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Lengthy delay watching recordings

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Rich.West at wesmo

May 22, 2012, 11:19 AM

Post #1 of 11 (825 views)
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Lengthy delay watching recordings

I noticed that going to 0.25 about a month back that the delay to start
playing an HD video had increased substantially and was curious as to
what might be the cause.

As I looked further, I realized that it is with all video, but HD
content appears to be the most obvious offender. It can take up to 31
seconds from the moment the user selects the video to play before it
actually starts playing.

My backend system is well used, but from the graphs I have, it's not
hurting with CPU or memory. Network to the frontends are all hardwired
(backend is gig, frontends are 100 meg). From a utilization
perspective, the drives on the backend server are always hovering at
around 85% utilization, which is good, and the general I/O on the drives
is not such that it would cause a negative impact.

I am using commercial detection, so I do suspect that there is some form
of buffering going on, but for 31 seconds? No network errors on the
switch or the interface for the frontend or the backend. CPU
utilization on the frontend is low.. basically idle.

I'm just wondering if there is a particular place within MythTV to look
(for example, I recently found that it was recommended that "quick
tuning" should be enabled for the hdhomerun)..

Thanks!
-Rich
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Jim at Morton

May 22, 2012, 11:32 AM

Post #2 of 11 (805 views)
Permalink

Re: Lengthy delay watching recordings [In reply to]

On 5/22/2012 2:19 PM, Rich West wrote:
> I noticed that going to 0.25 about a month back that the delay to start
> playing an HD video had increased substantially and was curious as to
> what might be the cause.
>
> As I looked further, I realized that it is with all video, but HD
> content appears to be the most obvious offender. It can take up to 31
> seconds from the moment the user selects the video to play before it
> actually starts playing.
>
> My backend system is well used, but from the graphs I have, it's not
> hurting with CPU or memory. Network to the frontends are all hardwired
> (backend is gig, frontends are 100 meg). From a utilization
> perspective, the drives on the backend server are always hovering at
> around 85% utilization, which is good, and the general I/O on the drives
> is not such that it would cause a negative impact.
>
> I am using commercial detection, so I do suspect that there is some form
> of buffering going on, but for 31 seconds? No network errors on the
> switch or the interface for the frontend or the backend. CPU
> utilization on the frontend is low.. basically idle.
>
> I'm just wondering if there is a particular place within MythTV to look
> (for example, I recently found that it was recommended that "quick
> tuning" should be enabled for the hdhomerun)..
>
Um, check the logs?

--
_________________________________________________________

Jim Morton

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Rich.West at wesmo

May 22, 2012, 12:32 PM

Post #3 of 11 (808 views)
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Re: Lengthy delay watching recordings [In reply to]

On 05/22/2012 02:32 PM, Jim Morton wrote:
> On 5/22/2012 2:19 PM, Rich West wrote:
>> I noticed that going to 0.25 about a month back that the delay to start
>> playing an HD video had increased substantially and was curious as to
>> what might be the cause.
>>
>> As I looked further, I realized that it is with all video, but HD
>> content appears to be the most obvious offender. It can take up to 31
>> seconds from the moment the user selects the video to play before it
>> actually starts playing. ...
>>
> Um, check the logs?

lol. Nothing really obvious in there, either.. no major errors.
Granted, mythbackend logs like a screaming siren, but I will look again.

-Rich

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mtdean at thirdcontact

May 22, 2012, 12:46 PM

Post #4 of 11 (802 views)
Permalink

Re: Lengthy delay watching recordings [In reply to]

On 05/22/2012 02:19 PM, Rich West wrote:
> I noticed that going to 0.25 about a month back that the delay to start
> playing an HD video had increased substantially and was curious as to
> what might be the cause.
>
> As I looked further, I realized that it is with all video, but HD
> content appears to be the most obvious offender. It can take up to 31
> seconds from the moment the user selects the video to play before it
> actually starts playing.
>
> My backend system is well used, but from the graphs I have, it's not
> hurting with CPU or memory. Network to the frontends are all hardwired
> (backend is gig, frontends are 100 meg). From a utilization
> perspective, the drives on the backend server are always hovering at
> around 85% utilization, which is good, and the general I/O on the drives
> is not such that it would cause a negative impact.
>
> I am using commercial detection, so I do suspect that there is some form
> of buffering going on, but for 31 seconds? No network errors on the
> switch or the interface for the frontend or the backend. CPU
> utilization on the frontend is low.. basically idle.
>
> I'm just wondering if there is a particular place within MythTV to look
> (for example, I recently found that it was recommended that "quick
> tuning" should be enabled for the hdhomerun)..
>

/me guesses you have MySQL data on a file system with barriers enabled.

