Re: [Xen-users] I/O issue in xen guest OS

[Radu Rendec <radu.rendec@xxxxxxx>]

On Mon, 2009-07-06 at 20:40 +0530, chandrashekar wrote:
> As you suggested I checked CPU % and there is no issue in CPU but I
> think this is issue with memory.
> 
> Please find the xm top for the same.
> 
> 
> xentop - 20:35:49   Xen 3.1.2-92.el5
> 2 domains: 1 running, 1 blocked, 0 paused, 0 crashed, 0 dying, 0
> shutdown
> Mem: 4193636k total, 4193292k used, 344k free    CPUs: 8 @ 2333MHz
> NAME STATE CPU(sec) CPU(%) MEM(k) MEM(%) MAXMEM(k) MAXMEM(%) VCPUS
> NETS NETTX(k) NETRX(k) VBDS VBD_OO VBD_RD VBD_WR SSID
> Domain-0 -----r     23050    0.7    2200640   52.5   no limit
> n/a     8    4      248  2101165    0        0  0        0    0
> guest --b---        3938    0.0    1945432   46.4    1945600      46.4
> 1    1  2197321  2803970    0        0 0        0    0

Chandru,

The memory seems to be (almost) equally splitted between dom0 and the
guest, and you have plenty of it.

But I think I got the explanation to your issue:

domU has only one VCPU, while dom0 has 8 CPUs; since I/O activity is
likely not to span across multiple CPUs, you have the following:

domU: 1 cpu (of 1) waiting 100% for I/O => 100% overall IOwait
dom0: 1 cpu (of 8) waiting 100% for I/0 => 1/8 * 100% overall IOwait

I think 1/8 * 100% is exactly your 12%

Cheers,

Radu



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