Re: [RFC PATCH net-next v4 00/11] net/smc: SMC intra-OS shortcut with loopback-ism

[Jan Karcher]

On 17/03/2024 11:05, Wen Gu wrote:
> This patch set acts as the second part of the new version of [1] (The first
> part can be referred from [2]), the updated things of this version are listed
> at the end.

Hi Wen Gu,

thanks for the v4. Please see my comments for the patches.
Testing looks good so far on s390.

Thanks
- Jan

> - Background
>
> SMC-D is now used in IBM z with ISM function to optimize network interconnect
> for intra-CPC communications. Inspired by this, we try to make SMC-D available
> on the non-s390 architecture through a software-implemented Emulated-ISM device,
> that is the loopback-ism device here, to accelerate inter-process or
> inter-containers communication within the same OS instance.
>
> - Design
>
> This patch set includes 3 parts:
>
>   - Patch #1: some prepare work for loopback-ism.
>   - Patch #2-#7: implement loopback-ism device. Noted that loopback-ism now
>     serves only SMC and no userspace interface exposed.
>   - Patch #8-#11: memory copy optimization for intra-OS scenario.
>
> The loopback-ism device is designed as an ISMv2 device and not be limited to
> a specific net namespace, ends of both inter-process connection (1/1' in diagram
> below) or inter-container connection (2/2' in diagram below) can find the same
> available loopback-ism and choose it during the CLC handshake.
>
>   Container 1 (ns1)                              Container 2 (ns2)
>   +-----------------------------------------+    +-------------------------+
>   | +-------+      +-------+      +-------+ |    |        +-------+        |
>   | | App A |      | App B |      | App C | |    |        | App D |<-+     |
>   | +-------+      +---^---+      +-------+ |    |        +-------+  |(2') |
>   |     |127.0.0.1 (1')|             |192.168.0.11       192.168.0.12|     |
>   |  (1)|   +--------+ | +--------+  |(2)   |    | +--------+   +--------+ |
>   |     `-->|   lo   |-` |  eth0  |<-`      |    | |   lo   |   |  eth0  | |
>   +---------+--|---^-+---+-----|--+---------+    +-+--------+---+-^------+-+
>                |   |           |                                  |
>   Kernel       |   |           |                                  |
>   +----+-------v---+-----------v----------------------------------+---+----+
>   |    |                            TCP                               |    |
>   |    |                                                              |    |
>   |    +--------------------------------------------------------------+    |
>   |                                                                        |
>   |                           +--------------+                             |
>   |                           | smc loopback |                             |
>   +---------------------------+--------------+-----------------------------+
>
> loopback-ism device creates DMBs (shared memory) for each connection peer.
> Since data transfer occurs within the same kernel, the sndbuf of each peer
> is only a descriptor and point to the same memory region as peer DMB, so that
> the data copy from sndbuf to peer DMB can be avoided in loopback-ism case.
>
>   Container 1 (ns1)                              Container 2 (ns2)
>   +-----------------------------------------+    +-------------------------+
>   | +-------+                               |    |        +-------+        |
>   | | App C |-----+                         |    |        | App D |        |
>   | +-------+     |                         |    |        +-^-----+        |
>   |               |                         |    |          |              |
>   |           (2) |                         |    |     (2') |              |
>   |               |                         |    |          |              |
>   +---------------|-------------------------+    +----------|--------------+