Mike
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josu.lazkano at gmail

May 22, 2012, 1:51 PM

Post #5 of 11 (805 views)
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Re: Lengthy delay watching recordings [In reply to]

2012/5/22 Michael T. Dean <mtdean [at] thirdcontact>

> On 05/22/2012 02:19 PM, Rich West wrote:
>
>> I noticed that going to 0.25 about a month back that the delay to start
>> playing an HD video had increased substantially and was curious as to
>> what might be the cause.
>>
>> As I looked further, I realized that it is with all video, but HD
>> content appears to be the most obvious offender. It can take up to 31
>> seconds from the moment the user selects the video to play before it
>> actually starts playing.
>>
>> My backend system is well used, but from the graphs I have, it's not
>> hurting with CPU or memory. Network to the frontends are all hardwired
>> (backend is gig, frontends are 100 meg). From a utilization
>> perspective, the drives on the backend server are always hovering at
>> around 85% utilization, which is good, and the general I/O on the drives
>> is not such that it would cause a negative impact.
>>
>> I am using commercial detection, so I do suspect that there is some form
>> of buffering going on, but for 31 seconds? No network errors on the
>> switch or the interface for the frontend or the backend. CPU
>> utilization on the frontend is low.. basically idle.
>>
>> I'm just wondering if there is a particular place within MythTV to look
>> (for example, I recently found that it was recommended that "quick
>> tuning" should be enabled for the hdhomerun)..
>>
>>
> /me guesses you have MySQL data on a file system with barriers enabled.
>
> Mike
>
> ______________________________**_________________
> mythtv-users mailing list
> mythtv-users [at] mythtv
> http://www.mythtv.org/mailman/**listinfo/mythtv-users<http://www.mythtv.org/mailman/listinfo/mythtv-users>
>

Hello, I have same problem on 0.25. My system is a combined frontend
backend.

MySQL data is on the same partition as the system:

/dev/sda1 on / type ext4
(rw,relatime,errors=remount-ro,user_xattr,barrier=1,data=ordered)

How could I change the barrier on my partition?

Kind regards.

--
Josu Lazkano

mtdean at thirdcontact

May 22, 2012, 1:55 PM

Post #6 of 11 (805 views)
Permalink

Re: Lengthy delay watching recordings [In reply to]

On 05/22/2012 04:51 PM, Josu Lazkano wrote:
>
> Hello, I have same problem on 0.25. My system is a combined frontend
> backend.
>
> MySQL data is on the same partition as the system:
>
> /dev/sda1 on / type ext4
> (rw,relatime,errors=remount-ro,user_xattr,barrier=1,data=ordered)
>
> How could I change the barrier on my partition?

You should mention which distro you're using and then people will be
able to provide appropriate directions for your distro's configuration
tools.

That said, I'm not saying you /should/ disable barriers. I think it's
well worth testing with barriers disabled, but you will need to
determine whether you want performance at the expense of safety by
disabling barriers.

Mike
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josu.lazkano at gmail

May 22, 2012, 2:20 PM

Post #7 of 11 (793 views)
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Re: Lengthy delay watching recordings [In reply to]

2012/5/22 Michael T. Dean <mtdean [at] thirdcontact>

> On 05/22/2012 04:51 PM, Josu Lazkano wrote:
>
>>
>> Hello, I have same problem on 0.25. My system is a combined frontend
>> backend.
>>
>> MySQL data is on the same partition as the system:
>>
>> /dev/sda1 on / type ext4 (rw,relatime,errors=remount-**
>> ro,user_xattr,barrier=1,data=**ordered)
>>
>> How could I change the barrier on my partition?
>>
>
> You should mention which distro you're using and then people will be able
> to provide appropriate directions for your distro's configuration tools.
>
> That said, I'm not saying you /should/ disable barriers. I think it's
> well worth testing with barriers disabled, but you will need to determine
> whether you want performance at the expense of safety by disabling barriers.
>
>
> Mike
> ______________________________**_________________
> mythtv-users mailing list
> mythtv-users [at] mythtv
> http://www.mythtv.org/mailman/**listinfo/mythtv-users<http://www.mythtv.org/mailman/listinfo/mythtv-users>
>

Thanks Michael,

I am using Debian, on the stable version (0.24) the fs was EXT3 and there
was no long time to start the recording. Now with testing version (0.25)
the fs is EXT4 and it takes long.

