[PATCH v2 00/10] RFC: NVME MDEV

Maxim Levitsky
2019-05-02T11:49:27Z

Hi everyone!

In this patch series, I would like to introduce my take on the problem of doing
as fast as possible virtualization of storage with emphasis on low latency.

For more information for the inner working you can look at V1 of the submission
at
https://lkml.org/lkml/2019/3/19/458

*** Changes from V1 ***

* Some correctness fixes that slipped in the last minute,
Nothing major though, and all my attempt to crash this driver lately
were unsucessfull,
and it pretty much copes with anything I throw at it.

* Experemental block layer mode: In this mode, the mdev driver sends
the IO though the block layer (using bio_submit), and then polls for
the completions using the blk_poll. The last commit in the series adds this.
The performance overhead of this is about 2x of direct dedicated queue submission
though.

For this patch series, I would like to hear your opinion on the generic
block layer code, and to hear your opinion on the code as whole.

Please ignore the fact that code doesn't use nvme target code
(for instance it already have the generic block device code in io-cmd-bdev.c)
I will later switch to it, in next version of these patches, although,
I think that I should keep the option of using the direct, reserved IO queue
version too.

*** Performance results ***

Two tests were run, this time focusing only on latency and especially
on measuring the overhead of the translation.

I used the nvme-5.2 branch of http://git.infradead.org/nvme.git
which includes the small IO performance improvments which show a modest
perf increase in the generic block layer code path.

So the tests were:

** No interrupts test**

For that test, I used spdk's fio plugin as the test client. It itself uses
vfio to bind to the device, and then read/write from it using polling.
For tests that run in the guest, I used the virtual IOMMU, and run that spdk
test in the guest.

IOW, the tests were:

1. spdk in the host with fio
2. nvme-mdev in the host, spdk in the guest with fio
3. spdk in the host, spdk in the guest with fio

The fio (with the spdk plugin)was running at queue depth 1.
In addtion to that I added rdtsc based instrumentation to my mdev driver
to read the number of cycles it takes it to translate a command, and number
of cycles it takes it to poll for the response, and also number of cycles,
it takes to send the interrupt to the guest.

You can find the script at

'https://gitlab.com/maximlevitsky/vm_scripts/blob/master/tests/stest0.sh'

** Interrupts test **

For this test, the client was the kernel nvme driver, and fio running on top of it,
also with queue depth 1.
The test is at

'https://gitlab.com/maximlevitsky/vm_scripts/blob/master/tests/test0.sh'

The tests were done on Intel(R) Xeon(R) Gold 6128 CPU @ 3.40GHz,
with Optane SSD 900P NVME drive.

The system is dual socket, but the system was booted with configuration
that allowed to fully use only NUMA node 0, where the device is attached.

** The results for non interrupt test **

host:
BW :574.93 MiB/s (stdev:0.73 Mib/s)
IOPS :147,182 (stdev:186 IOPS/s)
SLAT :0.113 us (stdev:0.055 us)
CLAT :6.402 us (stdev:1.146 us)
LAT :6.516 us (stdev:1.148 us)

mdev/direct:

BW :535.99 MiB/s (stdev:2.62 Mib/s)
IOPS :137,214 (stdev:670 IOPS/s)
SLAT :0.128 us (stdev:3.074 us)
CLAT :6.909 us (stdev:4.384 us)
LAT :7.038 us (stdev:6.892 us)

commands translated : avg cycles: 668.032 avg time(usec): 0.196 total: 8239732
commands completed : avg cycles: 411.791 avg time(usec): 0.121 total: 8239732

mdev/block generic:

BW :512.99 MiB/s (stdev:2.5 Mib/s)
IOPS :131,324 (stdev:641 IOPS/s)
SLAT :0.13 us (stdev:3.143 us)
CLAT :7.237 us (stdev:4.516 us)
LAT :7.367 us (stdev:7.069 us)

commands translated : avg cycles: 1509.207 avg time(usec): 0.444 total: 7879519
commands completed : avg cycles: 1005.299 avg time(usec): 0.296 total: 7879519

