[PATCH 2/2] selftests/powerpc: Calculate spin time in tm-unavailable

[Cyril Bur]

On Mon, 2017-12-11 at 13:02 +1100, Michael Ellerman wrote:

> Cyril Bur <cyrilbur at gmail.com> writes:

>

> > On Tue, 2017-11-21 at 11:31 -0200, Gustavo Romero wrote:

> > > Hi Cyril,

> > >

> > > On 21-11-2017 05:17, Cyril Bur wrote:

> > > > Currently the tm-unavailable test spins for a fixed amount of time in

> > > > an attempt to ensure the FPU/VMX/VSX facilities are off. This value was

> > > > experimentally tested to be long enough.

> > > >

> > > > Problems may arise if kernel heuristics were to change. This patch

> > > > should future proof this test.

> > >

> > > I've tried it on a VM running on '4.14.0-rc7' and apparently it gets stuck

> > > pretty slow on calibration, since it ran ~7m without finding the correct value

> > > (before it would take about 3m), like:

> > >

> > > $ time ./tm-unavailable

> > > Testing required spin time required for facility unavailable...

> > > 	Trying 0x18000000...

> > > 	Trying 0x19000000...

> > > 	Trying 0x1a000000...

> > > ...

> > > 	Trying 0xfd000000... ^C

> > >

> > > real	7m15.304s

> > > user	7m15.291s

> > > sys	0m0.004s

> > >

> >

> > Interesting! I didn't test in a VM. I guess hypervisor switching

> > completely changes the heuristic. Ok I'll have to rethink.

> >

> > Maybe the increase should be a multiplier to get to a good state more

> > quickly.

>

> Yeah this sucks in a VM:

>

> # /home/michael/tm-unavailable

> Testing required spin time required for facility unavailable...

> 	Trying 0x18000000...

> 	Trying 0x19000000...

> ...

> 	Trying 0x110000000...

>

> etc.

>

> I got sick of waiting for it, but it's causing my selftests job to time

> out so it must be taking > ~1 hour.

>


Yeah sorry, I'll see if I can come up with a better way for a VM. Needs a
few more cycles from me.

Cyril

> cheers
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