Re: [PATCH v3] irqchip/tango: Don't use incorrect irq_mask_ack callback

Marc Gonzalez
2017-09-18T08:51:11Z

On 21/08/2017 15:25, Marc Gonzalez wrote:

> Using separate mask and ack functions (i.e. my patch)
>
> # iperf3 -c 172.27.64.110 -t 20
> Connecting to host 172.27.64.110, port 5201
> [ 4] local 172.27.64.1 port 40868 connected to 172.27.64.110 port 5201
> [ ID] Interval Transfer Bandwidth Retr Cwnd
> [ 4] 0.00-1.00 sec 106 MBytes 888 Mbits/sec 18 324 KBytes
> [ 4] 1.00-2.00 sec 106 MBytes 885 Mbits/sec 0 361 KBytes
> [ 4] 2.00-3.00 sec 105 MBytes 883 Mbits/sec 4 279 KBytes
> [ 4] 3.00-4.00 sec 106 MBytes 890 Mbits/sec 0 300 KBytes
> [ 4] 4.00-5.00 sec 106 MBytes 887 Mbits/sec 0 310 KBytes
> [ 4] 5.00-6.00 sec 105 MBytes 883 Mbits/sec 0 315 KBytes
> [ 4] 6.00-7.00 sec 105 MBytes 885 Mbits/sec 0 321 KBytes
> [ 4] 7.00-8.00 sec 105 MBytes 880 Mbits/sec 0 325 KBytes
> [ 4] 8.00-9.00 sec 106 MBytes 888 Mbits/sec 0 329 KBytes
> [ 4] 9.00-10.00 sec 106 MBytes 886 Mbits/sec 0 335 KBytes
> [ 4] 10.00-11.00 sec 105 MBytes 885 Mbits/sec 0 351 KBytes
> [ 4] 11.00-12.00 sec 106 MBytes 887 Mbits/sec 1 276 KBytes
> [ 4] 12.00-13.00 sec 106 MBytes 885 Mbits/sec 0 321 KBytes
> [ 4] 13.00-14.00 sec 105 MBytes 883 Mbits/sec 0 349 KBytes
> [ 4] 14.00-15.00 sec 106 MBytes 890 Mbits/sec 0 366 KBytes
> [ 4] 15.00-16.00 sec 106 MBytes 888 Mbits/sec 2 286 KBytes
> [ 4] 16.00-17.00 sec 105 MBytes 884 Mbits/sec 0 303 KBytes
> [ 4] 17.00-18.00 sec 105 MBytes 883 Mbits/sec 0 311 KBytes
> [ 4] 18.00-19.00 sec 105 MBytes 880 Mbits/sec 0 315 KBytes
> [ 4] 19.00-20.00 sec 106 MBytes 890 Mbits/sec 0 321 KBytes
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval Transfer Bandwidth Retr
> [ 4] 0.00-20.00 sec 2.06 GBytes 885 Mbits/sec 25 sender
>
>
> Using combined mask and ack functions (i.e. Doug's patch)
>
> # iperf3 -c 172.27.64.110 -t 20
> Connecting to host 172.27.64.110, port 5201
> [ 4] local 172.27.64.1 port 41235 connected to 172.27.64.110 port 5201
> [ ID] Interval Transfer Bandwidth Retr Cwnd
> [ 4] 0.00-1.00 sec 107 MBytes 897 Mbits/sec 60 324 KBytes
> [ 4] 1.00-2.00 sec 107 MBytes 898 Mbits/sec 0 361 KBytes
> [ 4] 2.00-3.00 sec 107 MBytes 898 Mbits/sec 39 194 KBytes
> [ 4] 3.00-4.00 sec 107 MBytes 895 Mbits/sec 0 214 KBytes
> [ 4] 4.00-5.00 sec 107 MBytes 901 Mbits/sec 0 223 KBytes
> [ 4] 5.00-6.00 sec 108 MBytes 902 Mbits/sec 0 230 KBytes
> [ 4] 6.00-7.00 sec 107 MBytes 895 Mbits/sec 0 242 KBytes
> [ 4] 7.00-8.00 sec 107 MBytes 901 Mbits/sec 0 253 KBytes
> [ 4] 8.00-9.00 sec 107 MBytes 899 Mbits/sec 0 264 KBytes
> [ 4] 9.00-10.00 sec 108 MBytes 903 Mbits/sec 0 276 KBytes
> [ 4] 10.00-11.00 sec 108 MBytes 902 Mbits/sec 0 286 KBytes
> [ 4] 11.00-12.00 sec 107 MBytes 899 Mbits/sec 0 300 KBytes
> [ 4] 12.00-13.00 sec 107 MBytes 898 Mbits/sec 33 247 KBytes
> [ 4] 13.00-14.00 sec 107 MBytes 900 Mbits/sec 0 294 KBytes
> [ 4] 14.00-15.00 sec 107 MBytes 900 Mbits/sec 0 325 KBytes
> [ 4] 15.00-16.00 sec 107 MBytes 899 Mbits/sec 0 342 KBytes
> [ 4] 16.00-17.00 sec 107 MBytes 898 Mbits/sec 0 351 KBytes
> [ 4] 17.00-18.00 sec 108 MBytes 902 Mbits/sec 0 355 KBytes
> [ 4] 18.00-19.00 sec 107 MBytes 901 Mbits/sec 0 359 KBytes
> [ 4] 19.00-20.00 sec 108 MBytes 903 Mbits/sec 32 255 KBytes
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval Transfer Bandwidth Retr
> [ 4] 0.00-20.00 sec 2.09 GBytes 900 Mbits/sec 164 sender
>
>
> Ergo, it seems that the performance improvement of the combined
> implementation is approximately 1.5% for a load generating ~80k
> interrupts per second.

Hello irqchip maintainers,

As mentioned upthread, there is a bug in drivers/irqchip/irq-tango.c
caused by the unexpected implementation of irq_gc_mask_disable_reg_and_ack()

That bug can be fixed either by using an appropriate irq_mask_ack callback,
or by not defining an irq_mask_ack callback at all. The first option provides
~1.5% more throughput than the second, for a typical use-case.

Whichever option you favor, can we fix this bug in current and stable branches?
(The fix was submitted two months ago.)

Regards.