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X-Received-From: 2a00:1450:4864:20::541 Subject: Re: [Qemu-devel] [PATCH v3 1/2] bitmap: get last word mask from nr directly X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Wei Yang Cc: quintela@redhat.com, corentincj@iksaif.net, pl@kamp.de, qemu-devel@nongnu.org, peterx@redhat.com, kraxel@redhat.com, Wei Yang Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Aug 12, 2019 at 06:18:43PM +0200, Paolo Bonzini wrote: >On 18/07/19 03:04, Wei Yang wrote: >> The value left in nr is the number of bits for the last word, which >> could be calculate the last word mask directly. >> >> Remove the unnecessary size. > >Hi, > >the value left in nr is _not_ the number of bits for the last word if >the start and the end are in the same word. For example, if start % >BITS_PER_LONG was 3 and nr == 1, you'd have: > >- before the patch BITMAP_LAST_WORD_MASK(4) > >- after the patch BITMAP_LAST_WORD_MASK(1) > You are right. I missed this case. Thanks for pointing out. >Paolo > >> Signed-off-by: Wei Yang >> >> --- >> v2: refine bitmap_set_atomic too, suggested from Peter >> --- >> util/bitmap.c | 9 +++------ >> 1 file changed, 3 insertions(+), 6 deletions(-) >> >> diff --git a/util/bitmap.c b/util/bitmap.c >> index 1753ff7f5b..5b15249796 100644 >> --- a/util/bitmap.c >> +++ b/util/bitmap.c >> @@ -160,7 +160,6 @@ int slow_bitmap_andnot(unsigned long *dst, const unsigned long *bitmap1, >> void bitmap_set(unsigned long *map, long start, long nr) >> { >> unsigned long *p = map + BIT_WORD(start); >> - const long size = start + nr; >> int bits_to_set = BITS_PER_LONG - (start % BITS_PER_LONG); >> unsigned long mask_to_set = BITMAP_FIRST_WORD_MASK(start); >> >> @@ -174,7 +173,7 @@ void bitmap_set(unsigned long *map, long start, long nr) >> p++; >> } >> if (nr) { >> - mask_to_set &= BITMAP_LAST_WORD_MASK(size); >> + mask_to_set &= BITMAP_LAST_WORD_MASK(nr); >> *p |= mask_to_set; >> } >> } >> @@ -182,7 +181,6 @@ void bitmap_set(unsigned long *map, long start, long nr) >> void bitmap_set_atomic(unsigned long *map, long start, long nr) >> { >> unsigned long *p = map + BIT_WORD(start); >> - const long size = start + nr; >> int bits_to_set = BITS_PER_LONG - (start % BITS_PER_LONG); >> unsigned long mask_to_set = BITMAP_FIRST_WORD_MASK(start); >> >> @@ -208,7 +206,7 @@ void bitmap_set_atomic(unsigned long *map, long start, long nr) >> >> /* Last word */ >> if (nr) { >> - mask_to_set &= BITMAP_LAST_WORD_MASK(size); >> + mask_to_set &= BITMAP_LAST_WORD_MASK(nr); >> atomic_or(p, mask_to_set); >> } else { >> /* If we avoided the full barrier in atomic_or(), issue a >> @@ -221,7 +219,6 @@ void bitmap_set_atomic(unsigned long *map, long start, long nr) >> void bitmap_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); >> >> @@ -235,7 +232,7 @@ void bitmap_clear(unsigned long *map, long start, long nr) >> p++; >> } >> if (nr) { >> - mask_to_clear &= BITMAP_LAST_WORD_MASK(size); >> + mask_to_clear &= BITMAP_LAST_WORD_MASK(nr); >> *p &= ~mask_to_clear; >> } >> } >> > -- Wei Yang Help you, Help me