*Here you clearly see the overhead added by the block layer*

spdk:
BW :535.77 MiB/s (stdev:0.86 Mib/s)
IOPS :137,157 (stdev:220 IOPS/s)
SLAT :0.135 us (stdev:0.073 us)
CLAT :6.905 us (stdev:1.166 us)
LAT :7.04 us (stdev:1.168 us)

qemu userspace nvme driver:
BW :151.56 MiB/s (stdev:0.38 Mib/s)
IOPS :38,799 (stdev:97 IOPS/s)
SLAT :4.655 us (stdev:0.714 us)
CLAT :20.856 us (stdev:1.993 us)
LAT :25.512 us (stdev:2.086 us)

** The results from interrupt test **

host:
BW :428.37 MiB/s (stdev:0.44 Mib/s)
IOPS :109,662 (stdev:112 IOPS/s)
SLAT :0.913 us (stdev:0.077 us)
CLAT :7.894 us (stdev:1.152 us)
LAT :8.844 us (stdev:1.155 us)

mdev/direct:
BW :401.33 MiB/s (stdev:1.99 Mib/s)
IOPS :102,739 (stdev:509 IOPS/s)
SLAT :0.916 us (stdev:3.588 us)
CLAT :8.544 us (stdev:1.21 us)
LAT :9.494 us (stdev:10.569 us)

commands translated : avg cycles: 639.993 avg time(usec): 0.188 total: 6164505
commands completed : avg cycles: 398.824 avg time(usec): 0.117 total: 6164505
interrupts sent : avg cycles: 612.795 avg time(usec): 0.18 total: 6164505

mdev/generic:
BW :384.35 MiB/s (stdev:1.89 Mib/s)
IOPS :98,394 (stdev:483 IOPS/s)
SLAT :0.986 us (stdev:3.668 us)
CLAT :8.86 us (stdev:8.584 us)
LAT :9.897 us (stdev:9.336 us)

commands translated : avg cycles: 1537.659 avg time(usec): 0.452 total: 5903703
commands completed : avg cycles: 976.604 avg time(usec): 0.287 total: 5903703
interrupts sent : avg cycles: 596.916 avg time(usec): 0.176 total: 5903703

spdk:
BW :395.11 MiB/s (stdev:0.54 Mib/s)
IOPS :101,149 (stdev:137 IOPS/s)
SLAT :0.857 us (stdev:0.123 us)
CLAT :8.755 us (stdev:1.224 us)
LAT :9.644 us (stdev:1.229 us)

aio_kernel/virtio_blk (other combinations showed similiar, a bit worse latency):

BW :176.27 MiB/s (stdev:3.14 Mib/s)
IOPS :45,125 (stdev:804 IOPS/s)
SLAT :1.584 us (stdev:0.375 us)
CLAT :20.291 us (stdev:2.031 us)
LAT :21.91 us (stdev:2.057 us)

qemu userspace driver:

BW :119.51 MiB/s (stdev:0.8 Mib/s)
IOPS :30,595 (stdev:203 IOPS/s)
SLAT :4.976 us (stdev:0.71 us)
CLAT :27.304 us (stdev:2.668 us)
LAT :32.336 us (stdev:2.736 us)

*** FAQ ***

* Why to make this in the kernel? Why this is better that SPDK

-> Reuse the existing nvme kernel driver in the host. No new drivers in the guest.

-> Share the NVMe device between host and guest.
Even in fully virtualized configurations,
some partitions of nvme device could be used by guests as block devices
while others passed through with nvme-mdev to achieve balance between
all features of full IO stack emulation and performance.

-> This is a framework that later can be used to support NVMe devices
with more of the IO virtualization built-in
(IOMMU with PASID support coupled with device that supports it)

* Why to attach directly to nvme-pci driver and not use block layer IO
-> The direct attachment allows for better performance (2x),
but it is possible to use block layer IO, especially for fabrics drivers, and/or
non nvme block devices.

