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gen2

Member

Registered: 2006-09-07

Posts: 32

multi-io throughput issue

I seem to have an issue with multiple IO streams causing starvation.

For instance if I run 4 high-def videos (720p x264 mkv's), I get video stalls on all the videos. Its normally about 2 video streams that stall at a time, but cycles through each of the 4 video's that are playing. I can get this happen even with 3 video streams playing.

I'm using mplayer with xv video output module.

My system:
Linux skynet 2.6.29-ARCH #1 SMP PREEMPT Wed Apr 8 12:39:28 CEST 2009 x86_64 Dual Core AMD Opteron(tm) Processor 280 AuthenticAMD GNU/Linux

If i run top, the 4 video's are using about 20% cpu each. I have a dual dual core system, so thats fine, one CPU each.

Ram isn't a problem, I have 6gigs of it.

If I run iotop, the 4 video's are at the top pulling about 400-600kB/sec.

Now I know my harddrives which are on a Areca Raid 6 array (6x1TB drives), can do 300MB/sec burst and about 150MB/sec sustained. But this would be linear access with only one IO process running (the benchmark program).

This is on a XFS filesystem.

It seems the issue arises when I have more than one process accessing this array. It even seems to cause response issues on my desktop environment.

This issue can also be simulated if I open up DC++ and get 10 clients to download a random set of files of the drives. In this case the array is able to pull 80MB/sec but the graph shows small periods of no IO probably due to something not servicing the processes, but my desktop interactivity performance suffers.

Any ideas?, any benchmarks you need me to run to get a better idea of whats going on?

Last edited by gen2 (2009-05-14 14:25:40)

gen2

Member

Registered: 2006-09-07

Posts: 32

Re: multi-io throughput issue

Whats interesting is that using iostat with iozone i get very good performance on the array.

iostat records up to 2500 TPS (Transactions per second, IOPs)

And iozone records in throughput mode (4 processes writing 2G files) consitently over 200MB/sec reads and writes total. However each process gets about 50MB/sec.

Which means I can handle multiple IO, just that when it comes to running apps like mplayer with multiple videos or direct connect it starts to stall.

IOstat with mplayer running 4 HD vids only show 4 TPS. and around 2MB/sec.