>                   |                                         |
>   Kernel          |                                         |
>   +---------------|-----------------------------------------|--------------+
>   | +--------+ +--v-----+                           +--------+ +--------+  |
>   | |dmb_desc| |snd_desc|                           |dmb_desc| |snd_desc|  |
>   | +-----|--+ +--|-----+                           +-----|--+ +--------+  |
>   | +-----|--+    |                                 +-----|--+             |
>   | | DMB C  |    +---------------------------------| DMB D  |             |
>   | +--------+                                      +--------+             |
>   |                                                                        |
>   |                           +--------------+                             |
>   |                           | smc loopback |                             |
>   +---------------------------+--------------+-----------------------------+
>
> - Benchmark Test
>
>   * Test environments:
>        - VM with Intel Xeon Platinum 8 core 2.50GHz, 16 GiB mem.
>        - SMC sndbuf/DMB size 1MB.
>
>   * Test object:
>        - TCP: run on TCP loopback.
>        - SMC lo: run on SMC loopback-ism.
>
> 1. ipc-benchmark (see [3])
>
>   - ./<foo> -c 1000000 -s 100
>
>                              TCP                  SMC-lo
> Message
> rate (msg/s)              81433                  143938(+76.75%)
>
> 2. sockperf
>
>   - serv: <smc_run> taskset -c <cpu> sockperf sr --tcp
>   - clnt: <smc_run> taskset -c <cpu> sockperf { tp | pp } --tcp --msg-size={ 64000 for tp | 14 for pp } -i 127.0.0.1 -t 30
>
>                              TCP                  SMC-lo
> Bandwidth(MBps)         4903.07                 7978.69(+62.73%)
> Latency(us)               6.095                   3.539(-41.94%)
>
> 3. nginx/wrk
>
>   - serv: <smc_run> nginx
>   - clnt: <smc_run> wrk -t 8 -c 1000 -d 30 http://127.0.0.1:80
>
>                             TCP                   SMC-lo
> Requests/s           161665.67                244272.41(+51.10%)
>
> 4. redis-benchmark
>
>   - serv: <smc_run> redis-server
>   - clnt: <smc_run> redis-benchmark -h 127.0.0.1 -q -t set,get -n 400000 -c 200 -d 1024
>
>                             TCP                   SMC-lo
> GET(Requests/s)       88790.23                117474.30(+32.31%)
> SET(Requests/s)       87508.20                118623.96(+35.57%)
>
>
> Change log:
>
> RFC v4->v3:
> - The merge window of v6.9 is open, so post this series as an RFC.
> - Patch #6: since some information fed back by smc_nl_handle_smcd_dev() dose
>    not apply to Emulated-ISM (including loopback-ism here), loopback-ism is
>    not exposed through smc netlink for the time being. we may refactor this
>    part when smc netlink interface is updated.
>
> v3->v2:
> Link: https://lore.kernel.org/netdev/20240312142743.41406-1-guwen@xxxxxxxxxxxxxxxxx/
> - Patch #11: use tasklet_schedule(&conn->rx_tsklet) instead of smcd_cdc_rx_handler()
>    to avoid possible recursive locking of conn->send_lock and use {read|write}_lock_bh()
>    to acquire dmb_ht_lock.
>
> v2->v1:
> Link: https://lore.kernel.org/netdev/20240307095536.29648-1-guwen@xxxxxxxxxxxxxxxxx/
> - All the patches: changed the term virtual-ISM to Emulated-ISM as defined by SMCv2.1.
> - Patch #3: optimized the description of SMC_LO config. Avoid exposing loopback-ism
>    to sysfs and remove all the knobs until future definition clear.
> - Patch #3: try to make lockdep happy by using read_lock_bh() in smc_lo_move_data().
> - Patch #6: defaultly use physical contiguous DMB buffers.
> - Patch #11: defaultly enable DMB no-copy for loopback-ism and free the DMB in
>    unregister_dmb or detach_dmb when dmb_node->refcnt reaches 0, instead of using
>    wait_event to keep waiting in unregister_dmb.
>
> v1->RFC:
> Link: https://lore.kernel.org/netdev/20240111120036.109903-1-guwen@xxxxxxxxxxxxxxxxx/
> - Patch #9: merge rx_bytes and tx_bytes as xfer_bytes statistics:
>    /sys/devices/virtual/smc/loopback-ism/xfer_bytes
> - Patch #10: add support_dmb_nocopy operation to check if SMC-D device supports
>    merging sndbuf with peer DMB.
> - Patch #13 & #14: introduce loopback-ism device control of DMB memory type and
>    control of whether to merge sndbuf and DMB. They can be respectively set by:
>    /sys/devices/virtual/smc/loopback-ism/dmb_type
>    /sys/devices/virtual/smc/loopback-ism/dmb_copy
>    The motivation for these two control is that a performance bottleneck was
>    found when using vzalloced DMB and sndbuf is merged with DMB, and there are
>    many CPUs and CONFIG_HARDENED_USERCOPY is set [4]. The bottleneck is caused
>    by the lock contention in vmap_area_lock [5] which is involved in memcpy_from_msg()
>    or memcpy_to_msg(). Currently, Uladzislau Rezki is working on mitigating the
>    vmap lock contention [6]. It has significant effects, but using virtual memory
>    still has additional overhead compared to using physical memory.
>    So this new version provides controls of dmb_type and dmb_copy to suit
>    different scenarios.
> - Some minor changes and comments improvements.
>
> RFC->old version([1]):
> Link: https://lore.kernel.org/netdev/1702214654-32069-1-git-send-email-guwen@xxxxxxxxxxxxxxxxx/
> - Patch #1: improve the loopback-ism dump, it shows as follows now:
>    # smcd d
>    FID  Type  PCI-ID        PCHID  InUse  #LGs  PNET-ID
>    0000 0     loopback-ism  ffff   No        0
> - Patch #3: introduce the smc_ism_set_v2_capable() helper and set
>    smc_ism_v2_capable when ISMv2 or virtual ISM is registered,
>    regardless of whether there is already a device in smcd device list.
> - Patch #3: loopback-ism will be added into /sys/devices/virtual/smc/loopback-ism/.
> - Patch #8: introduce the runtime switch /sys/devices/virtual/smc/loopback-ism/active
>    to activate or deactivate the loopback-ism.
> - Patch #9: introduce the statistics of loopback-ism by
>    /sys/devices/virtual/smc/loopback-ism/{{tx|rx}_tytes|dmbs_cnt}.
> - Some minor changes and comments improvements.
>
> [1] https://lore.kernel.org/netdev/1695568613-125057-1-git-send-email-guwen@xxxxxxxxxxxxxxxxx/
> [2] https://lore.kernel.org/netdev/20231219142616.80697-1-guwen@xxxxxxxxxxxxxxxxx/
> [3] https://github.com/goldsborough/ipc-bench
> [4] https://lore.kernel.org/all/3189e342-c38f-6076-b730-19a6efd732a5@xxxxxxxxxxxxxxxxx/
> [5] https://lore.kernel.org/all/238e63cd-e0e8-4fbf-852f-bc4d5bc35d5a@xxxxxxxxxxxxxxxxx/
> [6] https://lore.kernel.org/all/20240102184633.748113-1-urezki@xxxxxxxxx/
>
> Wen Gu (11):
>    net/smc: decouple ism_client from SMC-D DMB registration
>    net/smc: introduce loopback-ism for SMC intra-OS shortcut
>    net/smc: implement ID-related operations of loopback-ism
>    net/smc: implement some unsupported operations of loopback-ism
>    net/smc: implement DMB-related operations of loopback-ism
>    net/smc: ignore loopback-ism when dumping SMC-D devices
>    net/smc: register loopback-ism into SMC-D device list
>    net/smc: add operations to merge sndbuf with peer DMB
>    net/smc: attach or detach ghost sndbuf to peer DMB
>    net/smc: adapt cursor update when sndbuf and peer DMB are merged
>    net/smc: implement DMB-merged operations of loopback-ism
>
>   drivers/s390/net/ism_drv.c |   2 +-
>   include/net/smc.h          |   7 +-
>   net/smc/Kconfig            |  13 ++
>   net/smc/Makefile           |   2 +-
>   net/smc/af_smc.c           |  28 ++-
>   net/smc/smc_cdc.c          |  52 ++++-
>   net/smc/smc_core.c         |  61 ++++-
>   net/smc/smc_core.h         |   1 +
>   net/smc/smc_ism.c          |  60 ++++-
>   net/smc/smc_ism.h          |  10 +
>   net/smc/smc_loopback.c     | 462 +++++++++++++++++++++++++++++++++++++
>   net/smc/smc_loopback.h     |  52 +++++
>   12 files changed, 724 insertions(+), 26 deletions(-)
>   create mode 100644 net/smc/smc_loopback.c
>   create mode 100644 net/smc/smc_loopback.h