*** Testing ***

The device was tested with mostly stock QEMU 4 on the host,
with host was using 5.1-rc6 kernel with nvme-mdev added and the following hardware:
* QEMU nvme virtual device (with nested guest)
* Intel DC P3700 on Xeon E5-2620 v2 server
* Intel Corporation Optane SSD 900P Series
* Samsung SM981 (in a Thunderbolt enclosure, with my laptop)
* Lenovo NVME device found in my laptop

The guest was tested with kernel 4.16, 4.18, 4.20 and
the same custom complied kernel 5.0
Windows 10 guest was tested too with both Microsoft's inbox driver and
open source community NVME driver
(https://lists.openfabrics.org/pipermail/nvmewin/2016-December/001420.html)

Testing was mostly done on x86_64, but 32 bit host/guest combination
was lightly tested too.

In addition to that, the virtual device was tested with nested guest,
by passing the virtual device to it,
using pci passthrough, qemu userspace nvme driver, and spdk

Maxim Levitsky (10):
vfio/mdev: add notifier for map events
vfio/mdev: add .request callback
nvme/core: add some more values from the spec
nvme/core: add NVME_CTRL_SUSPENDED controller state
nvme/pci: use the NVME_CTRL_SUSPENDED state
nvme/core: add mdev interfaces
nvme/core: add nvme-mdev core driver
nvme/pci: implement the mdev external queue allocation interface
nvme/mdev - Add inline performance measurments
nvme/mdev - generic block IO POC

MAINTAINERS | 5 +
drivers/nvme/Kconfig | 1 +
drivers/nvme/Makefile | 1 +
drivers/nvme/host/core.c | 144 +++++-
drivers/nvme/host/nvme.h | 55 +-
drivers/nvme/host/pci.c | 381 +++++++++++++-
drivers/nvme/mdev/Kconfig | 24 +
drivers/nvme/mdev/Makefile | 5 +
drivers/nvme/mdev/adm.c | 873 ++++++++++++++++++++++++++++++++
drivers/nvme/mdev/events.c | 142 ++++++
drivers/nvme/mdev/host.c | 741 +++++++++++++++++++++++++++
drivers/nvme/mdev/instance.c | 866 +++++++++++++++++++++++++++++++
drivers/nvme/mdev/io.c | 601 ++++++++++++++++++++++
drivers/nvme/mdev/irq.c | 270 ++++++++++
drivers/nvme/mdev/mdev.h | 56 ++
drivers/nvme/mdev/mmio.c | 588 +++++++++++++++++++++
drivers/nvme/mdev/pci.c | 247 +++++++++
drivers/nvme/mdev/priv.h | 774 ++++++++++++++++++++++++++++
drivers/nvme/mdev/udata.c | 390 ++++++++++++++
drivers/nvme/mdev/vcq.c | 209 ++++++++
drivers/nvme/mdev/vctrl.c | 518 +++++++++++++++++++
drivers/nvme/mdev/viommu.c | 322 ++++++++++++
drivers/nvme/mdev/vns.c | 356 +++++++++++++
drivers/nvme/mdev/vsq.c | 181 +++++++
drivers/vfio/mdev/vfio_mdev.c | 11 +
drivers/vfio/vfio_iommu_type1.c | 97 +++-
include/linux/mdev.h | 4 +
include/linux/nvme.h | 88 +++-
include/linux/vfio.h | 4 +
29 files changed, 7905 insertions(+), 49 deletions(-)
create mode 100644 drivers/nvme/mdev/Kconfig
create mode 100644 drivers/nvme/mdev/Makefile
create mode 100644 drivers/nvme/mdev/adm.c
create mode 100644 drivers/nvme/mdev/events.c
create mode 100644 drivers/nvme/mdev/host.c
create mode 100644 drivers/nvme/mdev/instance.c
create mode 100644 drivers/nvme/mdev/io.c
create mode 100644 drivers/nvme/mdev/irq.c
create mode 100644 drivers/nvme/mdev/mdev.h
create mode 100644 drivers/nvme/mdev/mmio.c
create mode 100644 drivers/nvme/mdev/pci.c
create mode 100644 drivers/nvme/mdev/priv.h
create mode 100644 drivers/nvme/mdev/udata.c
create mode 100644 drivers/nvme/mdev/vcq.c
create mode 100644 drivers/nvme/mdev/vctrl.c
create mode 100644 drivers/nvme/mdev/viommu.c
create mode 100644 drivers/nvme/mdev/vns.c
create mode 100644 drivers/nvme/mdev/vsq.c

--
2.17.2