diff options
| author | Denis Plotnikov <dplotnikov@virtuozzo.com> | 2019-12-20 17:09:04 +0300 |
|---|---|---|
| committer | Michael S. Tsirkin <mst@redhat.com> | 2020-01-06 12:04:43 -0500 |
| commit | 1bf8a989a566b2ba41c197004ec2a02562a766a4 (patch) | |
| tree | dcdec6a1c9fd7ad5713522ca30b3011d8310e00d /hw/scsi/virtio-scsi.c | |
| parent | d940208cbbbecd52bb6bac539c5e486bcc07abba (diff) | |
virtio: make seg_max virtqueue size dependent
Before the patch, seg_max parameter was immutable and hardcoded
to 126 (128 - 2) without respect to queue size. This has two negative effects:
1. when queue size is < 128, we have Virtio 1.1 specfication violation:
(2.6.5.3.1 Driver Requirements) seq_max must be <= queue_size.
This violation affects the old Linux guests (ver < 4.14). These guests
crash on these queue_size setups.
2. when queue_size > 128, as was pointed out by Denis Lunev <den@virtuozzo.com>,
seg_max restrics guest's block request length which affects guests'
performance making them issues more block request than needed.
https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html
To mitigate this two effects, the patch adds the property adjusting seg_max
to queue size automaticaly. Since seg_max is a guest visible parameter,
the property is machine type managable and allows to choose between
old (seg_max = 126 always) and new (seg_max = queue_size - 2) behaviors.
Not to change the behavior of the older VMs, prevent setting the default
seg_max_adjust value for older machine types.
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Denis Plotnikov <dplotnikov@virtuozzo.com>
Message-Id: <20191220140905.1718-2-dplotnikov@virtuozzo.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Diffstat (limited to 'hw/scsi/virtio-scsi.c')
| -rw-r--r-- | hw/scsi/virtio-scsi.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c index f080545f48..4bc73a370e 100644 --- a/hw/scsi/virtio-scsi.c +++ b/hw/scsi/virtio-scsi.c @@ -659,7 +659,8 @@ static void virtio_scsi_get_config(VirtIODevice *vdev, VirtIOSCSICommon *s = VIRTIO_SCSI_COMMON(vdev); virtio_stl_p(vdev, &scsiconf->num_queues, s->conf.num_queues); - virtio_stl_p(vdev, &scsiconf->seg_max, 128 - 2); + virtio_stl_p(vdev, &scsiconf->seg_max, + s->conf.seg_max_adjust ? s->conf.virtqueue_size - 2 : 128 - 2); virtio_stl_p(vdev, &scsiconf->max_sectors, s->conf.max_sectors); virtio_stl_p(vdev, &scsiconf->cmd_per_lun, s->conf.cmd_per_lun); virtio_stl_p(vdev, &scsiconf->event_info_size, sizeof(VirtIOSCSIEvent)); @@ -898,6 +899,11 @@ void virtio_scsi_common_realize(DeviceState *dev, virtio_cleanup(vdev); return; } + if (s->conf.virtqueue_size <= 2) { + error_setg(errp, "invalid virtqueue_size property (= %" PRIu32 "), " + "must be > 2", s->conf.virtqueue_size); + return; + } s->cmd_vqs = g_new0(VirtQueue *, s->conf.num_queues); s->sense_size = VIRTIO_SCSI_SENSE_DEFAULT_SIZE; s->cdb_size = VIRTIO_SCSI_CDB_DEFAULT_SIZE; @@ -954,6 +960,8 @@ static Property virtio_scsi_properties[] = { DEFINE_PROP_UINT32("num_queues", VirtIOSCSI, parent_obj.conf.num_queues, 1), DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSI, parent_obj.conf.virtqueue_size, 128), + DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSI, + parent_obj.conf.seg_max_adjust, true), DEFINE_PROP_UINT32("max_sectors", VirtIOSCSI, parent_obj.conf.max_sectors, 0xFFFF), DEFINE_PROP_UINT32("cmd_per_lun", VirtIOSCSI, parent_obj.conf.cmd_per_lun, |