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Re: [Qemu-devel] [PATCH] virtio: Report real progress in VQ aio poll han


From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH] virtio: Report real progress in VQ aio poll handler
Date: Thu, 9 Feb 2017 15:58:31 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1


On 09/02/2017 09:40, Fam Zheng wrote:
> In virtio_queue_host_notifier_aio_poll, not all "!virtio_queue_empty()"
> cases are making true progress.
> 
> Currently the offending one is virtio-scsi event queue, whose handler
> does nothing if no event is pending. As a result aio_poll() will spin on
> the "non-empty" VQ and take 100% host CPU.
> 
> Fix this by reporting actual progress from virtio queue aio handlers.
> 
> Reported-by: Ed Swierk <address@hidden>
> Signed-off-by: Fam Zheng <address@hidden>

Looks good.  The alternative is to disable altogether the event queue
handler unless events_dropped is true.

Paolo

> ---
>  hw/block/dataplane/virtio-blk.c |  4 ++--
>  hw/block/virtio-blk.c           | 12 ++++++++++--
>  hw/scsi/virtio-scsi-dataplane.c | 14 +++++++-------
>  hw/scsi/virtio-scsi.c           | 14 +++++++++++---
>  hw/virtio/virtio.c              | 15 +++++++++------
>  include/hw/virtio/virtio-blk.h  |  2 +-
>  include/hw/virtio/virtio-scsi.h |  6 +++---
>  include/hw/virtio/virtio.h      |  4 ++--
>  8 files changed, 45 insertions(+), 26 deletions(-)
> 
> diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
> index d1f9f63..5556f0e 100644
> --- a/hw/block/dataplane/virtio-blk.c
> +++ b/hw/block/dataplane/virtio-blk.c
> @@ -147,7 +147,7 @@ void virtio_blk_data_plane_destroy(VirtIOBlockDataPlane 
> *s)
>      g_free(s);
>  }
>  
> -static void virtio_blk_data_plane_handle_output(VirtIODevice *vdev,
> +static bool virtio_blk_data_plane_handle_output(VirtIODevice *vdev,
>                                                  VirtQueue *vq)
>  {
>      VirtIOBlock *s = (VirtIOBlock *)vdev;
> @@ -155,7 +155,7 @@ static void 
> virtio_blk_data_plane_handle_output(VirtIODevice *vdev,
>      assert(s->dataplane);
>      assert(s->dataplane_started);
>  
> -    virtio_blk_handle_vq(s, vq);
> +    return virtio_blk_handle_vq(s, vq);
>  }
>  
>  /* Context: QEMU global mutex held */
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 702eda8..baaa195 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -581,10 +581,11 @@ static int virtio_blk_handle_request(VirtIOBlockReq 
> *req, MultiReqBuffer *mrb)
>      return 0;
>  }
>  
> -void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq)
> +bool virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq)
>  {
>      VirtIOBlockReq *req;
>      MultiReqBuffer mrb = {};
> +    bool progress = false;
>  
>      blk_io_plug(s->blk);
>  
> @@ -592,6 +593,7 @@ void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq)
>          virtio_queue_set_notification(vq, 0);
>  
>          while ((req = virtio_blk_get_request(s, vq))) {
> +            progress = true;
>              if (virtio_blk_handle_request(req, &mrb)) {
>                  virtqueue_detach_element(req->vq, &req->elem, 0);
>                  virtio_blk_free_request(req);
> @@ -607,6 +609,12 @@ void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq)
>      }
>  
>      blk_io_unplug(s->blk);
> +    return progress;
> +}
> +
> +static void virtio_blk_handle_output_do(VirtIOBlock *s, VirtQueue *vq)
> +{
> +    virtio_blk_handle_vq(s, vq);
>  }
>  
>  static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
> @@ -622,7 +630,7 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, 
> VirtQueue *vq)
>              return;
>          }
>      }
> -    virtio_blk_handle_vq(s, vq);
> +    virtio_blk_handle_output_do(s, vq);
>  }
>  
>  static void virtio_blk_dma_restart_bh(void *opaque)
> diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c
> index 6b8d0f0..74c95e0 100644
> --- a/hw/scsi/virtio-scsi-dataplane.c
> +++ b/hw/scsi/virtio-scsi-dataplane.c
> @@ -49,35 +49,35 @@ void virtio_scsi_dataplane_setup(VirtIOSCSI *s, Error 
> **errp)
>      }
>  }
>  
> -static void virtio_scsi_data_plane_handle_cmd(VirtIODevice *vdev,
> +static bool virtio_scsi_data_plane_handle_cmd(VirtIODevice *vdev,
>                                                VirtQueue *vq)
