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Re: [Qemu-devel] [PATCH v2 3/5] migration/rdma: Allow cancelling while w
From: |
Peter Xu |
Subject: |
Re: [Qemu-devel] [PATCH v2 3/5] migration/rdma: Allow cancelling while waiting for wrid |
Date: |
Fri, 14 Jul 2017 11:36:19 +0800 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Thu, Jul 13, 2017 at 12:56:47PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
>
> 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 <address@hidden>
> ---
> 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.
> +}
> +
> /*
> * 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?
Thanks,
--
Peter Xu
- [Qemu-devel] [PATCH v2 0/5] A bunch of RDMA fixes, Dr. David Alan Gilbert (git), 2017/07/13
- [Qemu-devel] [PATCH v2 1/5] migration/rdma: Fix race on source, Dr. David Alan Gilbert (git), 2017/07/13
- [Qemu-devel] [PATCH v2 2/5] migration: Close file on failed migration load, Dr. David Alan Gilbert (git), 2017/07/13
- [Qemu-devel] [PATCH v2 3/5] migration/rdma: Allow cancelling while waiting for wrid, Dr. David Alan Gilbert (git), 2017/07/13
- Re: [Qemu-devel] [PATCH v2 3/5] migration/rdma: Allow cancelling while waiting for wrid,
Peter Xu <=
- [Qemu-devel] [PATCH v2 4/5] migration/rdma: Safely convert control types, Dr. David Alan Gilbert (git), 2017/07/13
- [Qemu-devel] [PATCH v2 5/5] migration/rdma: Send error during cancelling, Dr. David Alan Gilbert (git), 2017/07/13