Date: Wed, 27 Dec 2023 09:12:23 +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 2023/12/26 19:52, Wen Gu wrote:
> 
> 
> On 2023/12/14 11:17, shaozhengchao wrote:
>>
>>
>> On 2023/12/13 20:59, Wen Gu wrote:
>>> On 2023/12/13 17:00, shaozhengchao wrote:
>>>>
>>>>
>>>> On 2023/12/5 14:45, shaozhengchao wrote:
>>>>>
>>>>>
>>>>> On 2023/12/4 12:06, shaozhengchao wrote:
>>>>>>
>>>>>>
>>>>>> On 2023/12/4 11:52, Wen Gu wrote:
>>>>>>>
>>>>>>> On 2023/12/4 11:22, shaozhengchao wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> 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.
>>>>>>>
>>>>>>> Hi Zhengchao Shao,
>>>>>>>
>>>>>>> Since sndbuf and RMB in SMC are pre-alloced ringbuf and won't 
>>>>>>> grow dynamically
>>>>>>> like TCP, it is necessary to appropriately increase the default 
>>>>>>> value of smc
>>>>>>> sk_sndbuf and sk_rcvbuf before testing throughput.
>>>>>>>
>>>>>>> Set this and try again:
>>>>>>>
>>>>>>> # sysctl -w net.smc.wmem=1048576
>>>>>>> # sysctl -w net.smc.rmem=1048576
>>>>>>>
>>>>>>> (The initial value of wmem and rmem are 64K)
>>>>>>>
>>>>>>> Regards,
>>>>>>> Wen Gu
>>>>>>>
>>>>>>>>
>>>>>>>> Zhengchao Shao
>>>>>> Hi Wen Gu:
>>>>>>      It solves the issue. Thank you very much.
>>>>>>
>>>>>> Zhengchao Shao
>>>>>>
>>>>> Hi Wen Gu:
>>>>>    I've tested all the performance test items in the patchset. The
>>>>> performance improvement is to be expected, except for nignx.
>>>>> My VM is configured with 48 cores and 32 GB memory. Therefore, run
>>>>> the following command:
>>>>> <smc_run> nignx
>>>>> <smc_run>./wrk -t 96 -c 1000 -d 30 http://127.0.0.1:80
>>>>>
>>>>> The test results are as follows:
>>>>>                          TCP                         SMC_lo
>>>>> Requests/s           309425.42               135547.25(-56.19%)
>>>>> The performance decreases by 56.19%.
>>>>>
>>>>> I capture packets and find that wrk can perform HTTP GET after each
>>>>> connect when smc_loopback is disabled.
>>>>> However, when smc_loopback is enabled, there is no HTTP GET behavior.
>>>>> I wonder if there is some compatibility problem with the SMC 
>>>>> protocol when encapsulate packet? Could you give me some advice?
>>>>> In the attachment, I captured some of the packets.
>>>>> nosmc_nginx.pcap is for SMC disabled and smc_nginx.pcap is for SMC
>>>>> enabled.
>>>>> Thank you very much.
>>>>>
>>>>> Zhengchao Shao
>>>>>
>>>>>
>>>>>
>>>> Hi Wen Gu:
>>>>      When the VM is configured with 8 cores and 16 GB memory, run
>>>> the following command:
>>>> <smc_run> nignx
>>>> <smc_run>./wrk -t 8 -c 1000 -d 30 http://127.0.0.1:80
>>>> the test data is as follows:
>>>>           TCP          SMC_lo
>>>> Requests/s  66056.66    94526.66(43.10%)
>>>>
>>>> But When the VM is configured with 48 cores and 32 GB memory, run
>>>> the following command:
>>>> <smc_run> nignx
>>>> <smc_run>./wrk -t 96 -c 1000 -d 30 http://127.0.0.1:80
>>>> the test data is as follows:
>>>>           TCP          SMC_lo
>>>> Requests/s  309425.42     135547.25(-56.19%)
>>>>
>>>> It seems that in the scenario with a large number of CPU cores,
>>>> performance is not optimized, but performance deteriorates. What I
>>>> missed?
>>>> Thank you.
