Date: Wed, 27 Dec 2023 09:58:31 +0800
From: Wen Gu <guwen@...ux.alibaba.com>
To: shaozhengchao <shaozhengchao@...wei.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 2023/12/27 09:12, shaozhengchao wrote:
> 
> 
> 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.
> 

Yes, the regression caused by vzalloced DMB in concurrency scenarios will
be handled in my following patchset. But whether in this way I need to think
about it, since physical contiguous memory is expensive.

Best regards,
Wen Gu

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

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