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Commit d14769377a247d4e7b570592a090474c8a059938

Authored by Takuya Yoshikawa
Committed by Avi Kivity
1 parent 039091875c

KVM: Remove test-before-set optimization for dirty bits 

As Avi pointed out, testing bit part in mark_page_dirty() was important
in the days of shadow paging, but currently EPT and NPT has already become
common and the chance of faulting a page more that once per iteration is
small. So let's remove the test bit to avoid extra access.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>

Showing 1 changed file with 1 additions and 3 deletions Side-by-side Diff

... ... @@ -1192,9 +1192,7 @@
1192 1192 if (memslot && memslot->dirty_bitmap) {
1193 1193 unsigned long rel_gfn = gfn - memslot->base_gfn;
1194 1194  
1195   - /* avoid RMW */
1196   - if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap))
1197   - generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
  1195 + generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
1198 1196 }
1199 1197 }
1200 1198