[mythtv-users] system profiling / cpu usage revisited

Aike Terjung aike at terjung.net
Fri Jun 20 01:18:09 EDT 2003


sorry if i understand somthing wrong, but my english is not the best.

have you activated the DMA Mode for the harddisks? 

cu Aike

Am Donnerstag, 19. Juni 2003 23:06 schrieb Brian Lalor:
> Ok, I've been doing some poking around with iostat and vmstat.  I changed
> my settings so that I'm now doing MPEG-4 encoding (exact params not
> important ATM).  My CPU's at ~100% most of the time that this recording is
> taking place. iostat shows:
>
> Time: 03:44:55 PM
> avg-cpu:  %user   %nice    %sys   %idle
>            99.10    0.00    0.70    0.20
>
> Device:    rrqm/s wrqm/s   r/s   w/s  rsec/s  wsec/s    rkB/s    wkB/s \
> 	avgrq-sz avgqu-sz   await  svctm  %util
> /dev/hda     0.00  46.00  0.00  8.80    0.00  438.40     0.00   219.20 \
> 	 49.82 4294697.37    0.80 113.64 100.00
> /dev/hda5    0.00  45.00  0.00  6.40    0.00  411.20     0.00   205.60 \
> 	   64.25     0.06    0.94   0.47   0.30
>
> Top shows mythbackend as the biggest CPU hog currently (of course):
>    PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME CPU COMMAND
> 29384 myth       9   0 41700  31M  3360 S    98.3  6.3  17:47   0
> mythbackend
>
> Let me just preface my remarks by saying that I don't really know the first
> thing about the workings of the kernel and system tuning, but I really want
> to get this sorted out, as I see many people having these issues.  It may
> be a bad choice of hard drive or motherboard, but I want to get to the
> bottom of it.
>
> First, as iostat shows above (sorry for the line-wrapping), my CPU's maxxed
> out by user processes, not by the kernel.  Doesn't this mean that it is in
> fact mythbackend that is tying up the CPU by compressing the data, rather
> than (if %sys were very high) that the kernel was spending all of its time
> in I/O routines?
>
> Second, the wkB/s column shows that I'm dumping about 205kB to the
> partition (/dev/hda5 is where my recordings go) a second (or around 1 meg
> every four seconds).  hdparm tells me my disk throughput is around 30
> meg/s, so that should be plenty.  I don't know what to make of the write
> queue information.
>
> Lastly, here's some vmstat info:
>     procs                      memory      swap          io     system     
> cpu r  b  w   swpd   free   buff  cache   si   so    bi    bo   in    cs us
> sy id 1  0  0  17228   4408  41016 365680    0    0     0   198  164   296
> 100  0  0
>
> Again we see my CPU maxxed, plenty of un-used memory, a bunch of blocks
> being written to the disk and a butt-load of context switches in the last
> two seconds (time since the last report).  Does that seem like a lot?  I
> dunno. Maybe someone else can do a similar analysis on a similar machine
> that can do the MPEG-4 encoding without breaking a sweat?  Here's a
> breakdown of my hardware again:
> Asus A7V8X-X motherboard (via chipset)
> AMD AthlonXP 1700+
> 512MB PC2700 DDR RAM
> WinTV-dbx tuner card
> 120GB 7200RPM Hitachi IDE drive
> linux kernel 2.4.21 compiled exactly for my hardware (mostly as reported
> via lspci)
>
> Collecting data is easy.  Analyzing it is hard. :-)
>
> Thanks,
> B



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