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

From: Wenjia Zhang
Date: Fri Feb 16 2024 - 09:10:23 EST

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On 11.01.24 13:00, 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.

# 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 virtual 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-#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,
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

Hi Wen,

Thank you for the patience again!

You can find the comments under the corresponding patches respectively.
About the file hierarchy in sysfs and the names, we still have some thoughts. We need to investigate a bit more time on it.

Thanks,
Gerd & Wenjia

Next message: Saurabh Sengar: "[PATCH] Drivers: hv: Kconfig: select CPUMASK_OFFSTACK for Hyper-V"
Previous message: Geert Uytterhoeven: "Re: [PATCH 09/17] clk: renesas: r9a07g044: Add initial support for power domains"
Next in thread: Wen Gu: "Re: [PATCH net-next 00/15] net/smc: implement loopback-ism used by SMC-D"
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