<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman, new york, times, serif;font-size:12pt"><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;">limits come into picture only if the program itself tries to change them. does myth try to renice itself to higher priority? I don't think so.<br><br>mythfrontend running with realtime priority doesn't really matter because its just the display part. actual read from the driver and write to disk happens in backend.<br><br>Can you also try the other combo for raid0 that I mentioned to rule a faulty disk (rule both hde and hdg out)?<br><br>-devsk<br><br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;">----- Original Message ----<br>From: Listbox <listbox@hymerfania.com><br>To: Discussion about mythtv <mythtv-users@mythtv.org><br>Sent: Sunday, December 31, 2006 2:53:05 PM<br>Subject: Re:
[mythtv-users] Slow video on XFS raid 0, ok video on ext3 on single drive.<br><br><div>Thanks so much!<br>But regarding nice, In /etc/security/limits.conf , I set<br>@mythtv - nice -10<br>@mythtv - rtprio 50<br> <br>And the startup trace shows <br>"Using realtime priority."<br> <br>Do I still have to start mythfronend with nice?<br> <br>Listbox<br><br>________________________________<br><br>From: devsk [mailto:funtoos@yahoo.com] <br>Sent: Sunday, December 31, 2006 11:20 AM<br>To: Discussion about mythtv<br>Subject: Re: [mythtv-users] Slow video on XFS raid 0,ok video on ext3 on<br>single drive.<br><br><br>Here is what you need to try: Slowly up (negative higher, 'man renice') the<br>nice value of mythbackend when watching livetv. Stop doing that when the<br>artifacts go away. Record that value and put it in a boot script.<br><br>the reasoning: we did a lot of experiments to see how the I/O latency<br>changes with priority of the process. As we increased the
priority, the IO<br>latency went down but thruput (number of IOs per sec) also went down. This<br>meant that the kernel was making sure that the higher priority tasks got<br>their IO completed quickly but in smaller chunks. This effect is more<br>pronounced with RAID0 because your latency is the worst case latency of all<br>the drives in the raid. And a 'good citizen' nice value doesn't help<br>backend.<br><br>One more thing to try is to remake the raid on hde-hdf or hdf-hdg and see if<br>that helps (particularly, you have a lot of disks, so backing up and<br>remaking should be no problem). It is possible that one of hde or hdg is<br>dying and suffering huge latencies. Your PCI card could be a culprit too.<br><br>Regardless of whether the renice works or not, get yourself a better PCI<br>card and move to SATA if you've got the dough.<br><br>-devsk<br><br><br><br>----- Original Message ----<br>From: Listbox <listbox@hymerfania.com><br>To: Discussion about mythtv
<mythtv-users@mythtv.org><br>Sent: Saturday, December 30, 2006 11:04:07 PM<br>Subject: Re: [mythtv-users] Slow video on XFS raid 0, ok video on ext3 on<br>single drive.<br><br><br>The RAID devices are hde and hdg, the/ partition is hdc.... to me this looks<br>like all my physical drives give comparable throughput.<br><br>/dev/hda:<br>Timing cached reads: 1668 MB in 2.00 seconds = 834.10 MB/sec<br>Timing buffered disk reads: 88 MB in 3.05 seconds = 28.87 MB/sec<br><br>/dev/hdb:<br>Timing buffered disk reads: <br>/dev/hdc:<br>Timing cached reads: 1696 MB in 2.00 seconds = 847.36 MB/sec<br>Timing buffered disk reads: 88 MB in 3.05 seconds = 28.82 MB/sec<br><br>/dev/hde:<br>Timing cached reads: 1680 MB in 2.00 seconds = 838.49 MB/sec<br>Timing buffered disk reads: 168 MB in 3.03 seconds
= 55.46 MB/sec<br><br>/dev/hdf:<br>Timing cached reads: 1688 MB in 2.00 seconds = 843.57 MB/sec<br>Timing buffered disk reads: 164 MB in 3.00 seconds = 54.59 MB/sec<br><br>/dev/hdg:<br>Timing cached reads: 1696 MB in 2.00 seconds = 846.68 MB/sec<br>Timing buffered disk reads: 162 MB in 3.03 seconds = 53.45 MB/sec<br><br>So, given the same hardware throughput, I would expect better performance<br>with the XFS+RAID setup. This is not the case.<br>My adapter is a:<br>RAID bus controller: Silicon Image, Inc. PCI0680 Ultra ATA-133 Host<br>Controller (rev 02)<br>I also tried upping the PCI latency of the RAID card with <br> setpci -v -s 01:07.0 latency_timer=B0 # PCI0680 Ultra ATA-133 Host<br>But this had no effect. The DVB card has a latency of 32(decimal).<br><br>I just reformatted with ext3, and tried again,
and got the same degradation.<br>It's looking like the RAID is the problem, but I do not,NOT,NOT! want to<br>un-stripe the disks. <br><br>What else to try?<br><br>Listbox<br><br>-----Original Message-----<br>From: Andrew Lyon [mailto:andrew.lyon@gmail.com] <br>Sent: Saturday, December 30, 2006 11:31 AM<br>To: Discussion about mythtv<br>Subject: Re: [mythtv-users] Slow video on XFS raid 0,ok video on ext3 on<br>single drive.<br><br>On 12/30/06, Listbox <listbox@hymerfania.com> wrote:<br>> Hi folks!<br>><br>> I have two Seagate 160gb drives in a RAID 0 array on an SiI0680 PCI <br>> ATA raid controller. I formatted an XFS filesystem on a single <br>> partition, and set mythbackend to use it. My DVB card is a DviCO <br>> Fusion Gold 3,( Conexant CX23880).<br>><br>> When I watch live TV, I get terrible artifacts on digital TV, and slow <br>> frame rates on analog. When I reset mythbackend to use a ext3 <br>> partition on a single drive,
performance is acceptable.<br>><br>> I went to considerable trouble to get the RAID and XFS working on my <br>> Fedora<br>> 5 system, and it's pretty discouraging to see that it actually <br>> degrades instead of enhances performance. What is likely the problem? <br>> Is it the controller, the raid or the filesystem?<br>><br>> Thanks for any advice!<br>><br>> Listbox<br>><br>> _______________________________________________<br>> mythtv-users mailing list<br>> mythtv-users@mythtv.org<br>> <a target="_blank" href="http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users">http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users</a><br>><br><br>Please use hdparm -tT to benchmark the speed of your drives, and your raid<br>array, e.g.<br><br>hdparm -tT /dev/sda /dev/sdb /dev/sdc /dev/md0<br><br>You should do this when the system is idle, perhaps even in single user<br>mode.<br><br>That should shed some light on the
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