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From: Greg Kurz <groug@kaod.org>
To: Thomas Huth <thuth@redhat.com>
Cc: "Cédric Le Goater" <clg@kaod.org>,
	qemu-devel@nongnu.org,
	"David Gibson" <david@gibson.dropbear.id.au>
Subject: Re: [Qemu-devel] [PATCH for-3.1] tests/cpu-plug-test: check CPU hotplug on ppc64 with KVM
Date: Fri, 27 Jul 2018 14:03:39 +0200	[thread overview]
Message-ID: <20180727140339.4b936931@bahia> (raw)
In-Reply-To: <45f3757c-9c29-a894-d709-ba69ea9e9087@redhat.com>

On Fri, 27 Jul 2018 13:25:33 +0200
Thomas Huth <thuth@redhat.com> wrote:

> On 07/27/2018 11:00 AM, Greg Kurz wrote:
> > On Fri, 27 Jul 2018 10:18:14 +0200
> > Thomas Huth <thuth@redhat.com> wrote:
> >   
> >> On 07/27/2018 09:54 AM, Greg Kurz wrote:  
> >>> On Fri, 27 Jul 2018 15:27:24 +1000
> >>> David Gibson <david@gibson.dropbear.id.au> wrote:
> >>>     
> >>>> On Wed, Jul 25, 2018 at 04:45:26PM +0200, Greg Kurz wrote:    
> >>>>> Commit b585395b655 fixed a regression introduced by some recent changes
> >>>>> in the XICS code, that was causing QEMU to crash instantly during CPU
> >>>>> hotplug with KVM. This is typically the kind of bug we'd like our
> >>>>> test suite to detect before it gets merged. Unfortunately, the current
> >>>>> tests run with '-machine accel=qtest' and don't exercise KVM specific
> >>>>> paths in QEMU.
> >>>>>
> >>>>> This patch hence changes add_pseries_test_case() to launch QEMU with
> >>>>> '-machine accel=kvm' if KVM is available.
> >>>>>
> >>>>> A notable consequence is that the guest will execute SLOF, but for some
> >>>>> reasons SLOF sometimes hits a program exception. This causes the guest
> >>>>> to loop forever and the test to be stuck.  Since we don't need the guest
> >>>>> to be truely running, let's pass -S to QEMU to avoid that.
> >>>>>
> >>>>> Also disable machine capabilities that could be unavailable in KVM, eg,
> >>>>> when using PR KVM.
> >>>>>
> >>>>> Signed-off-by: Greg Kurz <groug@kaod.org>      
> >>>>
> >>>> I'm pretty sure trying to change the accelerator on a qtest test just
> >>>> doesn't make sense.  We'd need a different approach for testing cpu
> >>>> hotplug against kvm & tcg backends.
> >>>>    
> >>>
> >>> The test starts QEMU, triggers the CPU hotplug code with a QMP command
> >>> and checks the command didn't fail (or QEMU didn't crash, as it would
> >>> have before commit b585395b655a)... I really don't understand what
> >>> is wrong with that... Please elaborate.    
> >>
> >> For a "real" test, I think you'd need a guest OS that is reacting to the
> >> hot plug events. So maybe this should rather be done in the avocado
> >> framework instead?
> >>  
> > 
> > The intent isn't a "real" test actually, but just to exercise the XICS-KVM
> > paths in QEMU that get called during CPU hotplug. This cannot be achieved
> > with the qtest accelerator.
> > 
> > This patch would have revealed the regression in b585395b655a right away,
> > with the simple 'make check' developers are expected to run before posting.  
> 
> OK, that's fair. I think what rather bugs me here is that you start QEMU
> with -S to work around something that sounds like real bug in SLOF ...
> any chance that you could fix that bug in SLOF instead of using -S here?
> 

Yeah, -S is a workaround indeed. I've chosen to go that way because I couldn't
find any impact on the hotplug path, but I may have overlooked something, so
I'm not surprised by your request :)

I guess that's fair too and I'll investigate.

Cheers,

--
Greg

>  Thomas

  reply	other threads:[~2018-07-27 12:03 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-25 14:45 Greg Kurz
2018-07-27  5:27 ` David Gibson
2018-07-27  7:54   ` Greg Kurz
2018-07-27  8:18     ` Thomas Huth
2018-07-27  9:00       ` Greg Kurz
2018-07-27 11:25         ` Thomas Huth
2018-07-27 12:03           ` Greg Kurz [this message]
2018-07-30  5:57     ` David Gibson
2018-07-30  8:41       ` Greg Kurz
2018-07-30  9:59         ` Greg Kurz
2018-07-31  3:27           ` David Gibson
2018-08-01 13:35             ` Greg Kurz
2018-07-31  3:25         ` David Gibson
2018-08-01 13:24           ` Greg Kurz
2018-08-02  4:08             ` David Gibson
2018-08-02  9:36             ` Igor Mammedov
2018-08-02 10:52               ` Greg Kurz

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