Re: [Xen-devel] questions about the number of pending requests that the host system can detect

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

 On 08/11/2010 08:42 PM, Yuehai Xu wrote:
> However, the result turns out that my assumption is wrong. The number
> of pending requests, according to the trace of blktrace, is changing
> like this way: 9 8 7 6 5 4 3 2 1 1 1 2 3 4 5 4 3 2 1 1 1 2 3 4 5 6 7 8
> 8 8..., just like a curve.
>
> I am puzzled about this weird result. Can anybody explain what has
> happened between domU and dom0 for this result? Does this result make
> sense? or I did something wrong to get this result.
If you're using a journalled filesystem in the guest, it will be need to 
drain the IO queue periodically to control the write ordering.  You 
should also observe barrier writes in the blkfront stream.
    J

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