linux-kernel - Re: [PATCH 2/6] KVM: selftests: Avoid flooding debug log while populating memory

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Date:   Fri, 15 Jan 2021 16:00:24 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Ben Gardon <bgardon@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Andrew Jones <drjones@...hat.com>,
        Peter Shier <pshier@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Thomas Huth <thuth@...hat.com>, Jacob Xu <jacobhxu@...gle.com>,
        Makarand Sonare <makarandsonare@...gle.com>
Subject: Re: [PATCH 2/6] KVM: selftests: Avoid flooding debug log while
 populating memory

On Tue, Jan 12, 2021, Ben Gardon wrote:
> Peter Xu pointed out that a log message printed while waiting for the
> memory population phase of the dirty_log_perf_test will flood the debug
> logs as there is no delay after printing the message. Since the message
> does not provide much value anyway, remove it.

Does it provide value if something goes wrong?  E.g. if a vCPU doesn't finish,
how would one go about debugging?  Would it make sense to make the print
ratelimited instead of removing it altogether?
 
> Reviewed-by: Jacob Xu <jacobhxu@...gle.com>
> 
> Signed-off-by: Ben Gardon <bgardon@...gle.com>
> ---
>  tools/testing/selftests/kvm/dirty_log_perf_test.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/dirty_log_perf_test.c b/tools/testing/selftests/kvm/dirty_log_perf_test.c
> index 16efe6589b43..15a9c45bdb5f 100644
> --- a/tools/testing/selftests/kvm/dirty_log_perf_test.c
> +++ b/tools/testing/selftests/kvm/dirty_log_perf_test.c
> @@ -146,8 +146,7 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>  	/* Allow the vCPU to populate memory */
>  	pr_debug("Starting iteration %lu - Populating\n", iteration);
>  	while (READ_ONCE(vcpu_last_completed_iteration[vcpu_id]) != iteration)
> -		pr_debug("Waiting for vcpu_last_completed_iteration == %lu\n",
> -			iteration);
> +		;
>  
>  	ts_diff = timespec_elapsed(start);
>  	pr_info("Populate memory time: %ld.%.9lds\n",
> @@ -171,9 +170,9 @@ static void run_test(enum vm_guest_mode mode, void *arg)
>  
>  		pr_debug("Starting iteration %lu\n", iteration);
>  		for (vcpu_id = 0; vcpu_id < nr_vcpus; vcpu_id++) {
> -			while (READ_ONCE(vcpu_last_completed_iteration[vcpu_id]) != iteration)
> -				pr_debug("Waiting for vCPU %d vcpu_last_completed_iteration == %lu\n",
> -					 vcpu_id, iteration);
> +			while (READ_ONCE(vcpu_last_completed_iteration[vcpu_id])
> +			       != iteration)

I like the original better.  Poking out past 80 chars isn't the end of the world.

> +				;
>  		}
>  
>  		ts_diff = timespec_elapsed(start);
> -- 
> 2.30.0.284.gd98b1dd5eaa7-goog
>