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processor rqs for 2 dvb-t
http://forum.linhes.org/viewtopic.php?f=6&t=6290		 Page 1 of 1
Author:  declanh [ Mon Oct 03, 2005 3:13 pm ]
Post subject:  processor rqs for 2 dvb-t
ive build a knoppmyth box based on the following

asrock mini atx mobo
althon 1.4ghz
maxtor 120gb drive
wintv nova t (pci) tuner
radeon 7000 agp
creative cdrw

after alot of work ive mostly got things working but was wondering what the cpu rqs are for 2 dvb cards are - would the above cpu be enough.

Im thinking that since dvb streams from these cards are already encoded i can get away with less cpu - is this reasoning flawed ?

anyone else got a similar setup ?
Author:  tjc [ Mon Oct 03, 2005 7:47 pm ]
Post subject: 
Using the old system which was an Athlon XP 2500+ recording via a PVR-250, the % CPU usage was in the single digits. Watching live (record and playback at the same time) I never saw % CPU used go over 15%. I'd guess that you've got enough headroom for a second card, but why not measure on your own systyem?

Fire up an SSH session from another box, run top then start watching live TV. Monitor the output of top to see what your % Idle is. If the number is over 50% and your HD DMA is working then you're in good shape.
Author:  Greg Frost [ Mon Oct 03, 2005 10:32 pm ]
Post subject: 
I doubt he'd get over 50% idle. I get around 35% idle with an XP1700 processor watching standard def DVB (720x576 in PAL land). This is using the i686 compiled myth modules and the nvidia driver. perhaps tjc's PVR was capturing at lower resolution.
Author:  declanh [ Tue Oct 04, 2005 5:00 am ]
Post subject: 
watching livetv obviously is a burden as its recording and playing at the same time

so the scenarios with two tuners That i see are

Code:
Scenario,Tuner1,Tuner2,Watching Recorded Prog
1,Recording,Recording,Watching, 18
2,Live,Recording,Notwatching, 17
3,Recording,Live,Notwatching, 17
4,Recording,Recording,Notwatching, 14
5,Idle,Recording,Watching, 11
6,Recording,Idle,Watching, 11
7,Live,Idle,Notwatching, 10
8,Idle,Live,Notwatching, 10
9,Idle,Recording,Notwatching, 7
10,Recording,Idle,Notwatching, 7
11,Idle,Idle,Watching, 4
12,Idle,Idle,Notwatching, 0

Sorry i cant seem to get this to line up as i dont seem to be able to find a monospaced font option in the forum.
Scenario 1 is clearly the highest usage rqs for cpu.

With only one tuner the highest load possible is scenario 5 and i reckon this takes about 60% of my cpu... the question is will the extra DMA and overhead of writing two recorded streams mean that scenario

The weightings i placed on each operation in the table above were based on gut feeling and generated by the following perl script...



Code:
my %tunerstates = (Live=>10, Recording=>7, Idle=>0);
my %prerecorded = (Watching=>4, Notwatching=>0);

foreach $tuner1  (sort keys %tunerstates)
 {
 foreach $tuner2  (sort keys %tunerstates)
  {
   foreach $watching  (sort keys %prerecorded)
    {
     next if ($tuner1 eq "Live" && $tuner2 eq "Live");
     next if (($tuner1 eq "Live" || $tuner2 eq "Live") && ($watching eq "Watching"));
     $res {"$tuner1,$tuner2,$watching"} =
     $tunerstates{$tuner1}+$tunerstates{$tuner2}+$prerecorded{$watching};
    }
  }
 }
print "Scenario,Tuner1,Tuner2,Watching Recorded Prog\n";
foreach $x ( sort {$res{$b}<=>$res{$a}} keys %res)
{ print ++$line.",$x, $res{$x}\n"; }
Author:  tjc [ Tue Oct 04, 2005 12:46 pm ]
Post subject: 
That's why I asked foks with experience decodiing DVB what it took. ;-) Most of my experience is with NTSC at 480x480.

However recording a preencoded stream liike you get from a PVR, ATSC capture, or DVB capture card is not very demanding unless the drivers are a steaming heap of fish guts. All that'sinvolved is shuffling data to the disk which takes maybe 1/20th of the disks bandwidth (I've provided the calculations and measurements elsewhere around here), and even a slow CPU is capable of driving a disk at 100%. During my HDTV experiments the CPU overhead for recording was a drop in the bucket compared to the decoding.
Author:  declanh [ Sun Dec 04, 2005 6:15 pm ]
Post subject: 
Ive since bought a second DVB card Nova-t pci card and can report from experience

recording DVB on one card and Watching Livetv on the other loads my 1.4G Athlon at 48% so it looks like i have enought grunt to run with two cards.
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