From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56087) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a0sRe-0003hK-E4 for qemu-devel@nongnu.org; Mon, 23 Nov 2015 09:50:23 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a0sRa-00035E-7s for qemu-devel@nongnu.org; Mon, 23 Nov 2015 09:50:18 -0500 References: <1448013593-14282-1-git-send-email-famz@redhat.com> <1448013593-14282-2-git-send-email-famz@redhat.com> <5652D602.8010809@cn.fujitsu.com> <20151123091911.GB689@ad.usersys.redhat.com> <5652DB34.5090300@cn.fujitsu.com> <20151123095506.GC689@ad.usersys.redhat.com> From: Paolo Bonzini Message-ID: <56532796.6000702@redhat.com> Date: Mon, 23 Nov 2015 15:49:58 +0100 MIME-Version: 1.0 In-Reply-To: <20151123095506.GC689@ad.usersys.redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH for 2.6 1/3] backup: Use Bitmap to replace "s->bitmap" List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng , Wen Congyang Cc: Kevin Wolf , vsementsov@virtuozzo.com, qemu-block@nongnu.org, Jeff Cody , qemu-devel@nongnu.org, mreitz@redhat.com, jsnow@redhat.com On 23/11/2015 10:55, Fam Zheng wrote: >>> Why? I think bitmap_set is a better match with bitmap_new below. >> >> set_bit() is quicker than bitmap_set() if you only set one bit. > > How much quicker is it? This doesn't sound convincing enough for me to lose the > readability. Substantially. It's also documented: /* * Also the following operations apply to bitmaps. * * set_bit(bit, addr) *addr |= bit * clear_bit(bit, addr) *addr &= ~bit * change_bit(bit, addr) *addr ^= bit * test_bit(bit, addr) Is bit set in *addr? * test_and_set_bit(bit, addr) Set bit and return old value * test_and_clear_bit(bit, addr) Clear bit and return old value * test_and_change_bit(bit, addr) Change bit and return old value * find_first_zero_bit(addr, nbits) Position first zero bit in *addr * find_first_bit(addr, nbits) Position first set bit in *addr * find_next_zero_bit(addr, nbits, bit) Position next zero bit in *addr >= bit * find_next_bit(addr, nbits, bit) Position next set bit in *addr >= bit */ Paolo