netdev - Re: [question] smc: how to enable SMC

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Date: Mon, 4 Dec 2023 11:22:27 +0800
From: shaozhengchao <shaozhengchao@...wei.com>
To: Wen Gu <guwen@...ux.alibaba.com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, yuehaibing
	<yuehaibing@...wei.com>, "Libin (Huawei)" <huawei.libin@...wei.com>, Dust Li
	<dust.li@...ux.alibaba.com>, tonylu_linux <tonylu@...ux.alibaba.com>, "D.
 Wythe" <alibuda@...ux.alibaba.com>
Subject: Re: [question] smc: how to enable SMC_LO feature



On 2023/11/23 14:15, shaozhengchao wrote:
> 
> 
> On 2023/11/23 10:21, Wen Gu wrote:
>>
>>
>> On 2023/11/21 20:14, shaozhengchao wrote:
>>> Hi Wen Gu:
>>> Currently, I am interested in the SMC_LOOPBACK feature proposed
>>> by you. Therefore, I use your patchset[1] to test the SMC_LO feature on
>>> my x86_64 environment and kernel is based on linux-next, commit: 
>>> 5ba73bec5e7b.
>>> The test result shows that the smc_lo feature cannot be enabled. Here's
>>> my analysis:
>>>
>>> 1. Run the following command to perform the test, and then capture
>>> packets on the lo device.
>>> - serv:  smc_run taskset -c <cpu> sockperf sr --tcp
>>> - clnt:  smc_run taskset -c <cpu> sockperf  tp --tcp --msg-size=64000 
>>> -i 127.0.0.1 -t 30
>>>
>>> 2. Use Wireshark to open packets. It is found that the VCE port 
>>> replies with
>>> SMC-R-Deline packets.
>>> [cid:image001.png@...A1CB4.F1052C30]
>>>
>>> 3. Rx
>>> When smc_listen_work invokes smc_listen_v2_check, the VCE port returns
>>> a Decline packet because eid_cnt and flag.seid in the received packet 
>>> are both 0.
>>>
>>> 4. Tx
>>> In smc_clc_send_proposal,
>>> v2_ext->hdr.eid_cnt = smc_clc_eid_table.ueid_cnt;
>>> v2_ext->hdr.flag.seid = smc_clc_eid_table.seid_enabled;
>>>
>>> When smc_clc_init, ueid_cnt=0, and in the x86_64 environment, 
>>> seid_enabled is
>>> always equal to 0.
>>>
>>> So, I must call smc_clc_ueid_add function to increase ueid count?
>>> But I don't see where operations can be added, may I missed something?
>>>
>>
>> Hi Zhengchao Shao,
>>
>> Yes. When using SMC-D in non-s390 architecture (like x86 here), A common
>> UEID should be set. It can be set by following steps:
>>
>> - Install smc-tools[1].
>>
>> - Run # smcd ueid add <ueid> in loopback test environment.
>>
>>    EID works as an ID to indicate the max communication space of SMC. 
>> When SEID is
>>    unavailable, an UEID is required.
>>
> Hi Wen Gu:
>      Thank you for your reply. This is very useful for me. And I will
> be happy to learn from it.
> 
> Thanks
> 
> Zhengchao Shao
>> - Then run the test.
>>
>> Hope this works for you :)
>>
>> [1] https://github.com/ibm-s390-linux/smc-tools
>>
>> Regards,
>> Wen Gu
>>
>>> Could you give me some advice? Thanks very much.
>>>
>>> Zhengchao Shao
>>>
>>>
>>> [1]link: 
>>> https://patchwork.kernel.org/project/netdevbpf/cover/1695568613-125057-1-git-send-email-guwen@linux.alibaba.com/
>>>
>>
> 
> 
Hi Wen Gu:
	I have test as following, but the performance is really
degraded. Now I have no idea.
1. add ueid
run: smcd ueid add 16
kernel message:
[ 5252.009133] NET: Registered PF_SMC protocol family
[ 5252.009233] smc: adding smcd device smc_lo with pnetid
2. start server
smc_run taskset -c 1 sockperf sr --tcp
3. start client
smc_run taskset -c 3 sockperf tp  --tcp --msg-size=64000 -i 127.0.0.1 -t 30

The test results are as follows:
			  TCP                  SMC-lo
Bandwidth(MBps)         1890.56               1300.41(-31.22%)

I didn't find a better direction when I initially positioned it. No
error is recorded in the kernel log, and the smcd statistics are normal.
[root@...alhost smc-tools]# smcd stats
SMC-D Connections Summary
   Total connections handled             2
   SMC connections                       2
   Handshake errors                      0
   Avg requests per SMC conn       1277462.0
   TCP fallback                          0

RX Stats
   Data transmitted (Bytes)    40907328000 (40.91G)
   Total requests                  1277190
   Buffer full                          45 (0.00%)
             8KB    16KB    32KB    64KB   128KB   256KB   512KB  >512KB
   Bufs        0       0       0       2       0       0       0       0
   Reqs   638.0K       0       0  639.2K       0       0       0       0

TX Stats
   Data transmitted (Bytes)    40907328000 (40.91G)
   Total requests                  1277734
   Buffer full                      638239 (49.95%)
   Buffer full (remote)                  0 (0.00%)
   Buffer too small                      0 (0.00%)
   Buffer too small (remote)             0 (0.00%)
             8KB    16KB    32KB    64KB   128KB   256KB   512KB  >512KB
   Bufs        0       0       0       0       0       0       0       0
   Reqs        0       0       0  1.278M       0       0       0       0

Extras
   Special socket calls                  1

I captured the perf information and found that the percentage of
rep_movs_alternative and _raw_spin_unlock_irqrestore functions was high
during tx and rx.
36.12%  [kernel]         [k]rep_movs_alternative
14.23%  [kernel]         [k]_raw_spin_unlock_irqrestore

I've attached the flame map. Could you help analyze it? What I missed?
Thanks.

Zhengchao Shao
Download attachment "smc.svg" of type "image/svg+xml" (61577 bytes)