Message ID | 20220829165659.96046-2-peterx@redhat.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | migration: Postcopy Preempt-Full | expand |
* Peter Xu (peterx@redhat.com) wrote: > Since we already have bitmap_mutex to protect either the dirty bitmap or > the clear log bitmap, we don't need atomic operations to set/clear/test on > the clear log bitmap. Switching all ops from atomic to non-atomic > versions, meanwhile touch up the comments to show which lock is in charge. > > Introduced non-atomic version of bitmap_test_and_clear_atomic(), mostly the > same as the atomic version but simplified a few places, e.g. dropped the > "old_bits" variable, and also the explicit memory barriers. > > Signed-off-by: Peter Xu <peterx@redhat.com> Can you update the comment in ramblock.h above clear_bmap to say it's always updated under that lock. Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> > --- > include/exec/ram_addr.h | 11 +++++----- > include/qemu/bitmap.h | 1 + > util/bitmap.c | 45 +++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 52 insertions(+), 5 deletions(-) > > diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h > index f3e0c78161..5092a2e0ff 100644 > --- a/include/exec/ram_addr.h > +++ b/include/exec/ram_addr.h > @@ -42,7 +42,8 @@ static inline long clear_bmap_size(uint64_t pages, uint8_t shift) > } > > /** > - * clear_bmap_set: set clear bitmap for the page range > + * clear_bmap_set: set clear bitmap for the page range. Must be with > + * bitmap_mutex held. > * > * @rb: the ramblock to operate on > * @start: the start page number > @@ -55,12 +56,12 @@ static inline void clear_bmap_set(RAMBlock *rb, uint64_t start, > { > uint8_t shift = rb->clear_bmap_shift; > > - bitmap_set_atomic(rb->clear_bmap, start >> shift, > - clear_bmap_size(npages, shift)); > + bitmap_set(rb->clear_bmap, start >> shift, clear_bmap_size(npages, shift)); > } > > /** > - * clear_bmap_test_and_clear: test clear bitmap for the page, clear if set > + * clear_bmap_test_and_clear: test clear bitmap for the page, clear if set. > + * Must be with bitmap_mutex held. > * > * @rb: the ramblock to operate on > * @page: the page number to check > @@ -71,7 +72,7 @@ static inline bool clear_bmap_test_and_clear(RAMBlock *rb, uint64_t page) > { > uint8_t shift = rb->clear_bmap_shift; > > - return bitmap_test_and_clear_atomic(rb->clear_bmap, page >> shift, 1); > + return bitmap_test_and_clear(rb->clear_bmap, page >> shift, 1); > } > > static inline bool offset_in_ramblock(RAMBlock *b, ram_addr_t offset) > diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h > index 82a1d2f41f..3ccb00865f 100644 > --- a/include/qemu/bitmap.h > +++ b/include/qemu/bitmap.h > @@ -253,6 +253,7 @@ void bitmap_set(unsigned long *map, long i, long len); > void bitmap_set_atomic(unsigned long *map, long i, long len); > void bitmap_clear(unsigned long *map, long start, long nr); > bool bitmap_test_and_clear_atomic(unsigned long *map, long start, long nr); > +bool bitmap_test_and_clear(unsigned long *map, long start, long nr); > void bitmap_copy_and_clear_atomic(unsigned long *dst, unsigned long *src, > long nr); > unsigned long bitmap_find_next_zero_area(unsigned long *map, > diff --git a/util/bitmap.c b/util/bitmap.c > index f81d8057a7..8d12e90a5a 100644 > --- a/util/bitmap.c > +++ b/util/bitmap.c > @@ -240,6 +240,51 @@ void bitmap_clear(unsigned long *map, long start, long nr) > } > } > > +bool bitmap_test_and_clear(unsigned long *map, long start, long nr) > +{ > + unsigned long *p = map + BIT_WORD(start); > + const long size = start + nr; > + int bits_to_clear = BITS_PER_LONG - (start % BITS_PER_LONG); > + unsigned long mask_to_clear = BITMAP_FIRST_WORD_MASK(start); > + bool dirty = false; > + > + assert(start >= 0 && nr >= 0); > + > + /* First word */ > + if (nr - bits_to_clear > 0) { > + if ((*p) & mask_to_clear) { > + dirty = true; > + } > + *p &= ~mask_to_clear; > + nr -= bits_to_clear; > + bits_to_clear = BITS_PER_LONG; > + p++; > + } > + > + /* Full words */ > + if (bits_to_clear == BITS_PER_LONG) { > + while (nr >= BITS_PER_LONG) { > + if (*p) { > + dirty = true; > + *p = 0; > + } > + nr -= BITS_PER_LONG; > + p++; > + } > + } > + > + /* Last word */ > + if (nr) { > + mask_to_clear &= BITMAP_LAST_WORD_MASK(size); > + if ((*p) & mask_to_clear) { > + dirty = true; > + } > + *p &= ~mask_to_clear; > + } > + > + return dirty; > +} > + > bool bitmap_test_and_clear_atomic(unsigned long *map, long start, long nr) > { > unsigned long *p = map + BIT_WORD(start); > -- > 2.32.0 >
