USB: OHCI: high softirq load

[Antoine Aubert]

Thanks Johan, you save my day.

Indeed, soft irq coming from ftdi_sio updates, with very high rate.
(dyndbg='file drivers/usb/* +p')

reducing latency timer = reducing sofirq.

Problem solved.

Antoine Aubert
a.aubert at overkiz.com

Le 16/01/2017 à 15:47, Johan Hovold a écrit :
> [ +CC: linux-usb ]
>
> On Mon, Jan 16, 2017 at 12:14:03PM +0100, Boris Brezillon wrote:
>> On Mon, 16 Jan 2017 11:54:23 +0100
>> Antoine Aubert <a.aubert at overkiz.com> wrote:
>>
>>> Also, I made a big misunderstanding
>>>
>>> With EHCI + OHCI = high level of softirq (USB2.0)
>> Well, the number of irqs and softirqs are likely to be related (you
>> usually trigger a softirq after you received an hardirq).
>>
>>> OHCI only = normal level
>> What about EHCI only? And what happens if you only plug 1 device?
>> Please share the content of /proc/interrupts (and everything you think
>> is relevant) for each of these cases.
>>
>>> Le 16/01/2017 à 11:31, Antoine Aubert a écrit :
>>>> Thx for your answer Boris
>>>>
>>>> Le 16/01/2017 à 10:02, Boris Brezillon a écrit :  
>>>>> Hi Antoine,
>>>>>
>>>>> On Mon, 16 Jan 2017 08:45:58 +0100
>>>>> Antoine Aubert <a.aubert at overkiz.com> wrote:
>>>>>  
>>>>>> Hi,
>>>>>>
>>>>>> Im working on a AT91SAM9G25cu board
>>>>>> (arch/arm/boot/dts/at91-kizboxmini.dts). We use linux-4.1.31, and when
>>>>>> OHCI is enabled, I got some wired effects.  
>>>>> Can you test on a more recent kernel (4.9 or 4.10-rc4)?  
>>>> I'll give a try, just need little time ;)  
>>>>>> eg with 3 FTDI pluged, interrupts: more than 3.5k/s, cpu softirq > 24%,
>>>>>> loadavg > 0.5  
>>>>> Can you check which interrupt is triggered (cat /proc/interrupts),  
>>>> cat /proc/interrupts
>>>>            CPU0      
>>>>  16:       2286  atmel-aic   1 Level     pmc, at91_tick, at91_rtc, ttyS0
>>>>  17:          0       PMC  17 Level     main_rc_osc
>>>>  18:          0       PMC   0 Level     main_osc
>>>>  19:          0       PMC  16 Level     mainck
>>>>  20:          0       PMC   1 Level     clk-plla
>>>>  21:          0       PMC   6 Level     clk-utmi
>>>>  22:          0       PMC   3 Level     clk-master
>>>>  23:     945527  atmel-aic  17 Level     tc_clkevt
>>>>  24:      21815  atmel-aic  20 Level     at_hdmac
>>>>  25:          0  atmel-aic  21 Level     at_hdmac
>>>>  30:     120299  atmel-aic  24 Level     eth0
>>>>  31:   22783651  atmel-aic  22 Level     ehci_hcd:usb1, ohci_hcd:usb2
>>>>  99:          0      GPIO  16 Edge      PB_RST
>>>> 100:          0      GPIO  17 Edge      PB_PROG
>>>> Err:          0
> Note that the ftdi driver uses a low-latency setting by default which
> implies that the device sends a status update every millisecond. Hence,
> the 1k interrupts per second (per device) while the port is open is
> expected.
>
> You can disable the low-latency behaviour using setserial:
>
> 	setserial /dev/ttyUSB0 ^low_latency
>
> and see the number of interrupts drop to 1/16th. This can then be
> reduced further by changing the latency_timer from its
> (non-low-latency) default of 16 ms, for example:
>
> 	echo 64 >/sys/bus/usb-serial/devices/ttyUSB0/latency_timer
>
> Johan