I just read that it will be dangerous to disable the barriers, so I will
read more.

Thanks and best regards.

--
Josu Lazkano

mtdean at thirdcontact

May 22, 2012, 3:23 PM

Post #8 of 11 (797 views)
Permalink

Re: Lengthy delay watching recordings [In reply to]

On 05/22/2012 05:20 PM, Josu Lazkano wrote:
> 2012/5/22 Michael T. Dean
>
>> On 05/22/2012 04:51 PM, Josu Lazkano wrote:
>>
>>> Hello, I have same problem on 0.25. My system is a combined frontend
>>> backend.
>>>
>>> MySQL data is on the same partition as the system:
>>>
>>> /dev/sda1 on / type ext4 (rw,relatime,errors=remount-**
>>> ro,user_xattr,barrier=1,data=**ordered)
>>>
>>> How could I change the barrier on my partition?
>>>
>> You should mention which distro you're using and then people will be able
>> to provide appropriate directions for your distro's configuration tools.
>>
>> That said, I'm not saying you /should/ disable barriers. I think it's
>> well worth testing with barriers disabled, but you will need to determine
>> whether you want performance at the expense of safety by disabling barriers.
> Thanks Michael,
>
> I am using Debian, on the stable version (0.24) the fs was EXT3 and there
> was no long time to start the recording. Now with testing version (0.25)
> the fs is EXT4 and it takes long.
>
> I just read that it will be dangerous to disable the barriers, so I will
> read more.
>
> Thanks and best regards.

FWIW, here's the "generic" way of disabling barriers:

http://www.gossamer-threads.com/lists/mythtv/users/414769#414769

(so, for example, adding that as an option in /etc/fstab), but not sure
if anything in the distro will overwrite your changes or whatever. The
thread also has some discussion and information.

Mike
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snharris99 at live

May 22, 2012, 4:25 PM

Post #9 of 11 (790 views)
Permalink

Re: Lengthy delay watching recordings [In reply to]

>I noticed that going to 0.25 about a month back that the delay to start
>playing an HD video had increased substantially and was curious as to
>what might be the cause.

>As I looked further, I realized that it is with all video, but HD
>content appears to be the most obvious offender. It can take up to 31
>seconds from the moment the user selects the video to play before it
>actually starts playing.

>My backend system is well used, but from the graphs I have, it's not
>hurting with CPU or memory. Network to the frontends are all hardwired
>(backend is gig, frontends are 100 meg). From a utilization
>perspective, the drives on the backend server are always hovering at
>around 85% utilization, which is good, and the general I/O on the drives
>is not such that it would cause a negative impact.

>I am using commercial detection, so I do suspect that there is some form
>of buffering going on, but for 31 seconds? No network errors on the
>switch or the interface for the frontend or the backend. CPU
>utilization on the frontend is low.. basically idle.

>I'm just wondering if there is a particular place within MythTV to look
>(for example, I recently found that it was recommended that "quick
>tuning" should be enabled for the hdhomerun)..

>Thanks!
>-Rich

FWIW, ext4 / barriers discussion aside, my systems have started exhibiting
the same behavior. The last time this happened, it turned out to be the
NVidia 295 drivers (some major segfault issue) and rolling back to 280.13
fixed it right up. At some point, NVidia fixed the isssues in the 295
driver line, but I'm wondering if it's back (this latest round of "startup
delays" seems to have timed almost perfectly with the 295.53 driver release
from x-swat). I haven't yet, but I intend on rolling back again to see if
it resolves the issue.

Also, I have noticed that usually I have to restart the frontend with my
remote button / script and then the same video usually loads right up.
That, along with random, mysterious frontend crashes (like simply navigating
menus) are almost identical symptoms of the last time NVidia drivers were
killing me.

