Re: [Xen-devel] [PATCH] libxl: Increase device model startup timeout to 1min.

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Anthony PERARD writes ("Re: [PATCH] libxl: Increase device model startup 
timeout to 1min."):
> On Mon, Jun 29, 2015 at 03:51:57PM +0100, Ian Campbell wrote:
> > Nor does it really answer Ian's question in
> > <21901.33163.547929.321814@xxxxxxxxxxxxxxxxxxxxxxxx> I think.
> 
> I only know what happen, not why it happen.
> 
> How could I investigate why qemu is taking so long after an mmap() syscall?
> I guest at that time, it is copying the library into memory.

Is the machine very busy at this time ?

If this is a stress test of some kind then I guess there are three
possible views:

  * The number and nature of parallel operations done in the stress
    test is unreasonable for the provided hardware:
      => the timeout is fine

  * The number and nature of parallel operations is reasonable for the
    provided hardware, and should not result in the toolstack domain
    being overloaded to the point where ld.so on qemu takes so long
      => the timeout is correct and there is an underlying bug
         (perhaps in Linux)

  * The number and nature of parallel operations is reasonable for
    the hardware, but might easily result in long delays in ld.so
    assembling qemu - that is, people expect to deploy Xen and then
    cause their toolstack domain to be massively `overloaded' and
    very slow
      => the timeout is too short

In the third case we probably need a general-purpose facility for
adjusting timeouts in general.  People who do not expect to overload
their toolstack domain should not be made to await massive timeout
values designed for people who do.

Ian.

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