>>>>
>>>> Zhengchao Shao
>>>
>>> Hi Zhengchao,
>>>
>>> I failed to reproduce this large regression. Could you please share some
>>> information about your test environment?
>>>
>> Hi Wen Gu:
>>> - The nginx configure.
>> See the nginx.conf file in the attachment.
>>> - The guest(VM) cpu topology.
>> See the vm_cpuinfo file in the attachment.
>>> - The host(physical machine) cpu topology.
>> See the host_cpuinfo file in the attachment.
>>> - The mapping relationship between vcpu of guest(VM) and physical cpu 
>>> of host.
>> See the cpu_map file in the attachment.
>>> - The cpu usage (top) when regression happens.
>>>
>> See the perf_top and perf.svg file in the attachment.
> 
> Hi Zhengchao,
> 
> Thank you for the detailed information.
> 
> In the flame graph you provided, there are clearly prolonged spin-wait in
> both smc_rx_recvmsg and smc_tx_sendmsg. The footprint involves the
> __check_object_size() and find_vmap_area(). I think the regression relates
> to the spin lock contention when CONFIG_HARDENED_USERCOPY is set and Tx 
> / Rx
> concurrently copy data between userspace and kernel vzalloced DMB.
> 
>        App1           App2
>          |              ^
>          |              |  userspace
>       ----------------------
>          |    +-----+   |  kernel
>          +--->| DMB |---+
>               +-----+
> 
> - smc_tx_sendmsg -> memcpy_from_msg -> copy_from_iter -> check_copy_size ->
>    check_object_size -> check_heap_object -> if(vm) find_vmap_area -> 
> try to hold spin lock vmap_area_lock
> 
> - smc_rx_recvmsg -> memcpy_to_msg -> copy_to_iter -> check_copy_size ->
>    check_object_size -> check_heap_object -> if(vm) find_vmap_area -> 
> try to hold spin lock vmap_area_lock
> 
> So I reproduced your test (thanks again for the details) and changed the 
> DMB
> creation from vzalloc to kzalloc(or alloc_page), thereby avoiding the 
> spin lock
> contention in find_vmap_area. Then the regression disappears.
> (The attachments include flame graphs that use vzalloc and kzalloc 
> respectively.)
> 
>                        SMC
> -c1000 -t8      615397.66
> -c1000 -t96     625627.69
> 
> diff --git a/net/smc/smc_loopback.c b/net/smc/smc_loopback.c
> index 909c0699e91c..d6c9cd1a2f5b 100644
> --- a/net/smc/smc_loopback.c
> +++ b/net/smc/smc_loopback.c
> @@ -191,7 +191,9 @@ static int smc_lo_register_dmb(struct smcd_dev 
> *smcd, struct smcd_dmb *dmb,
>          }
> 
>          dmb_node->sba_idx = sba_idx;
> -       dmb_node->cpu_addr = vzalloc(dmb->dmb_len);
> +       dmb_node->cpu_addr = kzalloc(dmb->dmb_len, GFP_KERNEL |
> +                       __GFP_NOWARN | __GFP_NORETRY |
> +                       __GFP_NOMEMALLOC);
>          if (!dmb_node->cpu_addr) {
>                  rc = -ENOMEM;
>                  goto err_node;
> @@ -260,7 +262,7 @@ static int smc_lo_unregister_dmb(struct smcd_dev 
> *smcd, struct smcd_dmb *dmb)
>          write_unlock(&ldev->dmb_ht_lock);
> 
>          clear_bit(dmb_node->sba_idx, ldev->sba_idx_mask);
> -       vfree(dmb_node->cpu_addr);
> +       kfree(dmb_node->cpu_addr);
>          kfree(dmb_node);
>          SMC_LO_STAT_DMBS_DEC(ldev);
> 
> 
> Hope this works for you. And it needs to reconsider if the virtual alloced
> memory is the right way for DMB in loopback-ism.
> 
Hi Wen Gu：
	This patch works in my VM. Thank you for your support. And,
will this change take into your patchset?
Thanks very much.

Zhengchao Shao
> Best regards,
> Wen Gu
> 
>>> Thank you.
>>>
>>
>> Thank you very much.
>>
>> Zhengchao Shao

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