>  {
>      VirtIOSCSI *s = (VirtIOSCSI *)vdev;
>  
>      assert(s->ctx && s->dataplane_started);
> -    virtio_scsi_handle_cmd_vq(s, vq);
> +    return virtio_scsi_handle_cmd_vq(s, vq);
>  }
>  
> -static void virtio_scsi_data_plane_handle_ctrl(VirtIODevice *vdev,
> +static bool virtio_scsi_data_plane_handle_ctrl(VirtIODevice *vdev,
>                                                 VirtQueue *vq)
>  {
>      VirtIOSCSI *s = VIRTIO_SCSI(vdev);
>  
>      assert(s->ctx && s->dataplane_started);
> -    virtio_scsi_handle_ctrl_vq(s, vq);
> +    return virtio_scsi_handle_ctrl_vq(s, vq);
>  }
>  
> -static void virtio_scsi_data_plane_handle_event(VirtIODevice *vdev,
> +static bool virtio_scsi_data_plane_handle_event(VirtIODevice *vdev,
>                                                  VirtQueue *vq)
>  {
>      VirtIOSCSI *s = VIRTIO_SCSI(vdev);
>  
>      assert(s->ctx && s->dataplane_started);
> -    virtio_scsi_handle_event_vq(s, vq);
> +    return virtio_scsi_handle_event_vq(s, vq);
>  }
>  
>  static int virtio_scsi_vring_init(VirtIOSCSI *s, VirtQueue *vq, int n,
> -                                  void (*fn)(VirtIODevice *vdev, VirtQueue 
> *vq))
> +                                  VirtIOHandleAIOOutput fn)
>  {
>      BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s)));
>      int rc;
> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> index ce19eff..b01030b 100644
> --- a/hw/scsi/virtio-scsi.c
> +++ b/hw/scsi/virtio-scsi.c
> @@ -436,13 +436,16 @@ static inline void virtio_scsi_release(VirtIOSCSI *s)
>      }
>  }
>  
> -void virtio_scsi_handle_ctrl_vq(VirtIOSCSI *s, VirtQueue *vq)
> +bool virtio_scsi_handle_ctrl_vq(VirtIOSCSI *s, VirtQueue *vq)
>  {
>      VirtIOSCSIReq *req;
> +    bool progress = false;
>  
>      while ((req = virtio_scsi_pop_req(s, vq))) {
> +        progress = true;
>          virtio_scsi_handle_ctrl_req(s, req);
>      }
> +    return progress;
>  }
>  
>  static void virtio_scsi_handle_ctrl(VirtIODevice *vdev, VirtQueue *vq)
> @@ -591,10 +594,11 @@ static void 
> virtio_scsi_handle_cmd_req_submit(VirtIOSCSI *s, VirtIOSCSIReq *req)
>      scsi_req_unref(sreq);
>  }
>  
> -void virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue *vq)
> +bool virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue *vq)
>  {
>      VirtIOSCSIReq *req, *next;
>      int ret = 0;
> +    bool progress = false;
>  
>      QTAILQ_HEAD(, VirtIOSCSIReq) reqs = QTAILQ_HEAD_INITIALIZER(reqs);
>  
> @@ -602,6 +606,7 @@ void virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue 
> *vq)
>          virtio_queue_set_notification(vq, 0);
>  
>          while ((req = virtio_scsi_pop_req(s, vq))) {
> +            progress = true;
>              ret = virtio_scsi_handle_cmd_req_prepare(s, req);
>              if (!ret) {
>                  QTAILQ_INSERT_TAIL(&reqs, req, next);
> @@ -624,6 +629,7 @@ void virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue 
> *vq)
>      QTAILQ_FOREACH_SAFE(req, &reqs, next, next) {
>          virtio_scsi_handle_cmd_req_submit(s, req);
>      }
> +    return progress;
>  }
>  
>  static void virtio_scsi_handle_cmd(VirtIODevice *vdev, VirtQueue *vq)
> @@ -752,11 +758,13 @@ out:
>      virtio_scsi_release(s);
>  }
>  
> -void virtio_scsi_handle_event_vq(VirtIOSCSI *s, VirtQueue *vq)
> +bool virtio_scsi_handle_event_vq(VirtIOSCSI *s, VirtQueue *vq)
>  {
>      if (s->events_dropped) {
>          virtio_scsi_push_event(s, NULL, VIRTIO_SCSI_T_NO_EVENT, 0);
> +        return true;
>      }
> +    return false;
>  }
>  
>  static void virtio_scsi_handle_event(VirtIODevice *vdev, VirtQueue *vq)
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 6365706..2461c06 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -97,7 +97,7 @@ struct VirtQueue
>  
>      uint16_t vector;
>      VirtIOHandleOutput handle_output;
> -    VirtIOHandleOutput handle_aio_output;
> +    VirtIOHandleAIOOutput handle_aio_output;
>      VirtIODevice *vdev;
>      EventNotifier guest_notifier;
>      EventNotifier host_notifier;
> @@ -1287,14 +1287,16 @@ void virtio_queue_set_align(VirtIODevice *vdev, int 
> n, int align)
>      virtio_queue_update_rings(vdev, n);
>  }
>  
> -static void virtio_queue_notify_aio_vq(VirtQueue *vq)
