On Fri, May 16, 2025 at 02:35:39PM -0700, Sean Christopherson wrote:
> 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@xxxxxxxxxx>
> Cc: Yan Zhao <yan.y.zhao@xxxxxxxxx>
> Cc: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> Reviewed-by: Pankaj Gupta <pankaj.gupta@xxxxxxx>
> Reviewed-by: James Houghton <jthoughton@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> virt/kvm/dirty_ring.c | 60 +++++++++++++++++++++----------------------
> 1 file changed, 29 insertions(+), 31 deletions(-)
>
> diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c
> index 84c75483a089..54734025658a 100644
> --- a/virt/kvm/dirty_ring.c
> +++ b/virt/kvm/dirty_ring.c
> @@ -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))
> @@ -141,42 +140,42 @@ int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring,
> ring->reset_index++;
> (*nr_entries_reset)++;
>
> - /*
> - * 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).
> - */
> - if (!first_round)
> + 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 the count becoming negative).
> + */
> cond_resched();
>
> - /*
> - * Try to coalesce the reset operations when the guest is
> - * scanning pages in the same slot.
> - */
> - if (!first_round && next_slot == cur_slot) {
> - s64 delta = next_offset - cur_offset;
> + /*
> + * Try to coalesce the reset operations when the guest
> + * is scanning pages in the same slot.
> + */
> + if (next_slot == cur_slot) {
> + s64 delta = next_offset - cur_offset;
>
> - if (delta >= 0 && delta < BITS_PER_LONG) {
> - mask |= 1ull << delta;
> - continue;
> - }
> + if (delta >= 0 && delta < BITS_PER_LONG) {
> + mask |= 1ull << delta;
> + continue;
> + }
>
> - /* Backwards visit, careful about overflows! */
> - if (delta > -BITS_PER_LONG && delta < 0 &&
> - (mask << -delta >> -delta) == mask) {
> - cur_offset = next_offset;
> - mask = (mask << -delta) | 1;
> - continue;
> + /* Backwards visit, careful about overflows! */
> + if (delta > -BITS_PER_LONG && delta < 0 &&
> + (mask << -delta >> -delta) == mask) {
> + cur_offset = next_offset;
> + mask = (mask << -delta) | 1;
> + continue;
> + }
> }
> - }
>
> - /*
> - * Reset the slot for all the harvested entries that have been
> - * gathered, but not yet fully processed.
> - */
> - if (mask)
> + /*
> + * Reset the slot for all the harvested entries that
> + * have been gathered, but not yet fully processed.
> + */
> kvm_reset_dirty_gfn(kvm, cur_slot, cur_offset, mask);
Nit and feel free to ignore it :)
Would it be better to move the "cond_resched()" to here, i.e., executing it for
at most every 64 entries?
> + }
>
> /*
> * 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;
> }
>
> /*
> --
> 2.49.0.1112.g889b7c5bd8-goog
>
