linux-kernel - Re: [PATCH v7 12/14] KVM: selftests: Add dirty ring buffer test

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Date:   Thu, 19 Mar 2020 13:02:01 -0400
From:   Peter Xu <peterx@...hat.com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     "Michael S . Tsirkin" <mst@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Yan Zhao <yan.y.zhao@...el.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Christophe de Dinechin <dinechin@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v7 12/14] KVM: selftests: Add dirty ring buffer test

On Wed, Mar 18, 2020 at 12:37:18PM -0400, Peter Xu wrote:
> +static void dirty_ring_collect_dirty_pages(struct kvm_vm *vm, int slot,
> +					   void *bitmap, uint32_t num_pages)
> +{
> +	/* We only have one vcpu */
> +	static uint32_t fetch_index = 0;
> +	uint32_t count = 0, cleared;
> +
> +	/*
> +	 * Before fetching the dirty pages, we need a vmexit of the
> +	 * worker vcpu to make sure the hardware dirty buffers were
> +	 * flushed.  This is not needed for dirty-log/clear-log tests
> +	 * because get dirty log will natually do so.
> +	 *
> +	 * For now we do it in the simple way - we simply wait until
> +	 * the vcpu uses up the soft dirty ring, then it'll always
> +	 * do a vmexit to make sure that PML buffers will be flushed.
> +	 * In real hypervisors, we probably need a vcpu kick or to
> +	 * stop the vcpus (before the final sync) to make sure we'll
> +	 * get all the existing dirty PFNs even cached in hardware.
> +	 */
> +	sem_wait(&dirty_ring_vcpu_stop);
> +
> +	/* Only have one vcpu */
> +	count = dirty_ring_collect_one(vcpu_map_dirty_ring(vm, VCPU_ID),
> +				       slot, bitmap, num_pages, &fetch_index);
> +
> +	cleared = kvm_vm_reset_dirty_ring(vm);
> +
> +	/* Cleared pages should be the same as collected */
> +	TEST_ASSERT(cleared == count, "Reset dirty pages (%u) mismatch "
> +		    "with collected (%u)", cleared, count);
> +
> +	DEBUG("Notifying vcpu to continue\n");

This line is removed later so hidden from my eyes too... but it'll
also break the bisection.  Fixed now.

> +	sem_post(&dirty_ring_vcpu_cont);
> +
> +	pr_info("Iteration %ld collected %u pages\n", iteration, count);
> +}

-- 
Peter Xu