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| 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/block | |
| parent | d940208cbbbecd52bb6bac539c5e486bcc07abba (diff) | |
| download | qemu-1bf8a989a566b2ba41c197004ec2a02562a766a4.zip | |
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/block')
| -rw-r--r-- | hw/block/virtio-blk.c | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c index b12157b5eb..9bee514c4e 100644 --- a/hw/block/virtio-blk.c +++ b/hw/block/virtio-blk.c @@ -913,7 +913,8 @@ static void virtio_blk_update_config(VirtIODevice *vdev, uint8_t *config) blk_get_geometry(s->blk, &capacity); memset(&blkcfg, 0, sizeof(blkcfg)); virtio_stq_p(vdev, &blkcfg.capacity, capacity); - virtio_stl_p(vdev, &blkcfg.seg_max, 128 - 2); + virtio_stl_p(vdev, &blkcfg.seg_max, + s->conf.seg_max_adjust ? s->conf.queue_size - 2 : 128 - 2); virtio_stw_p(vdev, &blkcfg.geometry.cylinders, conf->cyls); virtio_stl_p(vdev, &blkcfg.blk_size, blk_size); virtio_stw_p(vdev, &blkcfg.min_io_size, conf->min_io_size / blk_size); @@ -1138,6 +1139,11 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp) error_setg(errp, "num-queues property must be larger than 0"); return; } + if (conf->queue_size <= 2) { + error_setg(errp, "invalid queue-size property (%" PRIu16 "), " + "must be > 2", conf->queue_size); + return; + } if (!is_power_of_2(conf->queue_size) || conf->queue_size > VIRTQUEUE_MAX_SIZE) { error_setg(errp, "invalid queue-size property (%" PRIu16 "), " @@ -1267,6 +1273,7 @@ static Property virtio_blk_properties[] = { true), DEFINE_PROP_UINT16("num-queues", VirtIOBlock, conf.num_queues, 1), DEFINE_PROP_UINT16("queue-size", VirtIOBlock, conf.queue_size, 128), + DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true), DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD, IOThread *), DEFINE_PROP_BIT64("discard", VirtIOBlock, host_features, |