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

From: Jiri Pirko
Date: Fri Jan 12 2024 - 04:10:35 EST

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Fri, Jan 12, 2024 at 09:29:35AM CET, guwen@xxxxxxxxxxxxxxxxx wrote:
>
>
>On 2024/1/11 22:50, Jiri Pirko wrote:
>> Thu, Jan 11, 2024 at 01:00:21PM CET, guwen@xxxxxxxxxxxxxxxxx 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@xxxxxxxxxxxxxxxxx/)
>
>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@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 (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
>> >
>> >

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