Commit 392808b4 authored by Stefan Hajnoczi's avatar Stefan Hajnoczi
Browse files

virtio-blk: add x-data-plane=on|off performance feature 



The virtio-blk-data-plane feature is easy to integrate into
hw/virtio-blk.c.  The data plane can be started and stopped similar to
vhost-net.

Users can take advantage of the virtio-blk-data-plane feature using the
new -device virtio-blk-pci,x-data-plane=on property.

The x-data-plane name was chosen because at this stage the feature is
experimental and likely to see changes in the future.

If the VM configuration does not support virtio-blk-data-plane an error
message is printed.  Although we could fall back to regular virtio-blk,
I prefer the explicit approach since it prompts the user to fix their
configuration if they want the performance benefit of
virtio-blk-data-plane.

Limitations:
 * Only format=raw is supported
 * Live migration is not supported
 * Block jobs, hot unplug, and other operations fail with -EBUSY
 * I/O throttling limits are ignored
 * Only Linux hosts are supported due to Linux AIO usage

Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent e72f66a0

hw/virtio-blk.c

+43 −1
Original line number Diff line number Diff line
@@ -17,6 +17,9 @@ 
#include "hw/block-common.h"

#include "sysemu/blockdev.h"

#include "virtio-blk.h"

#ifdef CONFIG_VIRTIO_BLK_DATA_PLANE

#include "hw/dataplane/virtio-blk.h"

#endif

#include "scsi-defs.h"

#ifdef __linux__

# include <scsi/sg.h>
@@ -33,6 +36,9 @@ typedef struct VirtIOBlock 
    VirtIOBlkConf *blk;

    unsigned short sector_mask;

    DeviceState *qdev;

#ifdef CONFIG_VIRTIO_BLK_DATA_PLANE

    VirtIOBlockDataPlane *dataplane;

#endif

} VirtIOBlock;



static VirtIOBlock *to_virtio_blk(VirtIODevice *vdev)
@@ -407,6 +413,16 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq) 
        .num_writes = 0,

    };



#ifdef CONFIG_VIRTIO_BLK_DATA_PLANE

    /* Some guests kick before setting VIRTIO_CONFIG_S_DRIVER_OK so start

     * dataplane here instead of waiting for .set_status().

     */

    if (s->dataplane) {

        virtio_blk_data_plane_start(s->dataplane);

        return;

    }

#endif



    while ((req = virtio_blk_get_request(s))) {

        virtio_blk_handle_request(req, &mrb);

    }
@@ -446,8 +462,9 @@ static void virtio_blk_dma_restart_cb(void *opaque, int running, 
{

    VirtIOBlock *s = opaque;



    if (!running)

    if (!running) {

        return;

    }



    if (!s->bh) {

        s->bh = qemu_bh_new(virtio_blk_dma_restart_bh, s);
@@ -457,6 +474,14 @@ static void virtio_blk_dma_restart_cb(void *opaque, int running, 


static void virtio_blk_reset(VirtIODevice *vdev)

{

#ifdef CONFIG_VIRTIO_BLK_DATA_PLANE

    VirtIOBlock *s = to_virtio_blk(vdev);



    if (s->dataplane) {

        virtio_blk_data_plane_stop(s->dataplane);

    }

#endif



    /*

     * This should cancel pending requests, but can't do nicely until there

     * are per-device request lists.
@@ -541,6 +566,12 @@ static void virtio_blk_set_status(VirtIODevice *vdev, uint8_t status) 
    VirtIOBlock *s = to_virtio_blk(vdev);

    uint32_t features;



#ifdef CONFIG_VIRTIO_BLK_DATA_PLANE

    if (s->dataplane && !(status & VIRTIO_CONFIG_S_DRIVER)) {

        virtio_blk_data_plane_stop(s->dataplane);

    }

#endif



    if (!(status & VIRTIO_CONFIG_S_DRIVER_OK)) {

        return;

    }
@@ -638,6 +669,12 @@ VirtIODevice *virtio_blk_init(DeviceState *dev, VirtIOBlkConf *blk) 
    s->sector_mask = (s->conf->logical_block_size / BDRV_SECTOR_SIZE) - 1;



    s->vq = virtio_add_queue(&s->vdev, 128, virtio_blk_handle_output);

#ifdef CONFIG_VIRTIO_BLK_DATA_PLANE

    if (!virtio_blk_data_plane_create(&s->vdev, blk, &s->dataplane)) {

        virtio_cleanup(&s->vdev);

        return NULL;

    }

#endif



    qemu_add_vm_change_state_handler(virtio_blk_dma_restart_cb, s);

    s->qdev = dev;
@@ -655,6 +692,11 @@ VirtIODevice *virtio_blk_init(DeviceState *dev, VirtIOBlkConf *blk) 
void virtio_blk_exit(VirtIODevice *vdev)

{

    VirtIOBlock *s = to_virtio_blk(vdev);



#ifdef CONFIG_VIRTIO_BLK_DATA_PLANE

    virtio_blk_data_plane_destroy(s->dataplane);

    s->dataplane = NULL;

#endif

    unregister_savevm(s->qdev, "virtio-blk", s);

    blockdev_mark_auto_del(s->bs);

    virtio_cleanup(vdev);

hw/virtio-pci.c

+3 −0
Original line number Diff line number Diff line
@@ -896,6 +896,9 @@ static Property virtio_blk_properties[] = { 
#endif

    DEFINE_PROP_BIT("config-wce", VirtIOPCIProxy, blk.config_wce, 0, true),

    DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags, VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),

#ifdef CONFIG_VIRTIO_BLK_DATA_PLANE

    DEFINE_PROP_BIT("x-data-plane", VirtIOPCIProxy, blk.data_plane, 0, false),

#endif

    DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 2),

    DEFINE_VIRTIO_BLK_FEATURES(VirtIOPCIProxy, host_features),

    DEFINE_PROP_END_OF_LIST(),