Re: [PATCH net-next 00/15] net/smc: implement loopback-ism used by SMC-D

[Jiri Pirko <jiri@resnulli.us>]

Fri, Jan 12, 2024 at 09:29:35AM CET, guwen@linux.alibaba.com wrote:
>
>
>On 2024/1/11 22:50, Jiri Pirko wrote:
>> Thu, Jan 11, 2024 at 01:00:21PM CET, guwen@linux.alibaba.com 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.
>> > 
>> > # 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
>> 
>> Care to provide more details about what ISM and intra-CPC is and what it
>> it good for?
>> 
>
>Hi Jiri,
>
>Sure,
>
>ISM (IBM System Z Internal Shared Memory) is a technology that provides the
>internal communications capability required for SMC-D. It is a virtual PCI
>network adapter that enables direct access to shared virtual memory providing
>a highly optimized network interconnect for IBM Z intra-CPC communications.
>(It can be found in https://www.ibm.com/docs/en/zos/3.1.0?topic=communications-shared-memory-reference-information
>and https://www.ibm.com/docs/en/zos/3.1.0?topic=dv2-ismv2)
>
>CPC (Central processor complex) is an IBM mainframe term to refer to the physical
>collection of hardware that includes main storage, one or more central processors,
>timers, and channels.
>(It can be found in https://www.ibm.com/docs/en/zos-basic-skills?topic=concepts-mainframe-hardware-terminology
>and https://www.ibm.com/docs/en/ztpf/2023?topic=support-central-processor-complex-cpc)
>
>SMC (Shared Memory Communications) is a network protocol that allows two SMC
>capable peers to communicate using memory that each peer allocates and manages
>for their partner’s use. It has two forms:
>
>- SMC over Remote Direct Memory Access (SMC-R)
>
>  It is an open protocol that was initially introduced in z/OS V2R1 on the IBM zEC12.
>  SMC-R is defined in an informational RFC entitled IBM’s Shared Memory Communications
>  over RDMA (https://tools.ietf.org/html/rfc7609).
>
>- SMC - Direct Memory Access (SMC-D)
>
>  It is a variation of SMC-R. SMC-D is closely related to SMC-R but is based on the
>  Internal Shared Memory (ISM) capabilities introduced with the IBM z13™ (z13) hardware
>  model.
>
>(SMC protocol can be found in https://www.ibm.com/support/pages/system/files/inline-files/IBM%20Shared%20Memory%20Communications%20Version%202.1_0.pdf)
>
>So with ISM function, SMC-D can be used to improves throughput, lowers latency and cost,
>and maintains existing functions of communications within CPC.
>
>> 
>> > on the non-s390 architecture through a software-implemented virtual ISM device,
>> > that is the loopback-ism device here, to accelerate inter-process or
>> 
>> I see no such device. Is it a netdevice?
>
>Currently, SMC-D depends on ISM and is only available on IBM Z systems. Now we try
>to make SMC-D available on other system architectures other than s390 and Z system.
>So 'virtual ISM' is proposed and acts as original firmware ISM on Z system.
>(The virtual ISM supports can be found in https://lore.kernel.org/netdev/20231219142616.80697-1-guwen@linux.alibaba.com/)
>
>The loopback-ism is the first virtual ISM. It does not rely on a specific architecture
>or hardware, and provides functions that ISM should have (like a dummy device). It is
>designed to be used by SMC-D when communication occurs within OS instance.
>
>It is not a typical network device, since it primarily provides exact functions
>defined by SMC-D device operations(struct smcd_ops), e.g. provides and manages the
>shared memory (term used is DMB in SMC, Direct Memory Buffer).
>
>It can't be found now since it is introduced by this patchset.
>
>> 
>> If it is "software-implemented", why is it part of smc driver and not
>> separate soft-device driver? If there is some smc specific code, I guess
>> there should be some level of separation. Can't this be implemented by
>> other devices too?
>> 
>
>loopback-ism is designed to specifically used by SMC-D (like s390 ISM), to
>serves as a easy-available ISM for community to test SMC-D and to accelerate
>intra-OS communication (see benchmark test). So the code is under net/smc.

Got it.