On Thu, Sep 15, 2022 at 07:49:57PM +0100, Dr. David Alan Gilbert wrote: > * Peter Xu (peterx@redhat.com) wrote: > > Since we already have bitmap_mutex to protect either the dirty bitmap or > > the clear log bitmap, we don't need atomic operations to set/clear/test on > > the clear log bitmap. Switching all ops from atomic to non-atomic > > versions, meanwhile touch up the comments to show which lock is in charge. > > > > Introduced non-atomic version of bitmap_test_and_clear_atomic(), mostly the > > same as the atomic version but simplified a few places, e.g. dropped the > > "old_bits" variable, and also the explicit memory barriers. > > > > Signed-off-by: Peter Xu <peterx@redhat.com> > > Can you update the comment in ramblock.h above clear_bmap to say it's > always updated under that lock. I'll squash below into the same patch: ---8<--- diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h index 6cbedf9e0c..adc03df59c 100644 --- a/include/exec/ramblock.h +++ b/include/exec/ramblock.h @@ -53,6 +53,9 @@ struct RAMBlock { * and split clearing of dirty bitmap on the remote node (e.g., * KVM). The bitmap will be set only when doing global sync. * + * It is only used during src side of ram migration, and it is + * protected by the global ram_state.bitmap_mutex. + * * NOTE: this bitmap is different comparing to the other bitmaps * in that one bit can represent multiple guest pages (which is * decided by the `clear_bmap_shift' variable below). On ---8<--- > > Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Thanks,
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h index f3e0c78161..5092a2e0ff 100644 --- a/include/exec/ram_addr.h +++ b/include/exec/ram_addr.h @@ -42,7 +42,8 @@ static inline long clear_bmap_size(uint64_t pages, uint8_t shift) } /** - * clear_bmap_set: set clear bitmap for the page range + * clear_bmap_set: set clear bitmap for the page range. Must be with + * bitmap_mutex held. * * @rb: the ramblock to operate on * @start: the start page number @@ -55,12 +56,12 @@ static inline void clear_bmap_set(RAMBlock *rb, uint64_t start, { uint8_t shift = rb->clear_bmap_shift; - bitmap_set_atomic(rb->clear_bmap, start >> shift, - clear_bmap_size(npages, shift)); + bitmap_set(rb->clear_bmap, start >> shift, clear_bmap_size(npages, shift)); } /** - * clear_bmap_test_and_clear: test clear bitmap for the page, clear if set + * clear_bmap_test_and_clear: test clear bitmap for the page, clear if set. + * Must be with bitmap_mutex held. * * @rb: the ramblock to operate on * @page: the page number to check @@ -71,7 +72,7 @@ static inline bool clear_bmap_test_and_clear(RAMBlock *rb, uint64_t page) { uint8_t shift = rb->clear_bmap_shift; - return bitmap_test_and_clear_atomic(rb->clear_bmap, page >> shift, 1); + return bitmap_test_and_clear(rb->clear_bmap, page >> shift, 1); } static inline bool offset_in_ramblock(RAMBlock *b, ram_addr_t offset) diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h index 82a1d2f41f..3ccb00865f 100644 --- a/include/qemu/bitmap.h +++ b/include/qemu/bitmap.h @@ -253,6 +253,7 @@ void bitmap_set(unsigned long *map, long i, long len); void bitmap_set_atomic(unsigned long *map, long i, long len); void bitmap_clear(unsigned long *map, long start, long nr); bool bitmap_test_and_clear_atomic(unsigned long *map, long start, long nr); +bool bitmap_test_and_clear(unsigned long *map, long start, long nr); void bitmap_copy_and_clear_atomic(unsigned long *dst, unsigned long *src, long nr); unsigned long bitmap_find_next_zero_area(unsigned long *map, diff --git a/util/bitmap.c b/util/bitmap.c index f81d8057a7..8d12e90a5a 100644 --- a/util/bitmap.c +++ b/util/bitmap.c @@ -240,6 +240,51 @@ void bitmap_clear(unsigned long *map, long start, long nr) } } +bool bitmap_test_and_clear(unsigned long *map, long start, long nr) +{ + unsigned long *p = map + BIT_WORD(start); + const long size = start + nr; + int bits_to_clear = BITS_PER_LONG - (start % BITS_PER_LONG); + unsigned long mask_to_clear = BITMAP_FIRST_WORD_MASK(start); + bool dirty = false; + + assert(start >= 0 && nr >= 0); + + /* First word */ + if (nr - bits_to_clear > 0) { + if ((*p) & mask_to_clear) { + dirty = true; + } + *p &= ~mask_to_clear; + nr -= bits_to_clear; + bits_to_clear = BITS_PER_LONG; + p++; + } + + /* Full words */ + if (bits_to_clear == BITS_PER_LONG) { + while (nr >= BITS_PER_LONG) { + if (*p) { + dirty = true; + *p = 0; + } + nr -= BITS_PER_LONG; + p++; + } + } + + /* Last word */ + if (nr) { + mask_to_clear &= BITMAP_LAST_WORD_MASK(size); + if ((*p) & mask_to_clear) { + dirty = true; + } + *p &= ~mask_to_clear; + } + + return dirty; +} + bool bitmap_test_and_clear_atomic(unsigned long *map, long start, long nr) { unsigned long *p = map + BIT_WORD(start);
Since we already have bitmap_mutex to protect either the dirty bitmap or the clear log bitmap, we don't need atomic operations to set/clear/test on the clear log bitmap. Switching all ops from atomic to non-atomic versions, meanwhile touch up the comments to show which lock is in charge. Introduced non-atomic version of bitmap_test_and_clear_atomic(), mostly the same as the atomic version but simplified a few places, e.g. dropped the "old_bits" variable, and also the explicit memory barriers. Signed-off-by: Peter Xu <peterx@redhat.com> --- include/exec/ram_addr.h | 11 +++++----- include/qemu/bitmap.h | 1 + util/bitmap.c | 45 +++++++++++++++++++++++++++++++++++++++++ 3 files changed, 52 insertions(+), 5 deletions(-)