From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46068) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YxE2D-0004US-NB for qemu-devel@nongnu.org; Tue, 26 May 2015 08:32:42 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YxE27-00044X-U4 for qemu-devel@nongnu.org; Tue, 26 May 2015 08:32:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55514) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YxE27-00044C-Nk for qemu-devel@nongnu.org; Tue, 26 May 2015 08:32:35 -0400 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) by mx1.redhat.com (Postfix) with ESMTPS id 41E9CBDD7C for ; Tue, 26 May 2015 12:32:35 +0000 (UTC) Date: Tue, 26 May 2015 20:32:32 +0800 From: Fam Zheng Message-ID: <20150526123232.GF27391@ad.nay.redhat.com> References: <1430152117-100558-1-git-send-email-pbonzini@redhat.com> <1430152117-100558-25-git-send-email-pbonzini@redhat.com> <20150526122734.GW13749@ad.nay.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150526122734.GW13749@ad.nay.redhat.com> Subject: Re: [Qemu-devel] [PATCH 24/29] bitmap: add atomic test and clear List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: qemu-devel@nongnu.org, stefanha@redhat.com, mst@redhat.com On Tue, 05/26 20:27, Fam Zheng wrote: > On Mon, 04/27 18:28, Paolo Bonzini wrote: > > From: Stefan Hajnoczi > > > > The new bitmap_test_and_clear_atomic() function clears a range and > > returns whether or not the bits were set. > > > > Signed-off-by: Stefan Hajnoczi > > Message-Id: <1417519399-3166-3-git-send-email-stefanha@redhat.com> > > [Test before xchg; then a full barrier is needed at the end just like > > in the previous patch. The barrier can be avoided if we did at least > > one xchg. - Paolo] > > > > Signed-off-by: Paolo Bonzini > > --- > > include/qemu/bitmap.h | 2 ++ > > util/bitmap.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ > > 2 files changed, 46 insertions(+) > > > > diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h > > index 3e0a4f3..86dd9cd 100644 > > --- a/include/qemu/bitmap.h > > +++ b/include/qemu/bitmap.h > > @@ -41,6 +41,7 @@ > > * bitmap_set(dst, pos, nbits) Set specified bit area > > * bitmap_set_atomic(dst, pos, nbits) Set specified bit area with atomic ops > > * bitmap_clear(dst, pos, nbits) Clear specified bit area > > + * bitmap_test_and_clear_atomic(dst, pos, nbits) Test and clear area > > * bitmap_find_next_zero_area(buf, len, pos, n, mask) Find bit free area > > */ > > > > @@ -229,6 +230,7 @@ static inline int bitmap_intersects(const unsigned long *src1, > > 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); > > unsigned long bitmap_find_next_zero_area(unsigned long *map, > > unsigned long size, > > unsigned long start, > > diff --git a/util/bitmap.c b/util/bitmap.c > > index 6838d49..d3e088d 100644 > > --- a/util/bitmap.c > > +++ b/util/bitmap.c > > @@ -234,6 +234,50 @@ void bitmap_clear(unsigned long *map, long start, long nr) > > } > > } > > > > +bool bitmap_test_and_clear_atomic(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); > > + unsigned long dirty = 0; > > + unsigned long old_bits; > > + > > + /* First word */ > > + if (nr - bits_to_clear > 0) { > > + old_bits = atomic_fetch_and(p, ~mask_to_clear); > > + dirty |= old_bits & mask_to_clear; > > + nr -= bits_to_clear; > > + bits_to_clear = BITS_PER_LONG; > > + mask_to_clear = ~0UL; > > + p++; > > + } > > + > > It's broken if the clear range is the last part of first word: > > map = 0xFFFFFFFFFFFFFFFF, ... > > bitmap_test_and_clear_atomic(map, 60, 4): > > Expected result: > > 0xFFFFFFFFFFFFFFFF, ... Sorry, I meant 0xFFFFFFFFFFFFFFF (the highest 4 bits being cleared). > > Actual result: > > 0x0 > > Fam >