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

From: Wen Gu
Date: Fri Jan 12 2024 - 03:30:10 EST

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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.

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!

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

Next message: Ilpo Järvinen: "Re: [PATCH v2] platform/x86: silicom-platform: clean up a check"
Previous message: Krzysztof Kozlowski: "Re: Proposal for QCOM PCIe switch power and configuration driver"
In reply to: Jiri Pirko: "Re: [PATCH net-next 00/15] net/smc: implement loopback-ism used by SMC-D"
Next in thread: Jiri Pirko: "Re: [PATCH net-next 00/15] net/smc: implement loopback-ism used by SMC-D"
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