
>> Field FL/TPL in register TDES3 is not correctly set on GMAC4.
>> TX appears to be functional on GMAC 4.10a even if this field is not set,
>> however, to avoid relying on undefined behavior, set the length in TDES3.
>>
>> The field has a different meaning depending on if the TSE bit in TDES3
>> is set or not (TSO). However, regardless of the TSE bit, the field is
>> not optional. The field is already set correctly when the TSE bit is set.
>>
>> Since there is no limit for the number of descriptors that can be
>> used for a single packet, the field should be set to the sum of
>> the buffers contained in:
>> [<desc with First Descriptor bit set> ... <desc n> ...
>> <desc with Last Descriptor bit set>], which should be equal to skb->len.
>>
>> Signed-off-by: Niklas Cassel <niklas.cassel@xxxxxxxx>
>
> Sounds fine to me. Did you check for performance improvement? Thanks.
>
Hello Joao,
I could not see any difference with 1 TCP stream in iperf3
Without the patch:
# ./iperf3-armhf -c 192.168.0.1
Connecting to host 192.168.0.1, port 5201
[ 4] local 192.168.0.105 port 51878 connected to 192.168.0.1 port 5201
[ 23.486426] random: fast init done
[ ID] Interval Transfer Bandwidth Retr Cwnd
[ 4] 0.00-1.00 sec 61.7 MBytes 517 Mbits/sec 0 294 KBytes
[ 4] 1.00-2.00 sec 61.3 MBytes 515 Mbits/sec 0 294 KBytes
[ 26.043850] random: crng init done
[ 4] 2.00-3.00 sec 61.4 MBytes 515 Mbits/sec 0 294 KBytes
[ 4] 3.00-4.00 sec 61.0 MBytes 512 Mbits/sec 0 294 KBytes
[ 4] 4.00-5.00 sec 61.5 MBytes 516 Mbits/sec 0 294 KBytes
[ 4] 5.00-6.00 sec 61.2 MBytes 514 Mbits/sec 0 294 KBytes
[ 4] 6.00-7.00 sec 61.5 MBytes 516 Mbits/sec 0 294 KBytes
[ 4] 7.00-8.00 sec 61.4 MBytes 515 Mbits/sec 0 294 KBytes
[ 4] 8.00-9.00 sec 61.2 MBytes 514 Mbits/sec 0 294 KBytes
[ 4] 9.00-10.00 sec 61.3 MBytes 514 Mbits/sec 0 294 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 614 MBytes 515 Mbits/sec 0 sender
[ 4] 0.00-10.00 sec 613 MBytes 514 Mbits/sec receiver
With the patch:
# ./iperf3-armhf -c 192.168.0.1
Connecting to host 192.168.0.1, port 5201
[ 4] local 192.168.0.105 port 37696 connected to 192.168.0.1 port 5201
[ 85.266262] random: fast init done
[ ID] Interval Transfer Bandwidth Retr Cwnd
[ 4] 0.00-1.00 sec 62.1 MBytes 520 Mbits/sec 0 288 KBytes
[ 4] 1.00-2.00 sec 61.0 MBytes 512 Mbits/sec 0 288 KBytes
[ 87.782547] random: crng init done
[ 4] 2.00-3.00 sec 61.3 MBytes 515 Mbits/sec 0 300 KBytes
[ 4] 3.00-4.00 sec 61.1 MBytes 512 Mbits/sec 0 300 KBytes
[ 4] 4.00-5.00 sec 61.4 MBytes 515 Mbits/sec 0 300 KBytes
[ 4] 5.00-6.00 sec 61.1 MBytes 513 Mbits/sec 0 300 KBytes
[ 4] 6.00-7.00 sec 61.1 MBytes 513 Mbits/sec 0 300 KBytes
[ 4] 7.00-8.00 sec 61.6 MBytes 517 Mbits/sec 0 300 KBytes
[ 4] 8.00-9.00 sec 61.3 MBytes 515 Mbits/sec 0 300 KBytes
[ 4] 9.00-10.00 sec 61.6 MBytes 517 Mbits/sec 0 300 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 614 MBytes 515 Mbits/sec 0 sender
[ 4] 0.00-10.00 sec 613 MBytes 514 Mbits/sec receiver
Note that the results above are with TSO off.
With TSO on, I get 921 Mbps.
However, the patch should not affect the case where TSO is on.
Regards,
Niklas