Re: Serious performance issues

[Anthony Liguori <aliguori@us.ibm.com>]

Tommi Virtanen wrote:

> I tested the disk, it still transfers ~50MB/s. I don't seem to be
> suffering from PIO mode. Also, things running from RAM cache are as
> slow as from disk.

What version of Xen is this?

> Any hints on what to try next?

If you're running xen-unstable, try xen-2.0.x or vice versa.  Are you 
absolutely positive that you've got enough memory allocated to dom0?  
That you've got the proper IO chipset support built into the kernel?  
That you've really got tls disabled (if you just move tls after an app 
has already launched using it it will still be using it until you 
restart the app)?

These numbers seem too bad to be Xen's fault alone.  Do you have swap 
enabled?  Is there a great deal of swap activity?

Regards,
Anthony Liguori

> bw_mem
> -0.131072 1068.95
> +0.131072 4409.00
>
> bw_pipe
> -Pipe bandwidth: 85.42 MB/sec
> +Pipe bandwidth: 989.19 MB/sec
>
> bw_unix
> -AF_UNIX sock stream bandwidth: 104.75 MB/sec
> +AF_UNIX sock stream bandwidth: 968.87 MB/sec
>
> lat_ctx
> -"size=0k ovr=3.15
> -10 13.95
> +"size=0k ovr=1.09
> +10 0.94
>
> lat_fcntl
> -Fcntl lock latency: 43.2246 microseconds
> +Fcntl lock latency: 5.4676 microseconds
>
> lat_fifo
> -FIFO latency: 32.4076 microseconds
> +FIFO latency: 3.3622 microseconds
>
> lat_fs
> -0k     1000    18563   31549
> -1k     1000    6426    17887
> -4k     1000    6583    17826
> -10k    1000    3084    14989
> +0k     1000    63666   92541
> +1k     1000    24125   51193
> +4k     1000    25863   52089
> +10k    1000    12533   41564
>
> lat_pipe
> -Pipe latency: 31.0475 microseconds
> +Pipe latency: 5.4833 microseconds
>
> lat_proc
> -Process fork+exit: 789.2857 microseconds
> +Process fork+exit: 113.7347 microseconds
>
> lat_select
> -Select on 200 tcp fd's: 46.8159 microseconds
> +Select on 200 tcp fd's: 12.9369 microseconds
>
> lat_syscall
> -Simple syscall: 0.6188 microseconds
> +Simple syscall: 0.1547 microseconds
>
> lat_unix
> -AF_UNIX sock stream latency: 61.1547 microseconds
> +AF_UNIX sock stream latency: 21.7704 microseconds
>
>
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