linux-kernel - Re: [PATCH 14/20] KVM: selftests: Collect *all* dirty entries in each dirty_log

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Message-ID: <680a0b7b95b9300d2972246fbfd93f000ce0c0be.camel@redhat.com>
Date: Thu, 19 Dec 2024 10:01:32 -0500
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson
 <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, Peter Xu
	 <peterx@...hat.com>
Subject: Re: [PATCH 14/20] KVM: selftests: Collect *all* dirty entries in
 each dirty_log_test iteration

On Thu, 2024-12-19 at 13:55 +0100, Paolo Bonzini wrote:
> On 12/19/24 03:13, Sean Christopherson wrote:
> > On Tue, Dec 17, 2024, Maxim Levitsky wrote:
> > > While this patch might improve coverage for this particular case,
> > > I think that this patch will make the test to be much more deterministic,
> > 
> > The verification will be more deterministic, but the actual testcase itself is
> > just as random as it was before.
> 
> Based on my recollection of designing this thing with Peter, I can 
> "confirm" that there was no particular intention of making the 
> verification more random.
> 
> > > and thus have less chance of catching various races in the kernel that can happen.
> > > 
> > > In fact in my option I prefer moving this test in other direction by
> > > verifying dirty ring while the *vCPU runs* as well, in other words, not
> > > stopping the vCPU at all unless its dirty ring is full.
> > 
> > But letting the vCPU-under-test keep changing the memory while it's being validated
> > would add significant complexity, without any benefit insofar as I can see.  As
> > evidenced by the bug the current approach can't detect, heavily stressing the
> > system is meaningless if it's impossible to separate the signal from the noise.
> 
> Yes, I agree.
> 
> Paolo
> 

In this case I don't have any objections.

Best regards,
	Maxim Levitsky