Re: [Xen-devel] [PATCH MINI-OS] xenbus: notify the other end when necessary

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-10-26 at 09:47 +0000, Wei Liu wrote:
> The xenbus thread didn't send notification to other end when it expected
> more data or consumed responses, which led to stalling the ring from
> time to time.
> 
> This is the culprit that guest was less responsive when using stubdom
> because the device model was stalled.
> 
> Fix this by sending notification to the other end at the right places.

Could any of this code benefit from using the various macros in ring.h
which produce or consume entries on the ring and return a _notify bit?

> 
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
> Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>
> 
> With this path I can migrate a guest with stubdom a few thousand times
> without any issue, while before I could easily trigger time out
> within a few iterations. This should make OSSTest stubdom test case more
> reliable.
> 
> Ian J, this is a patch suitable for backporting to 4.6. It's good time
> to branch mini-os now.
> ---
>  xenbus/xenbus.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/xenbus/xenbus.c b/xenbus/xenbus.c
> index 4613ed6..7451161 100644
> --- a/xenbus/xenbus.c
> +++ b/xenbus/xenbus.c
> @@ -205,8 +205,10 @@ static void xenbus_thread_func(void *ign)
>              prod = xenstore_buf->rsp_prod;
>              DEBUG("Rsp_cons %d, rsp_prod %d.\n", xenstore_buf->rsp_cons,
>                      xenstore_buf->rsp_prod);
> -            if (xenstore_buf->rsp_prod - xenstore_buf->rsp_cons <
> sizeof(msg))
> +            if (xenstore_buf->rsp_prod - xenstore_buf->rsp_cons <
> sizeof(msg)) {
> +                notify_remote_via_evtchn(start_info.store_evtchn);
>                  break;
> +            }
>              rmb();
>              memcpy_from_ring(xenstore_buf->rsp,
>                      &msg,
> @@ -217,8 +219,10 @@ static void xenbus_thread_func(void *ign)
>                      xenstore_buf->rsp_prod - xenstore_buf->rsp_cons,
>                      msg.req_id);
>              if (xenstore_buf->rsp_prod - xenstore_buf->rsp_cons <
> -                    sizeof(msg) + msg.len)
> +                    sizeof(msg) + msg.len) {
> +                notify_remote_via_evtchn(start_info.store_evtchn);
>                  break;
> +            }
>  
>              DEBUG("Message is good.\n");
>  
> @@ -265,6 +269,9 @@ static void xenbus_thread_func(void *ign)
>                  xenstore_buf->rsp_cons += msg.len + sizeof(msg);
>                  wake_up(&req_info[msg.req_id].waitq);
>              }
> +
> +            wmb();
> +            notify_remote_via_evtchn(start_info.store_evtchn);
>          }
>      }
>  }

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