[mythtv-users] ivtv Maximum bitrate

James Crow crow.jamesm at gmail.com
Tue Jun 22 12:37:41 UTC 2010

On Mon, Jun 21, 2010 at 2:32 PM, James Crow <crow.jamesm at gmail.com> wrote:
> On Mon, Jun 21, 2010 at 1:27 PM, John Drescher <drescherjm at gmail.com> wrote:
>>> No this is a slave backend and the database is on the same computer as
>>> the master backend. This computer has two physical drives. Once for OS
>>> and one for recordings. It has two PCI cards. The PVR-500 and a
>>> currently unused Pinnacle 800i clear-QAM/analog tuner. I would guess
>>> the onboard sound and nic are also sharing the PCI bus. Even with
>>> those things the PCI bus should have more than enough bandwidth. The
>>> hard drive is a seagate 7200 RPM SATA. I think it is 400MB. Should be
>>> able to easily handle two PVR recordings.
>> Can you try disabling frequency scaling if that is enabled?
>> John
> I will try tonight.
> Thanks,
> James

So I forced the CPU to maximum frequency with:
echo performance > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
cat /proc/cpuinfo showed 2600.00 MHz which is the max for this CPU.

I then changed my recordingprofile for MPEG2 HW cards to 6000 avg and
8500 max. I started two recordings and waited a few minutes until
commercial flagging kicked in and then checked the system log. I saw
no errors from the ivtv driver.

I then increased the avg rate to 6500 to match what it had been
before. I still saw no errors in the system log.

At this point it definitely appears to be a problem with the system
scaling back the clock speed when not under load.

Next question is what is the best way to fix this? I would rather not
leave my system running at max speed all the time. This is a Mythbuntu
10.04 amd64 system. The available cpufreq governors are:

james at myth-fe-2:/sys/devices/system/cpu/cpu0/cpufreq$ cat
conservative ondemand userspace powersave performance

The system was running with the ondemand governor.

I tried setting the governor back to ondemand and the up_threshold to
20. This resulted in a CPU freq of 1000.00 MHz. Or the slowest this
CPU can clock. I may have to set the threshold all the way down to 10.

Any ideas welcome.


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