linux-kernel - Re: [PATCH 2/2] KVM: selftests: Enable dirty_log

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Date:   Tue, 30 Jul 2019 19:11:23 +0200
From:   Thomas Huth <thuth@...hat.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        kvm@...r.kernel.org, Janosch Frank <frankja@...ux.ibm.com>
Cc:     linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Shuah Khan <shuah@...nel.org>, Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH 2/2] KVM: selftests: Enable dirty_log_test on s390x

On 30/07/2019 16.57, Christian Borntraeger wrote:
> 
> 
> On 30.07.19 12:01, Thomas Huth wrote:
>> To run the dirty_log_test on s390x, we have to make sure that we
>> access the dirty log bitmap with little endian byte ordering and
>> we have to properly align the memslot of the guest.
>> Also all dirty bits of a segment are set once on s390x when one
>> of the pages of a segment are written to for the first time, so
>> we have to make sure that we touch all pages during the first
>> iteration to keep the test in sync here.
> 
> While this fixes the test (and the migration does work fine), it still
> means that s390x overindicates the dirty bit for sparsely populated
> 1M segments. It is just a performance issue, but maybe we should try 
> to get this fixed.

I hope you don't expect me to fix this - the gmap code is really not my
turf...

> Not sure what to do here to remember us about this, 
> adding this as expected fail?

There is no such thing like an expected failure in KVM selftests -
that's only available in kvm-unit-tests.

So the only option that I currently see is to add a printf("TODO: ...")
on s390x here... would that work for you?

 Thomas