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authorDenis Plotnikov <dplotnikov@virtuozzo.com>2019-12-20 17:09:04 +0300
committerMichael S. Tsirkin <mst@redhat.com>2020-01-06 12:04:43 -0500
commit1bf8a989a566b2ba41c197004ec2a02562a766a4 (patch)
treedcdec6a1c9fd7ad5713522ca30b3011d8310e00d /include/hw
parentd940208cbbbecd52bb6bac539c5e486bcc07abba (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')
-rw-r--r--include/hw/virtio/virtio-blk.h1
-rw-r--r--include/hw/virtio/virtio-scsi.h1
2 files changed, 2 insertions, 0 deletions
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index 9c19f5b634..1e62f869b2 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -38,6 +38,7 @@ struct VirtIOBlkConf
uint32_t request_merging;
uint16_t num_queues;
uint16_t queue_size;
+ bool seg_max_adjust;
uint32_t max_discard_sectors;
uint32_t max_write_zeroes_sectors;
bool x_enable_wce_if_config_wce;
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