Re: [PATCHv5 RFC 0/3] Add visibility for native NVMe multipath using sysfs

Nilay Shroff
2024-11-12T04:38:03Z

Hi Hannes and Sagi,

A gentle ping... I have addressed your suggestions in this patch series.
Does this now look okay to you or do you have any further suggestions/comments?

Thanks,
--Nilay

On 10/30/24 16:11, Nilay Shroff wrote:
> Hi,
>
> This RFC propose adding new sysfs attributes for adding visibility of
> nvme native multipath I/O.
>
> The changes are divided into three patches.
> The first patch adds visibility for round-robin io-policy.
> The second patch adds visibility for numa io-policy.
> The third patch adds the visibility for queue-depth io-policy.
>
> As we know, NVMe native multipath supports three different io policies
> (numa, round-robin and queue-depth) for selecting I/O path, however, we
> don't have any visibility about which path is being selected by multipath
> code for forwarding I/O. This RFC helps add that visibility by adding new
> sysfs attribute files named "numa_nodes" and "queue_depth" under each
> namespace block device path /sys/block/nvmeXcYnZ/. We also create a
> "multipath" sysfs directory under head disk node and then from this
> directory add a link to each namespace path device this head disk node
> points to.
>
> Please find below output generated with this proposed RFC patch applied on
> a system with two multi-controller PCIe NVMe disks attached to it. This
> system is also an NVMf-TCP host which is connected to an NVMf-TCP target
> over two NIC cards. This system has four numa nodes online when the below
> output was captured:
>
> # cat /sys/devices/system/node/online
> 0-3
>
> # lscpu
> <snip>
> NUMA:
> NUMA node(s): 4
> NUMA node0 CPU(s):
> NUMA node1 CPU(s): 0-7
> NUMA node2 CPU(s): 8-31
> NUMA node3 CPU(s): 32-63
> <snip>
>
> Please note that numa node 0 though online, doesn't have any CPU
> currently assigned to it.
>
> # nvme list -v
> Subsystem Subsystem-NQN Controllers
> ---------------- ------------------------------------------------------------------------------------------------ ----------------
> nvme-subsys1 nqn.1994-11.com.samsung:nvme:PM1735a:2.5-inch:S6RTNE0R900057 nvme0, nvme1
> nvme-subsys3 nqn.2019-10.com.kioxia:KCM7DRUG1T92:3D60A04906N1 nvme2, nvme3
> nvme-subsys4 nvmet_subsystem nvme4, nvme5
>
> Device Cntlid SN MN FR TxPort Address Slot Subsystem Namespaces
> ---------------- ------ -------------------- ---------------------------------------- -------- ------ -------------- ------ ------------ ----------------
> nvme0 66 S6RTNE0R900057 3.2TB NVMe Gen4 U.2 SSD III REV.SN66 pcie 052e:78:00.0 U50EE.001.WZS000E-P3-C14-R1 nvme-subsys1 nvme1n1
> nvme1 65 S6RTNE0R900057 3.2TB NVMe Gen4 U.2 SSD III REV.SN66 pcie 058e:78:00.0 U50EE.001.WZS000E-P3-C14-R2 nvme-subsys1 nvme1n1
> nvme2 2 3D60A04906N1 1.6TB NVMe Gen4 U.2 SSD IV REV.CAS2 pcie 0524:28:00.0 U50EE.001.WZS000E-P3-C4-R1 nvme-subsys3 nvme3n1
> nvme3 1 3D60A04906N1 1.6TB NVMe Gen4 U.2 SSD IV REV.CAS2 pcie 0584:28:00.0 U50EE.001.WZS000E-P3-C4-R2 nvme-subsys3 nvme3n1
> nvme4 1 a224673364d1dcb6fab9 Linux 6.9.0-rc tcp traddr=20.0.0.200,trsvcid=4420,src_addr=20.0.0.100 nvme-subsys4 nvme4n1
> nvme5 2 a224673364d1dcb6fab9 Linux 6.9.0-rc tcp traddr=10.0.0.200,trsvcid=4420,src_addr=10.0.0.100 nvme-subsys4 nvme4n1
>
> Device Generic NSID Usage Format Controllers
> ----------------- ----------------- ---------- -------------------------- ---------------- ----------------
> /dev/nvme1n1 /dev/ng1n1 0x1 5.75 GB / 5.75 GB 4 KiB + 0 B nvme0, nvme1
> /dev/nvme3n1 /dev/ng3n1 0x2 0.00 B / 5.75 GB 4 KiB + 0 B nvme2, nvme3
> /dev/nvme4n1 /dev/ng4n1 0x1 5.75 GB / 5.75 GB 4 KiB + 0 B nvme4, nvme5
>
>
> # nvme show-topology
> nvme-subsys1 - NQN=nqn.1994-11.com.samsung:nvme:PM1735a:2.5-inch:S6RTNE0R900057
> hostnqn=nqn.2014-08.org.nvmexpress:uuid:41528538-e8ad-4eaf-84a7-9c552917d988
> iopolicy=numa
> \
> +- ns 1
> \
> +- nvme0 pcie 052e:78:00.0 live optimized
> +- nvme1 pcie 058e:78:00.0 live optimized
>
> nvme-subsys3 - NQN=nqn.2019-10.com.kioxia:KCM7DRUG1T92:3D60A04906N1
> hostnqn=nqn.2014-08.org.nvmexpress:uuid:41528538-e8ad-4eaf-84a7-9c552917d988
> iopolicy=round-robin
> \
> +- ns 2
> \
