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 /include/hw/virtio/virtio-scsi.h | |
| 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 'include/hw/virtio/virtio-scsi.h')
| -rw-r--r-- | include/hw/virtio/virtio-scsi.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h index 122f7c4b6f..24e768909d 100644 --- a/include/hw/virtio/virtio-scsi.h +++ b/include/hw/virtio/virtio-scsi.h @@ -48,6 +48,7 @@ typedef struct virtio_scsi_config VirtIOSCSIConfig; struct VirtIOSCSIConf { uint32_t num_queues; uint32_t virtqueue_size; + bool seg_max_adjust; uint32_t max_sectors; uint32_t cmd_per_lun; #ifdef CONFIG_VHOST_SCSI |