linux-kernel - Re: [PATCH 05/20] KVM: selftests: Precisely track number of dirty/clear pages for each iteration

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Message-ID: <5b5b12bdc8a653901f28c754fcdced9103ae5c27.camel@redhat.com>
Date: Tue, 17 Dec 2024 18:59:42 -0500
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
 <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, Peter Xu
	 <peterx@...hat.com>
Subject: Re: [PATCH 05/20] KVM: selftests: Precisely track number of
 dirty/clear pages for each iteration

On Fri, 2024-12-13 at 17:07 -0800, Sean Christopherson wrote:
> Track and print the number of dirty and clear pages for each iteration.
> This provides parity between all log modes, and will allow collecting the
> dirty ring multiple times per iteration without spamming the console.
> 
> Opportunistically drop the "Dirtied N pages" print, which is redundant
> and wrong.  For the dirty ring testcase, the vCPU isn't guaranteed to
> complete a loop.  And when the vCPU does complete a loot, there are no
Typo
> guarantees that it has *dirtied* that many pages; because the writes are
> to random address, the vCPU may have written the same page over and over,
> i.e. only dirtied one page.

Counting how many times a vCPU wrote is also a valid statistic

I think it would be the best to include it as well (e.g call it number of
loops that vCPU did).

Best regards,
	Maxim Levitsky

> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  tools/testing/selftests/kvm/dirty_log_test.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
> index 55a744373c80..08cbecd1a135 100644
> --- a/tools/testing/selftests/kvm/dirty_log_test.c
> +++ b/tools/testing/selftests/kvm/dirty_log_test.c
> @@ -388,8 +388,6 @@ static void dirty_ring_collect_dirty_pages(struct kvm_vcpu *vcpu, int slot,
>  
>  	if (READ_ONCE(dirty_ring_vcpu_ring_full))
>  		dirty_ring_continue_vcpu();
> -
> -	pr_info("Iteration %ld collected %u pages\n", iteration, count);
>  }
>  
>  static void dirty_ring_after_vcpu_run(struct kvm_vcpu *vcpu)
> @@ -508,24 +506,20 @@ static void log_mode_after_vcpu_run(struct kvm_vcpu *vcpu)
>  static void *vcpu_worker(void *data)
>  {
>  	struct kvm_vcpu *vcpu = data;
> -	uint64_t pages_count = 0;
>  
>  	while (!READ_ONCE(host_quit)) {
> -		pages_count += TEST_PAGES_PER_LOOP;
>  		/* Let the guest dirty the random pages */
>  		vcpu_run(vcpu);
>  		log_mode_after_vcpu_run(vcpu);
>  	}
>  
> -	pr_info("Dirtied %"PRIu64" pages\n", pages_count);
> -
>  	return NULL;
>  }
>  
>  static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
>  {
> +	uint64_t page, nr_dirty_pages = 0, nr_clean_pages = 0;
>  	uint64_t step = vm_num_host_pages(mode, 1);
> -	uint64_t page;
>  	uint64_t *value_ptr;
>  	uint64_t min_iter = 0;
>  
> @@ -544,7 +538,7 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
>  		if (__test_and_clear_bit_le(page, bmap)) {
>  			bool matched;
>  
> -			host_dirty_count++;
> +			nr_dirty_pages++;
>  
>  			/*
>  			 * If the bit is set, the value written onto
> @@ -605,7 +599,7 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
>  				    " incorrect (iteration=%"PRIu64")",
>  				    page, *value_ptr, iteration);
>  		} else {
> -			host_clear_count++;
> +			nr_clean_pages++;
>  			/*
>  			 * If cleared, the value written can be any
>  			 * value smaller or equals to the iteration
> @@ -639,6 +633,12 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
>  			}
>  		}
>  	}
> +
> +	pr_info("Iteration %2ld: dirty: %-6lu clean: %-6lu\n",
> +		iteration, nr_dirty_pages, nr_clean_pages);
> +
> +	host_dirty_count += nr_dirty_pages;
> +	host_clear_count += nr_clean_pages;
>  }
>  
>  static struct kvm_vm *create_vm(enum vm_guest_mode mode, struct kvm_vcpu **vcpu,