Re: Event based scheduling and USB.

On 10/26/2010 12:57 PM, Alexander Motin wrote:
> Takanori Watanabe wrote:
>> I updated my FreeBSD tree on laptop, to the current
>> as of 18 Oct.2010, it works fine with CPU C3 state enabled,
>>
>> I think this is your achievement of event time scheduler,
>> thanks!

Ah, so mav_at_ implemented a tickless-scheduler? That is nice.

>> But when USB driver is enabled, the load average is considerablly 
>> high (0.6 to 1.0) if sysctl oid kern.eventtimer.periodic is set to 0.
>>  Then kern.eventtimer.periodic is set to 1, the load average goes
>> to 0 quickly as before, but almost never transit to C3.
>>
>> Is this behavior expected, or something wrong?

The USB controller often keeps the bus mastering bit set. This keeps the
system out of C3. The way to fix this is to implement global suspend.
Put a device in suspend mode and then turn off power to the USB port it
is on. Then the USB controller will stop polling the bus.

>> I noticed one of usb host controller device shares HPET irq.
>> When I implement interrupt filter in uhci driver, the load average
>> goes to 0 as before.
>>
>>
>> ====
>> % vmstat -i
>> interrupt                          total       rate
>> irq1: atkbd0                         398          2
>> irq9: acpi0                          408          2
>> irq12: psm0                            3          0
>> irq19: ehci1                          37          0
>> irq20: hpet0 uhci0                 35970        230
>> irq22: ehci0                           2          0
>> irq256: em0                            4          0
>> irq257: ahci0                       1692         10
>> Total                              38514        246
>> ===
> 
> I haven't noticed that issue and it is surely not expected for me. I
> will try to reproduce it.
> 
> Most likely you should be able to avoid interrupt sharing using some
> additional HPET options, described at hpet(4).

This seems silly. The whole point of APIC is to avoid clustering on a
single interrupt but the BIOS put the timer on the USB controller irq?

>> It's time to implement powertop for freebsd, isn't it?
> 
> Surely it is. I was even thinking about possibility to port one from
> OpenSolaris, but other work distracted me. You may take it, it you wish.

It seems worth doing the internals new, but maybe outputting information
in a compatible format for reporting tools.

-- 
Nate