> +- nvme2 pcie 0524:28:00.0 live optimized
> +- nvme3 pcie 0584:28:00.0 live optimized
>
> nvme-subsys4 - NQN=nvmet_subsystem
> hostnqn=nqn.2014-08.org.nvmexpress:uuid:41528538-e8ad-4eaf-84a7-9c552917d988
> iopolicy=queue-depth
> \
> +- ns 1
> \
> +- nvme4 tcp traddr=20.0.0.200,trsvcid=4420,src_addr=20.0.0.100 live optimized
> +- nvme5 tcp traddr=10.0.0.200,trsvcid=4420,src_addr=10.0.0.100 live optimized
>
> As we could see above, we've three shared namespaces created. In terms of
> iopolicy, we have "numa" configured for nvme-subsys1, "round-robin"
> configured for nvme-subsys3 and "queue-depth" configured for nvme-subsys4.
>
> Now, under each namespace "head disk node", we create a sysfs group
> attribute named "multipath". The "multipath" group then points to the
> each path this head disk node points to:
>
> # tree /sys/block/nvme1n1/multipath/
> /sys/block/nvme1n1/multipath/
> ├── nvme1c0n1 -> ../../../../../pci052e:78/052e:78:00.0/nvme/nvme0/nvme1c0n1
> └── nvme1c1n1 -> ../../../../../pci058e:78/058e:78:00.0/nvme/nvme1/nvme1c1n1
>
> # tree /sys/block/nvme3n1/multipath/
> /sys/block/nvme3n1/multipath/
> ├── nvme3c2n1 -> ../../../../../pci0524:28/0524:28:00.0/nvme/nvme2/nvme3c2n1
> └── nvme3c3n1 -> ../../../../../pci0584:28/0584:28:00.0/nvme/nvme3/nvme3c3n1
>
> # tree /sys/block/nvme4n1/multipath/
> /sys/block/nvme4n1/multipath/
> ├── nvme4c4n1 -> ../../../../nvme-fabrics/ctl/nvme4/nvme4c4n1
> └── nvme4c5n1 -> ../../../../nvme-fabrics/ctl/nvme5/nvme4c5n1
>
> One can easily infer from the above output that for the "round-robin"
> I/O policy, configured under nvme-subsys3, the I/O workload targeted at
> nvme3n1 would toggle across nvme3c2n1 and nvme3c3n1 assuming the ana state
> of each path is optimized (as can be seen in the output of show-topology).
>
> For numa I/O policy, configured under nvme-subsys1, the "numa_nodes"
> attribute file shows the numa nodes being preferred by the respective
> namespace path. The numa nodes value is comma delimited list of nodes or
> A-B range of nodes.
>
> # cat /sys/block/nvme1n1/multipath/nvme1c0n1/numa_nodes
> 0-1
>
> # cat /sys/block/nvme1n1/multipath/nvme1c1n1/numa_nodes
> 2-3
>
> From the above output, one can easily infer that I/O workload targeted at
> nvme1n1 and running on numa nodes 0 and 1 would use path nvme1c0n1.
> Similarly, I/O workload running on numa nodes 2 and 3 would use path
> nvme1c1n1.
>
> For queue-depth I/O policy, configured under nvme-subsys4, the "queue_depth"
> attribute file shows the number of active/in-flight I/O requests currently
> queued for each path.
>
> # cat /sys/block/nvme4n1/multipath/nvme4c4n1/queue_depth
> 518
>
> # cat /sys/block/nvme4n1/multipath/nvme4c5n1/queue_depth
> 504
>
> From the above output, one can easily infer that I/O workload targeted at
> nvme4n1 uses two paths nvme4c4n1 and nvme4c5n1 and the current queue depth
> of each path is 518 and 504 respectively.
>
> changes since v4:
> - Ensure that we create sysfs link from head gendisk node to each path
> device irrespective of the ANA state of the path (Hannes Reinecke)
> - Split the patch into three patch series and add commentary in the
> code so that it's easy to read and understand the core logic (Sagi
> Grimberg)
> - Don't show any output if user reads "numa_nodes" file and configured
> iopolicy is anything but numa; similarly don't emit any output if user
> reads "queue_depth" file and configured iopolicy is anything but
> queue-depth (Sagi Grimberg)
>
> Changes since v3:
> - Protect the namespace dereference code with srcu read lock (Daniel Wagner)
>
> Changes since v2:
> - Use one value per one sysfs attribute (Keith Busch)
>
> Changes since v1:
> - Use sysfs to export multipath I/O information instead of debugfs
>
>
> Nilay Shroff (3):
> nvme-multipah: Add visibility for round-robin io-policy
> nvme-multipath: Add visibility for numa io-policy
> nvme-multipath: Add visibility for queue-depth io-policy
>
> drivers/nvme/host/core.c | 3 +
> drivers/nvme/host/multipath.c | 120 ++++++++++++++++++++++++++++++++++
> drivers/nvme/host/nvme.h | 20 ++++--
> drivers/nvme/host/sysfs.c | 20 ++++++
> 4 files changed, 159 insertions(+), 4 deletions(-)
>