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/vhost-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/vhost-scsi.c')
| -rw-r--r-- | hw/scsi/vhost-scsi.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/hw/scsi/vhost-scsi.c b/hw/scsi/vhost-scsi.c index c693fc748a..26f710d3ec 100644 --- a/hw/scsi/vhost-scsi.c +++ b/hw/scsi/vhost-scsi.c @@ -275,6 +275,8 @@ static Property vhost_scsi_properties[] = { DEFINE_PROP_UINT32("num_queues", VirtIOSCSICommon, conf.num_queues, 1), DEFINE_PROP_UINT32("virtqueue_size", VirtIOSCSICommon, conf.virtqueue_size, 128), + DEFINE_PROP_BOOL("seg_max_adjust", VirtIOSCSICommon, conf.seg_max_adjust, + true), DEFINE_PROP_UINT32("max_sectors", VirtIOSCSICommon, conf.max_sectors, 0xFFFF), DEFINE_PROP_UINT32("cmd_per_lun", VirtIOSCSICommon, conf.cmd_per_lun, 128), |