On Mon, Feb 10, 2020 at 06:34:15PM +0300, Denis Plotnikov wrote: > > > On 09.02.2020 10:49, Michael S. Tsirkin wrote: > > On Fri, Feb 07, 2020 at 11:48:05AM +0300, Denis Plotnikov wrote: > > > > > > On 05.02.2020 14:19, Stefan Hajnoczi wrote: > > > > On Tue, Feb 04, 2020 at 12:59:04PM +0300, Denis Plotnikov wrote: > > > > > On 30.01.2020 17:58, Stefan Hajnoczi wrote: > > > > > > On Wed, Jan 29, 2020 at 05:07:00PM +0300, Denis Plotnikov wrote: > > > > > > > The goal is to reduce the amount of requests issued by a guest on > > > > > > > 1M reads/writes. This rises the performance up to 4% on that kind > > > > > > > of > > > > > > > disk access pattern. > > > > > > > > > > > > > > The maximum chunk size to be used for the guest disk accessing is > > > > > > > limited with seg_max parameter, which represents the max amount of > > > > > > > pices in the scatter-geather list in one guest disk request. > > > > > > > > > > > > > > Since seg_max is virqueue_size dependent, increasing the virtqueue > > > > > > > size increases seg_max, which, in turn, increases the maximum size > > > > > > > of data to be read/write from guest disk. > > > > > > > > > > > > > > More details in the original problem statment: > > > > > > > https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html > > > > > > > > > > > > > > Suggested-by: Denis V. Lunev <d...@openvz.org> > > > > > > > Signed-off-by: Denis Plotnikov <dplotni...@virtuozzo.com> > > > > > > > --- > > > > > > > hw/core/machine.c | 3 +++ > > > > > > > include/hw/virtio/virtio.h | 2 +- > > > > > > > 2 files changed, 4 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > diff --git a/hw/core/machine.c b/hw/core/machine.c > > > > > > > index 3e288bfceb..8bc401d8b7 100644 > > > > > > > --- a/hw/core/machine.c > > > > > > > +++ b/hw/core/machine.c > > > > > > > @@ -28,6 +28,9 @@ > > > > > > > #include "hw/mem/nvdimm.h" > > > > > > > GlobalProperty hw_compat_4_2[] = { > > > > > > > + { "virtio-blk-device", "queue-size", "128"}, > > > > > > > + { "virtio-scsi-device", "virtqueue_size", "128"}, > > > > > > > + { "vhost-blk-device", "virtqueue_size", "128"}, > > > > > > vhost-blk-device?! Who has this? It's not in qemu.git so please > > > > > > omit > > > > > > this line. ;-) > > > > > So in this case the line: > > > > > > > > > > { "vhost-blk-device", "seg_max_adjust", "off"}, > > > > > > > > > > introduced by my patch: > > > > > > > > > > commit 1bf8a989a566b2ba41c197004ec2a02562a766a4 > > > > > Author: Denis Plotnikov <dplotni...@virtuozzo.com> > > > > > Date: Fri Dec 20 17:09:04 2019 +0300 > > > > > > > > > > virtio: make seg_max virtqueue size dependent > > > > > > > > > > is also wrong. It should be: > > > > > > > > > > { "vhost-scsi-device", "seg_max_adjust", "off"}, > > > > > > > > > > Am I right? > > > > It's just called "vhost-scsi": > > > > > > > > include/hw/virtio/vhost-scsi.h:#define TYPE_VHOST_SCSI "vhost-scsi" > > > > > > > > > > On the other hand, do you want to do this for the vhost-user-blk, > > > > > > vhost-user-scsi, and vhost-scsi devices that exist in qemu.git? > > > > > > Those > > > > > > devices would benefit from better performance too. > > > After thinking about that for a while, I think we shouldn't extend queue > > > sizes for vhost-user-blk, vhost-user-scsi and vhost-scsi. > > > This is because increasing the queue sizes seems to be just useless for > > > them: the all thing is about increasing the queue sizes for increasing > > > seg_max (it limits the max block query size from the guest). For > > > virtio-blk-device and virtio-scsi-device it makes sense, since they have > > > seg-max-adjust property which, if true, sets seg_max to virtqueue_size-2. > > > vhost-scsi also have this property but it seems the property just doesn't > > > affect anything (remove it?). > > > Also vhost-user-blk, vhost-user-scsi and vhost-scsi don't do any seg_max > > > settings. If I understand correctly, their backends are ment to be > > > responsible for doing that. > > The queue size is set by qemu IIRC. > > > > > So, what about changing the queue sizes just for virtio-blk-device and > > > virtio-scsi-device? > > > > Hmm that would break ability to migrate between userspace and vhost > > backends, would it not? > I'm not sure I've understood what you meant. > Just for the record, I was going to change virtqueue-size for > virtio-blk-device and virtio-scsi-device
If virtqueue size is different between virtio-blk-device and vhost-user-blk then one can not migrate the former to the later. > since they can adjust seg_max to > the specified queue size and I don't want to touch vhost-s and vhost-user-s > since they don't have adjustable seg_max for now. > > Denis If I just grep seg_max_adjust I see them for vhost devices too. Is that code ineffective somehow? What's it doing then? > > > > > > > Denis > > > > > > > > It seems to be so. We also have the test checking those settings: > > > > > tests/acceptance/virtio_seg_max_adjust.py > > > > > For now it checks virtio-scsi-pci and virtio-blk-pci. > > > > > I'm going to extend it for the virtqueue size checking. > > > > > If I change vhost-user-blk, vhost-user-scsi and vhost-scsi it's worth > > > > > to check those devices too. But I don't know how to form a command > > > > > line > > > > > for that 3 devices since they should involve some third party > > > > > components as > > > > > backends (kernel modules, DPDK, etc.) and they seems to be not > > > > > available in > > > > > the > > > > > qemu git. > > > > > Is there any way to do it with some qit.qemu available stubs or > > > > > something > > > > > else? > > > > > If so, could you please point out the proper way to do it? > > > > qemu.git has contrib/vhost-user-blk/ and contrib/vhost-user-scsi/ if > > > > you need to test those vhost-user devices without external dependencies. > > > > > > > > Stefan