> +static bool virtio_queue_notify_aio_vq(VirtQueue *vq)
>  {
>      if (vq->vring.desc && vq->handle_aio_output) {
>          VirtIODevice *vdev = vq->vdev;
>  
>          trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
> -        vq->handle_aio_output(vdev, vq);
> +        return vq->handle_aio_output(vdev, vq);
>      }
> +
> +    return false;
>  }
>  
>  static void virtio_queue_notify_vq(VirtQueue *vq)
> @@ -2125,16 +2127,17 @@ static bool virtio_queue_host_notifier_aio_poll(void 
> *opaque)
>  {
>      EventNotifier *n = opaque;
>      VirtQueue *vq = container_of(n, VirtQueue, host_notifier);
> +    bool progress;
>  
>      if (virtio_queue_empty(vq)) {
>          return false;
>      }
>  
> -    virtio_queue_notify_aio_vq(vq);
> +    progress = virtio_queue_notify_aio_vq(vq);
>  
>      /* In case the handler function re-enabled notifications */
>      virtio_queue_set_notification(vq, 0);
> -    return true;
> +    return progress;
>  }
>  
>  static void virtio_queue_host_notifier_aio_poll_end(EventNotifier *n)
> @@ -2146,7 +2149,7 @@ static void 
> virtio_queue_host_notifier_aio_poll_end(EventNotifier *n)
>  }
>  
>  void virtio_queue_aio_set_host_notifier_handler(VirtQueue *vq, AioContext 
> *ctx,
> -                                                VirtIOHandleOutput 
> handle_output)
> +                                                VirtIOHandleAIOOutput 
> handle_output)
>  {
>      if (handle_output) {
>          vq->handle_aio_output = handle_output;
> diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
> index 9734b4c..d3c8a6f 100644
> --- a/include/hw/virtio/virtio-blk.h
> +++ b/include/hw/virtio/virtio-blk.h
> @@ -80,6 +80,6 @@ typedef struct MultiReqBuffer {
>      bool is_write;
>  } MultiReqBuffer;
>  
> -void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq);
> +bool virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq);
>  
>  #endif
> diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h
> index 7375196..f536f77 100644
> --- a/include/hw/virtio/virtio-scsi.h
> +++ b/include/hw/virtio/virtio-scsi.h
> @@ -126,9 +126,9 @@ void virtio_scsi_common_realize(DeviceState *dev, Error 
> **errp,
>                                  VirtIOHandleOutput cmd);
>  
>  void virtio_scsi_common_unrealize(DeviceState *dev, Error **errp);
> -void virtio_scsi_handle_event_vq(VirtIOSCSI *s, VirtQueue *vq);
> -void virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue *vq);
> -void virtio_scsi_handle_ctrl_vq(VirtIOSCSI *s, VirtQueue *vq);
> +bool virtio_scsi_handle_event_vq(VirtIOSCSI *s, VirtQueue *vq);
> +bool virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue *vq);
> +bool virtio_scsi_handle_ctrl_vq(VirtIOSCSI *s, VirtQueue *vq);
>  void virtio_scsi_init_req(VirtIOSCSI *s, VirtQueue *vq, VirtIOSCSIReq *req);
>  void virtio_scsi_free_req(VirtIOSCSIReq *req);
>  void virtio_scsi_push_event(VirtIOSCSI *s, SCSIDevice *dev,
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index 525da24..0863a25 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -154,6 +154,7 @@ void virtio_error(VirtIODevice *vdev, const char *fmt, 
> ...) GCC_FMT_ATTR(2, 3);
>  void virtio_device_set_child_bus_name(VirtIODevice *vdev, char *bus_name);
>  
>  typedef void (*VirtIOHandleOutput)(VirtIODevice *, VirtQueue *);
> +typedef bool (*VirtIOHandleAIOOutput)(VirtIODevice *, VirtQueue *);
>  
>  VirtQueue *virtio_add_queue(VirtIODevice *vdev, int queue_size,
>                              VirtIOHandleOutput handle_output);
> @@ -284,8 +285,7 @@ bool virtio_device_ioeventfd_enabled(VirtIODevice *vdev);
>  EventNotifier *virtio_queue_get_host_notifier(VirtQueue *vq);
>  void virtio_queue_host_notifier_read(EventNotifier *n);
>  void virtio_queue_aio_set_host_notifier_handler(VirtQueue *vq, AioContext 
> *ctx,
> -                                                void (*fn)(VirtIODevice *,
> -                                                           VirtQueue *));
> +                                                VirtIOHandleAIOOutput 
> handle_output);
>  VirtQueue *virtio_vector_first_queue(VirtIODevice *vdev, uint16_t vector);
>  VirtQueue *virtio_vector_next_queue(VirtQueue *vq);
>  
> 



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