Commit e46ad851 authored by Sean Christopherson's avatar Sean Christopherson
Browse files

KVM: Use mask of harvested dirty ring entries to coalesce dirty ring resets 



Use "mask" instead of a dedicated boolean to track whether or not there
is at least one to-be-reset entry for the current slot+offset.  In the
body of the loop, mask is zero only on the first iteration, i.e. !mask is
equivalent to first_round.

Opportunistically combine the adjacent "if (mask)" statements into a single
if-statement.

No functional change intended.

Cc: Peter Xu <peterx@redhat.com>
Cc: Yan Zhao <yan.y.zhao@intel.com>
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: default avatarPankaj Gupta <pankaj.gupta@amd.com>
Reviewed-by: default avatarJames Houghton <jthoughton@google.com>
Reviewed-by: default avatarBinbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: default avatarYan Zhao <yan.y.zhao@intel.com>
Reviewed-by: default avatarPeter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/20250516213540.2546077-6-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent ee188dea

virt/kvm/dirty_ring.c

+31 −33
Original line number Diff line number Diff line
@@ -121,7 +121,6 @@ int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring, 
	u64 cur_offset, next_offset;

	unsigned long mask = 0;

	struct kvm_dirty_gfn *entry;

	bool first_round = true;



	while (likely((*nr_entries_reset) < INT_MAX)) {

		if (signal_pending(current))
@@ -141,20 +140,20 @@ int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring, 
		ring->reset_index++;

		(*nr_entries_reset)++;



		if (mask) {

			/*

		 * While the size of each ring is fixed, it's possible for the

		 * ring to be constantly re-dirtied/harvested while the reset

		 * is in-progress (the hard limit exists only to guard against

		 * wrapping the count into negative space).

			 * While the size of each ring is fixed, it's possible

			 * for the ring to be constantly re-dirtied/harvested

			 * while the reset is in-progress (the hard limit exists

			 * only to guard against the count becoming negative).

			 */

		if (!first_round)

			cond_resched();



			/*

		 * Try to coalesce the reset operations when the guest is

		 * scanning pages in the same slot.

			 * Try to coalesce the reset operations when the guest

			 * is scanning pages in the same slot.

			 */

		if (!first_round && next_slot == cur_slot) {

			if (next_slot == cur_slot) {

				s64 delta = next_offset - cur_offset;



				if (delta >= 0 && delta < BITS_PER_LONG) {
@@ -172,11 +171,11 @@ int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring, 
			}



			/*

		 * Reset the slot for all the harvested entries that have been

		 * gathered, but not yet fully processed.

			 * Reset the slot for all the harvested entries that

			 * have been gathered, but not yet fully processed.

			 */

		if (mask)

			kvm_reset_dirty_gfn(kvm, cur_slot, cur_offset, mask);

		}



		/*

		 * The current slot was reset or this is the first harvested
@@ -185,7 +184,6 @@ int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring, 
		cur_slot = next_slot;

		cur_offset = next_offset;

		mask = 1;

		first_round = false;

	}



	/*