From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58637) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dVyXC-0007MD-1w for qemu-devel@nongnu.org; Fri, 14 Jul 2017 07:13:23 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dVyX8-0007M4-Si for qemu-devel@nongnu.org; Fri, 14 Jul 2017 07:13:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48890) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dVyX8-0007Lf-JM for qemu-devel@nongnu.org; Fri, 14 Jul 2017 07:13:18 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6D6AFC0587E6 for ; Fri, 14 Jul 2017 11:13:17 +0000 (UTC) Date: Fri, 14 Jul 2017 12:13:11 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20170714111311.GB2091@work-vm> References: <20170713115649.11853-1-dgilbert@redhat.com> <20170713115649.11853-4-dgilbert@redhat.com> <20170714033619.GG27284@pxdev.xzpeter.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170714033619.GG27284@pxdev.xzpeter.org> Subject: Re: [Qemu-devel] [PATCH v2 3/5] migration/rdma: Allow cancelling while waiting for wrid List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Xu Cc: qemu-devel@nongnu.org, quintela@redhat.com, lvivier@redhat.com * Peter Xu (peterx@redhat.com) wrote: > On Thu, Jul 13, 2017 at 12:56:47PM +0100, Dr. David Alan Gilbert (git) wrote: > > From: "Dr. David Alan Gilbert" > > > > When waiting for a WRID, if the other side dies we end up waiting > > for ever with no way to cancel the migration. > > Cure this by poll()ing the fd first with a timeout and checking > > error flags and migration state. > > > > Signed-off-by: Dr. David Alan Gilbert > > --- > > migration/rdma.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++------ > > 1 file changed, 46 insertions(+), 6 deletions(-) > > > > diff --git a/migration/rdma.c b/migration/rdma.c > > index 6111e10c70..30f5542b49 100644 > > --- a/migration/rdma.c > > +++ b/migration/rdma.c > > @@ -1466,6 +1466,50 @@ static uint64_t qemu_rdma_poll(RDMAContext *rdma, uint64_t *wr_id_out, > > return 0; > > } > > > > +/* Wait for activity on the completion channel. > > + * Returns 0 on success, none-0 on error. > > + */ > > +static int qemu_rdma_wait_comp_channel(RDMAContext *rdma) > > +{ > > + /* > > + * Coroutine doesn't start until migration_fd_process_incoming() > > + * so don't yield unless we know we're running inside of a coroutine. > > + */ > > + if (rdma->migration_started_on_destination) { > > + yield_until_fd_readable(rdma->comp_channel->fd); > > + } else { > > + /* This is the source side, we're in a separate thread > > + * or destination prior to migration_fd_process_incoming() > > + * we can't yield; so we have to poll the fd. > > + * But we need to be able to handle 'cancel' or an error > > + * without hanging forever. > > + */ > > + while (!rdma->error_state && !rdma->received_error) { > > + GPollFD pfds[1]; > > + pfds[0].fd = rdma->comp_channel->fd; > > + pfds[0].events = G_IO_IN | G_IO_HUP | G_IO_ERR; > > + /* 0.1s timeout, should be fine for a 'cancel' */ > > + switch (qemu_poll_ns(pfds, 1, 100 * 1000 * 1000)) { > > + case 1: /* fd active */ > > + return 0; > > + > > + case 0: /* Timeout, go around again */ > > + break; > > + > > + default: /* Error of some type */ > > + return -1; > > + } > > + > > + if (migrate_get_current()->state == MIGRATION_STATUS_CANCELLING) { > > + /* Bail out and let the cancellation happen */ > > + return -EPIPE; > > + } > > + } > > + } > > + > > + return rdma->error_state || rdma->received_error; > > Just to note that this operation will return either 0 or 1, but not > anything <0 (most RDMA codes are using <0 as error, and error_state > should be <= 0 always iiuc). > > But as the comment for this function, it's fine. It's interesting in that 'error_state' is a -ve error code, where as received_error is just a boolean; I've changed this to: if (rdma->received->error) { return -EPIPE; } return rdma->error_state; to make it a bit more consistent. > > +} > > + > > /* > > * Block until the next work request has completed. > > * > > @@ -1513,12 +1557,8 @@ static int qemu_rdma_block_for_wrid(RDMAContext *rdma, int wrid_requested, > > } > > > > while (1) { > > - /* > > - * Coroutine doesn't start until migration_fd_process_incoming() > > - * so don't yield unless we know we're running inside of a coroutine. > > - */ > > - if (rdma->migration_started_on_destination) { > > - yield_until_fd_readable(rdma->comp_channel->fd); > > + if (qemu_rdma_wait_comp_channel(rdma)) { > > Do we want something like: > > ret = -EIO; > > Here? Or capture the return code of qemu_rdma_wait_comp_channel() (but > then we need to make sure its return code is <0)? > > I guess "ret" is still zero, and it means this function will return > with zero as well even timed out? But rdma->error_state is set if wait_comp_channel fails; (actually it wasn't in one case, where the poll fails, I've just fixed that and will repost). Dave > Thanks, > > -- > Peter Xu -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK