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

[Nilay Shroff <nilay@linux.ibm.com>]

Hi Hannes and Sagi,

A gentle ping on this. Did you get a chance to look through this?

Please let me know if you still have any further comments.

Thanks,
--Nilay

On 11/12/24 10:07, Nilay Shroff wrote:
> 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(-)
>>