From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54570) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fOasz-0008Np-HD for qemu-devel@nongnu.org; Thu, 31 May 2018 23:37:54 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fOasw-0001fI-E9 for qemu-devel@nongnu.org; Thu, 31 May 2018 23:37:53 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:38442 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fOasw-0001aI-9t for qemu-devel@nongnu.org; Thu, 31 May 2018 23:37:50 -0400 Date: Fri, 1 Jun 2018 11:37:39 +0800 From: Peter Xu Message-ID: <20180601033739.GF14867@xz-mi> References: <1524550428-27173-1-git-send-email-wei.w.wang@intel.com> <1524550428-27173-3-git-send-email-wei.w.wang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1524550428-27173-3-git-send-email-wei.w.wang@intel.com> Subject: Re: [Qemu-devel] [PATCH v7 2/5] migration: use bitmap_mutex in migration_bitmap_clear_dirty List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Wei Wang Cc: qemu-devel@nongnu.org, virtio-dev@lists.oasis-open.org, mst@redhat.com, quintela@redhat.com, dgilbert@redhat.com, yang.zhang.wz@gmail.com, quan.xu0@gmail.com, liliang.opensource@gmail.com, pbonzini@redhat.com, nilal@redhat.com On Tue, Apr 24, 2018 at 02:13:45PM +0800, Wei Wang wrote: > The bitmap mutex is used to synchronize threads to update the dirty > bitmap and the migration_dirty_pages counter. This patch makes > migration_bitmap_clear_dirty update the bitmap and counter under the > mutex. > > Signed-off-by: Wei Wang > CC: Dr. David Alan Gilbert > CC: Juan Quintela > CC: Michael S. Tsirkin > --- > migration/ram.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/migration/ram.c b/migration/ram.c > index 0e90efa..9a72b1a 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -795,11 +795,14 @@ static inline bool migration_bitmap_clear_dirty(RAMState *rs, > { > bool ret; > > + qemu_mutex_lock(&rs->bitmap_mutex); > ret = test_and_clear_bit(page, rb->bmap); > > if (ret) { > rs->migration_dirty_pages--; > } > + qemu_mutex_unlock(&rs->bitmap_mutex); > + > return ret; > } > > -- > 1.8.3.1 > > Do we need the lock after all? I see that we introduced this lock due to device hotplug at dd63169766 ("migration: extend migration_bitmap", 2015-07-07), however now we actually don't allow that to happen any more after commit b06424de62 ("migration: Disable hotplug/unplug during migration", 2017-04-21). I'm not sure whether it means that the lock is not needed now. If so, this patch seems to be unecessary. Regards, -- Peter Xu