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SVN multi-threading

 

 

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tom at redpepperracing

Feb 16, 2008, 11:27 AM

Post #1 of 4 (697 views)
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SVN multi-threading

I've seen that there have been some updates to trunk to allow
multi-threaded decoding of streams, and in the video profiles screen
there is a new 'max cpus' setting. However, that setting doesn't seem to
be doing anything, or even being saved, I can't find any evidence in the
settings table that it is stored there, and if I change it to '2', when
I play a stream it says 'Using 1 CPUs for decoding', and then I go back
into the video profile and it is set to 1 again. Also, does it only work
for h264 encoded streams, or will it help with MPEG2 as well?

I only ask because I am seeing more CPU usage on playback now than I was
a few weeks ago.

Tom

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ylee at pobox

Feb 16, 2008, 4:29 PM

Post #2 of 4 (640 views)
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Re: SVN multi-threading [In reply to]

Tom Lichti <tom[at]redpepperracing.com> says:
> I've seen that there have been some updates to trunk to allow
> multi-threaded decoding of streams, and in the video profiles screen
> there is a new 'max cpus' setting. However, that setting doesn't
> seem to be doing anything, or even being saved, I can't find any
> evidence in the settings table that it is stored there, and if I
> change it to '2', when I play a stream it says 'Using 1 CPUs for
> decoding', and then I go back into the video profile and it is set
> to 1 again.

I noticed the same thing. It seems that the individual entries in a
playback profile only save the Max CPUs setting when created;
subsequent edits don't change the number. Try deleting, then
recreating, an entry.

> Also, does it only work for h264 encoded streams, or will it help
> with MPEG2 as well?
>
> I only ask because I am seeing more CPU usage on playback now than I
> was a few weeks ago.

Sounds like what I noticed with my single-core Pentium 4 frontend. I
thought that, since the CPU is Hyperthreaded and thus emulates two
physical cores, bumping the Max CPUs number up to 2 would be a good
thing. Not so; CPU usage for mythfrontend running 1080i Bob playback
went from 50-70% to 100%+. So back to 1 I go.

--
Frontend: P4 3.0GHz, 1.5TB software RAID 5 array
Backend: Quad-core Xeon 1.6GHz, 6.6TB sw RAID 6
Video inputs: Four high-definition over FireWire/OTA
Accessories: 47" 1080p LCD, 5.1 digital, and MX-600
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billk at iinet

Feb 16, 2008, 7:36 PM

Post #3 of 4 (633 views)
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Re: SVN multi-threading [In reply to]

On Sat, 2008-02-16 at 16:29 -0800, Yeechang Lee wrote:
> Tom Lichti <tom[at]redpepperracing.com> says:
> > I've seen that there have been some updates to trunk to allow
> > multi-threaded decoding of streams, and in the video profiles screen
> > there is a new 'max cpus' setting. However, that setting doesn't
> >...
> >
> > I only ask because I am seeing more CPU usage on playback now than I
> > was a few weeks ago.
>
> Sounds like what I noticed with my single-core Pentium 4 frontend. I
> thought that, since the CPU is Hyperthreaded and thus emulates two
> physical cores, bumping the Max CPUs number up to 2 would be a good
> thing. Not so; CPU usage for mythfrontend running 1080i Bob playback
> went from 50-70% to 100%+. So back to 1 I go.

I was privy to some tests on high end PC hardware doing searches on huge
indexed flat file databases - enabling HT caused a quite marked
slowdown. The reason given was that HT uses unequal processing
pipelines - depending on what task was sent to which pipeline,
efficiency could (and did) suffer quite a lot. This could be the same
here.

Also, it might be worth checking that the SMT (HT scheduler...) option
is enabled in the kernel as well as the normal SMT option - I dont
remember when it appeared in the kernel, but it wasnt always there?

BillK




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tom at redpepperracing

Feb 17, 2008, 8:38 AM

Post #4 of 4 (622 views)
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Re: SVN multi-threading [In reply to]

Yeechang Lee wrote:
> Tom Lichti <tom[at]redpepperracing.com> says:
>
>> I've seen that there have been some updates to trunk to allow
>> multi-threaded decoding of streams, and in the video profiles screen
>> there is a new 'max cpus' setting. However, that setting doesn't
>> seem to be doing anything, or even being saved, I can't find any
>> evidence in the settings table that it is stored there, and if I
>> change it to '2', when I play a stream it says 'Using 1 CPUs for
>> decoding', and then I go back into the video profile and it is set
>> to 1 again.
>>
>
> I noticed the same thing. It seems that the individual entries in a
> playback profile only save the Max CPUs setting when created;
> subsequent edits don't change the number. Try deleting, then
> recreating, an entry.
>
I didn't delete them, but you pointed me in the right direction. For
some reason I had it stuck in my head to look in the settings table,
when really it's in the displayprofile table. I updated that to '2',
we'll see if it makes a difference.
>
>> Also, does it only work for h264 encoded streams, or will it help
>> with MPEG2 as well?
>>
>> I only ask because I am seeing more CPU usage on playback now than I
>> was a few weeks ago.
>>
>
> Sounds like what I noticed with my single-core Pentium 4 frontend. I
> thought that, since the CPU is Hyperthreaded and thus emulates two
> physical cores, bumping the Max CPUs number up to 2 would be a good
> thing. Not so; CPU usage for mythfrontend running 1080i Bob playback
> went from 50-70% to 100%+. So back to 1 I go.
>
I have a true dual core CPU, so it should help.

Tom

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