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Jens.Peder.Terjesen at devoteam

May 23, 2012, 9:05 AM

Post #10 of 11 (771 views)
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Re: Lengthy delay watching recordings [In reply to]

-----Original Message-----
On 22. mai 2012 9:46 Michael T. Dean wrote:

On 05/22/2012 02:19 PM, Rich West wrote:
> I noticed that going to 0.25 about a month back that the delay to
> start playing an HD video had increased substantially and was curious
> as to what might be the cause.
>
> As I looked further, I realized that it is with all video, but HD
> content appears to be the most obvious offender. It can take up to 31
> seconds from the moment the user selects the video to play before it
> actually starts playing.
>
> My backend system is well used, but from the graphs I have, it's not
> hurting with CPU or memory. Network to the frontends are all
> hardwired (backend is gig, frontends are 100 meg). From a utilization
> perspective, the drives on the backend server are always hovering at
> around 85% utilization, which is good, and the general I/O on the
> drives is not such that it would cause a negative impact.
>
> I am using commercial detection, so I do suspect that there is some
> form of buffering going on, but for 31 seconds? No network errors on the
> switch or the interface for the frontend or the backend. CPU
> utilization on the frontend is low.. basically idle.
>
> I'm just wondering if there is a particular place within MythTV to
> look (for example, I recently found that it was recommended that
> "quick tuning" should be enabled for the hdhomerun)..
>

/me guesses you have MySQL data on a file system with barriers enabled.

Mike
-----Original Message-----

I don't have this problem but get irregular periods of freezes on the frontend.
I am not so sure that barriers enabled or not is the cause of this, based on the following observations.

On my combined FE/BE I was running 0.24 until the beginning of December 2011 without any problems like this.
I then switched to the development 0.25-pre version because of frequent tuning problems, and updated regularly until 0.25 was released.

Up until some time early in 2012, probably around February/March there were still no problems with freezing.
After this point in time I started to get 30-120 second freezes on the frontend. After some time I found that the mysqld process was using near 100% of one core for very long periods, and the freezes coincided with this.

After getting an UPS working for the FE/BE I disabled barriers on the OS/database partition which is EXT4.
The rescheduling time went down from about 25-30 seconds to about 15 seconds, but the freezes where still the same.

Using SHOW PROCESSLIST; in mysql showed that insertions and modifications of the program table had a status of LOCKED for long periods of time while the mysqld CPU load was at near 100%.
http://www.gossamer-threads.com/lists/mythtv/users/510064#510064

Being a little desperate I deleted all recording rules, and the freezes and high CPU load where all gone.
Well a PVR without any recording rules isn't of much value, so after monitoring for a while I started adding recording rules back. With just a few recording rules the system worked fine. Now when I am more or less back at the same number of recording rules I see freezes lasting from 10-25 seconds.

Jens

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Rich.West at wesmo

May 23, 2012, 1:53 PM

Post #11 of 11 (772 views)
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Re: Lengthy delay watching recordings [In reply to]

On 05/22/2012 03:46 PM, Michael T. Dean wrote:
> On 05/22/2012 02:19 PM, Rich West wrote:
>> I noticed that going to 0.25 about a month back that the delay to start
>> playing an HD video had increased substantially and was curious as to
>> what might be the cause.
>>
>> As I looked further, I realized that it is with all video, but HD
>> content appears to be the most obvious offender. It can take up to 31
>> seconds from the moment the user selects the video to play before it
>> actually starts playing.
>>
>> My backend system is well used, but from the graphs I have, it's not
>> hurting with CPU or memory. Network to the frontends are all hardwired
>> (backend is gig, frontends are 100 meg). From a utilization
>> perspective, the drives on the backend server are always hovering at
>> around 85% utilization, which is good, and the general I/O on the drives
>> is not such that it would cause a negative impact.
>>
>> I am using commercial detection, so I do suspect that there is some form
>> of buffering going on, but for 31 seconds? No network errors on the
>> switch or the interface for the frontend or the backend. CPU
>> utilization on the frontend is low.. basically idle.
>>
>> I'm just wondering if there is a particular place within MythTV to look
>> (for example, I recently found that it was recommended that "quick
>> tuning" should be enabled for the hdhomerun)..
>>
>
> /me guesses you have MySQL data on a file system with barriers enabled.
>
> Mike

Thanks, Mike. You are right.. In my case, it was probably pre-0.25
since I had rebuilt the system after a failed root drive, and, as part
of the rebuild, went with a clean install of Fedora 16 (restoring my DB
from a nightly backup) which defaults to ext4.

The ext4 "barrier" is somewhat controversial in its functionality. I'll
tinker around with it and see if it helps. :)

-Rich

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