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From: Thomas Huth <thuth@redhat.com>
To: Greg Kurz <groug@kaod.org>
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 13:25:33 +0200	[thread overview]
Message-ID: <45f3757c-9c29-a894-d709-ba69ea9e9087@redhat.com> (raw)
In-Reply-To: <20180727110000.16f55218@bahia>

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?

 Thomas

  reply	other threads:[~2018-07-27 11:25 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-25 14:45 [Qemu-devel] [PATCH for-3.1] tests/cpu-plug-test: check CPU hotplug on ppc64 with KVM 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 [this message]
2018-07-27 12:03           ` Greg Kurz
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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