[mythtv-users] 'Wakeup' Delay on Idle Frontend

Jim Stichnoth stichnot at gmail.com
Thu Dec 10 22:59:22 UTC 2009


On Thu, Dec 10, 2009 at 2:12 PM, Mark Garland
<mythtvusers at markgarland.co.uk> wrote:
> Hi all,
>
> I've been running 0.22-fixes out of the (K)Ubuntu repos for about a month
> now and really like it.
>
> One thing I've noticed is that when my combined frontend/backend has been
> left idle at the menu for some time (say overnight, or all day), when you
> press a button on the remote (or keyboard) there is a 4-5 second delay
> before the frontend responds.  Normally, things like up and down work
> instantly, but changing between menu screens, especially going into "Watch
> Recordings", gives the delay.
>
> I don't think it is a resource issue - the machine has plenty of RAM, has an
> idle CPU, I can't hear any extensive harddisk accesses during the delay, and
> the database is optimised nightly and was blank 4 weeks ago (compressed back
> up size is <15mb).
> I also don't remember this happening in 0.21-fixes.
>
> I'll have to do some more investigation (i.e. monitoring the disk/cpu)
> before that first remote button push, but for the time being I wanted to ask
> if anyone else was experiecing this, or whether it was a known bug?

Try running this:

strace -p<pid_of_mythfrontend> -tt -T -e trace=file > strace_out.txt 2>&1

after the system has "cooled off" to capture the file system accesses
and their timestamps while the system warms up again.  Repeat this
(outputting to a different file) for a warmed-up system.  See if there
are any big jumps in the timestamps versus a fairly smooth transition.

I see the same behavior on my frontends.  They are diskless ION boxes,
so I was assuming it was an NFS issue and I have been slowly trying to
migrate the relevant files (theme graphics, image caches) into a
ramdisk, but the delays are still there.  Interesting to hear that the
same behavior shows up with a hard disk.  My strace output shows that
with the Blue Abstract theme, there are over 2000 file accesses to
draw the Watch Recordings page, with many of the files being queried
lots of times (200 in at least one case).

Jim


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