From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1M74d5-0006mL-Hl for qemu-devel@nongnu.org; Thu, 21 May 2009 05:31:59 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1M74cz-0006hW-Lg for qemu-devel@nongnu.org; Thu, 21 May 2009 05:31:57 -0400 Received: from [199.232.76.173] (port=47651 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1M74cz-0006hS-D8 for qemu-devel@nongnu.org; Thu, 21 May 2009 05:31:53 -0400 Received: from mx2.redhat.com ([66.187.237.31]:47936) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1M74cy-0000B9-TX for qemu-devel@nongnu.org; Thu, 21 May 2009 05:31:53 -0400 Received: from int-mx2.corp.redhat.com (int-mx2.corp.redhat.com [172.16.27.26]) by mx2.redhat.com (8.13.8/8.13.8) with ESMTP id n4L9Vp1E015587 for ; Thu, 21 May 2009 05:31:51 -0400 Message-ID: <4A151F9F.7050208@redhat.com> Date: Thu, 21 May 2009 12:32:15 +0300 From: Dor Laor MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH] migrate.c: migrate_fd_put_buffer: Do not busyloop: stop writing if EWOULDBLOCK References: <1242731333-1526-1-git-send-email-uril@redhat.com> In-Reply-To: <1242731333-1526-1-git-send-email-uril@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Reply-To: dlaor@redhat.com List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Uri Lublin Cc: qemu-devel@nongnu.org Uri Lublin wrote: > The migration code is non-blocking, designed for live migration. > > Practically migrate_fd_put_buffer busy-loops trying to write, as > on many machines EWOULDBLOCK==EAGAIN (look in include/asm-generic/errno.h). > > Signed-off-by: Uri Lublin > --- > migration.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/migration.c b/migration.c > index 859d945..ca397fa 100644 > --- a/migration.c > +++ b/migration.c > @@ -176,7 +176,7 @@ ssize_t migrate_fd_put_buffer(void *opaque, const void *data, size_t size) > > do { > ret = s->write(s, data, size); > - } while (ret == -1 && ((s->get_error(s)) == EINTR || (s->get_error(s)) == EWOULDBLOCK)); > + } while (ret == -1 && ((s->get_error(s)) == EINTR)); > > if (ret == -1) > ret = -(s->get_error(s)); > There is additional stuff that needs to test EWOULDBLOCK in further locations in the code. Otherwise migration will fail. commit 2d875410cb168fa728dcde96885a3e4ddfd0bb58 Author: Dor Laor Date: Thu May 21 12:29:39 2009 +0300 The migration code is non-blocking, designed for live migration. Practically migrate_fd_put_buffer busy-loops trying to write, as on many machines EWOULDBLOCK==EAGAIN (look in include/asm-generic/errno.h). Based on Uri Lublin's patch. Signed-off-by: Dor Laor diff --git a/qemu/buffered_file.c b/qemu/buffered_file.c index be5baea..34cde6e 100644 --- a/qemu/buffered_file.c +++ b/qemu/buffered_file.c @@ -86,7 +86,7 @@ static void buffered_flush(QEMUFileBuffered *s) ret = s->put_buffer(s->opaque, s->buffer + offset, s->buffer_size - offset); - if (ret == -EAGAIN) { + if (ret == -EAGAIN || ret == -EWOULDBLOCK) { dprintf("backend not ready, freezing\n"); s->freeze_output = 1; break; @@ -132,7 +132,7 @@ static int buffered_put_buffer(void *opaque, const uint8_t *buf, int64_t pos, in } ret = s->put_buffer(s->opaque, buf + offset, size - offset); - if (ret == -EAGAIN) { + if (ret == -EAGAIN || ret ==-EWOULDBLOCK) { dprintf("backend not ready, freezing\n"); s->freeze_output = 1; break; diff --git a/qemu/migration.c b/qemu/migration.c index 85757c5..8846eee 100644 --- a/qemu/migration.c +++ b/qemu/migration.c @@ -174,7 +174,7 @@ ssize_t migrate_fd_put_buffer(void *opaque, const void *data, size_t size) if (ret == -1) ret = -(s->get_error(s)); - if (ret == -EAGAIN) + if (ret == -EAGAIN || ret == -EWOULDBLOCK) qemu_set_fd_handler2(s->fd, NULL, NULL, migrate_fd_put_notify, s); return ret;