>
>> 
>> 
>> > inter-containers communication within the same OS instance.
>> > 
>> > # Design
>> > 
>> > This patch set includes 3 parts:
>> > 
>> > - Patch #1-#2: some prepare work for loopback-ism.
>> > - Patch #3-#9: implement loopback-ism device.
>> > - Patch #10-#15: memory copy optimization for loopback scenario.
>> > 
>> > The loopback-ism device is designed as a 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.
>> >       - /sys/devices/virtual/smc/loopback-ism/dmb_copy is set to default 0,
>> >         which means sndbuf and DMB are merged and no data copied between them.
>> >       - /sys/devices/virtual/smc/loopback-ism/dmb_type is set to default 0,
>> 
>> Exposing any configuration knobs and statistics over sysfs for
>> softdevices does not look correct at all :/ Could you please avoid
>> sysfs?
>> 
>
>In previous reviews and calls, we think loopback-ism needs to be more
>like a device and be visible under /sys/devices.
>
>Would you mind explaining why using sysfs for loopback-ism is not correct?
>since I saw some other configurations or statistics exists under /sys/devices,
>e.g. /sys/devices/virtual/net/lo. Thank you!

You have smc_netlink.c exposing clear netlink api for the subsystem.
Can't you extend it to contain the configuration knobs and expose stats
instead of sysfs?


>
>
>
>Thanks again,
>Wen Gu
>
>> 
>> >         which means DMB is physically contiguous buffer.
>> > 
>> > * Test object:
>> >       - TCP: run on TCP loopback.
>> >       - SMC lo: run on SMC loopback device.
>> > 
>> > 1. ipc-benchmark (see [3])
>> > 
>> > - ./<foo> -c 1000000 -s 100
>> > 
>> >                             TCP                  SMC-lo
>> > Message
>> > rate (msg/s)              80636                  149515(+85.42%)
>> > 
>> > 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)         4909.36                 8197.57(+66.98%)
>> > Latency(us)               6.098                   3.383(-44.52%)
>> > 
>> > 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           181685.74                246447.77(+35.65%)
>> > 
>> > 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)       85855.34                118553.64(+38.09%)
>> > SET(Requests/s)       86824.40                125944.58(+45.06%)
>> > 
>> > 
>> > Change log:
>> > 
>> > v1->RFC:
>> > - 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@linux.alibaba.com/
>> > - 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@linux.alibaba.com/
>> > [2] https://lore.kernel.org/netdev/20231219142616.80697-1-guwen@linux.alibaba.com/
>> > [3] https://github.com/goldsborough/ipc-bench
>> > [4] https://lore.kernel.org/all/3189e342-c38f-6076-b730-19a6efd732a5@linux.alibaba.com/
>> > [5] https://lore.kernel.org/all/238e63cd-e0e8-4fbf-852f-bc4d5bc35d5a@linux.alibaba.com/
>> > [6] https://lore.kernel.org/all/20240102184633.748113-1-urezki@gmail.com/
>> > 
>> > Wen Gu (15):
>> >   net/smc: improve SMC-D device dump for virtual ISM
>> >   net/smc: decouple specialized struct from SMC-D DMB registration
>> >   net/smc: introduce virtual ISM device loopback-ism
>> >   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: register loopback-ism into SMC-D device list
>> >   net/smc: introduce loopback-ism runtime switch
>> >   net/smc: introduce loopback-ism statistics attributes
>> >   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: introduce loopback-ism DMB type control
>> >   net/smc: introduce loopback-ism DMB data copy control
>> >   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          |  58 ++-
>> > net/smc/smc_cdc.h          |   1 +
>> > net/smc/smc_core.c         |  61 +++-
>> > net/smc/smc_core.h         |   1 +
>> > net/smc/smc_ism.c          |  71 +++-
>> > net/smc/smc_ism.h          |   5 +
>> > net/smc/smc_loopback.c     | 718 +++++++++++++++++++++++++++++++++++++
>> > net/smc/smc_loopback.h     |  88 +++++
>> > 13 files changed, 1026 insertions(+), 29 deletions(-)
>> > create mode 100644 net/smc/smc_loopback.c
>> > create mode 100644 net/smc/smc_loopback.h
>> > 
>> > -- 
>> > 2.32.0.3.g01195cf9f
>> > 
>> >