Re: [Xen-devel] a strange issue on disk scheduler in xen

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Mar 13, 2013 at 11:40:07PM -0700, smiler wrote:
> Hi all,
> 
> In Xen 4.0 with Linux 2.6.18.8, noop is default scheduler in dom U. In Xen
> 4.0 with Linux 2.6.31.8, CFQ is default scheduler in domU. In the both
> setup, CFQ is default scheduler in dom0. I compare the execution time of two
> seqenatil read applications run on a domU under noop of domU with under cfq
> of domU in both two Linux kernel.
> The sequential read application is generated by sysbench to read 1gb, like
> that: sysbench --num-threads=16 --test=fileio --file-total-size=1G
> --file-test-mode=seqrd prepare/run/cleanup
> 
> I find a strange phenomenon as following:
> in Xen 4.0 with Linux 2.6.18.8
> noop in domU
> seqrd 1: 34.90s seqrd2: 32.49s
> cfq in domU
> seqrd 1: 245.94s seqrd2: 256.09s
> In this situation, the execution time of seqrd under CFQ of domU is much
> worse than that under noop of domU.
> However, in Xen 4.0 with Linux 2.6.31.8:
> noop in domU
> seqrd1: 36.83s seqrd 2: 37.01s
> CFQ in domU
> seqrd1: 35.68s seqrd 2: 35.76s
> In this situation, the execution time of seqrd under CFQ of domU is almost
> same as under noop of domU.
> 
> The comparsion between noop and cfq of domU in Xen 4.0 with Linux 2.6.18 is
> so different from that in Xen 4.0 with Linux 2.6.31.8, It is very very
> strange. I also do the experiment in differnt machines, the results are
> same. So does anyone know the reason?

You are using ancient code. It might be very well that there were bugs in 
2.6.18.
> 
> 
> 
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> 
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