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Subject: Re: [bpf] will-it-scale.per_thread_ops 2.6% improvement
To:     kernel test robot <rong.a.chen@intel.com>
CC:     Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andriin@fb.com>,
        LKML <linux-kernel@vger.kernel.org>, <lkp@lists.01.org>
References: <20200627082222.GG5535@shao2-debian>
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On 6/27/20 1:22 AM, kernel test robot wrote:
> Greeting,
> 
> FYI, we noticed a 2.6% improvement of will-it-scale.per_thread_ops due to commit:

Thanks. The improvement is always good although I do not know
what will-it-scale.per_thread_ops exactly running.

But I think the commit
    492e639f0c222784e2e0f121966375f641c61b15 ("bpf: Add bpf_seq_printf 
and bpf_seq_write helpers")
probably not the reason for the improvement. This patch just add bpf 
helpers and they should not be called in normal user codes.

If you want to identify which commit is responsible for the improvement,
you probably want to double check.

> 
> 
> commit: 492e639f0c222784e2e0f121966375f641c61b15 ("bpf: Add bpf_seq_printf and bpf_seq_write helpers")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> 
> in testcase: will-it-scale
> on test machine: 288 threads Intel(R) Xeon Phi(TM) CPU 7295 @ 1.50GHz with 80G memory
> with following parameters:
> 
> 	nr_task: 100%
> 	mode: thread
> 	test: pthread_mutex2
> 	cpufreq_governor: performance
> 	ucode: 0x11
> 
> test-description: Will It Scale takes a testcase and runs it from 1 through to n parallel copies to see if the testcase will scale. It builds both a process and threads based test in order to see any differences between the two.
> test-url: https://github.com/antonblanchard/will-it-scale
> 
> In addition to that, the commit also has significant impact on the following tests:
> 
> +------------------+----------------------------------------------------------------------+
> | testcase: change | will-it-scale: will-it-scale.per_process_ops 2.5% improvement        |
> | test machine     | 288 threads Intel(R) Xeon Phi(TM) CPU 7295 @ 1.50GHz with 80G memory |
> | test parameters  | cpufreq_governor=performance                                         |
> |                  | mode=process                                                         |
> |                  | nr_task=100%                                                         |
> |                  | test=malloc2                                                         |
> |                  | ucode=0x11                                                           |
> +------------------+----------------------------------------------------------------------+
> 
> 
> 
> 
> Details are as below:
> -------------------------------------------------------------------------------------------------->
> 
> 
> To reproduce:
> 
>          git clone https://github.com/intel/lkp-tests.git
>          cd lkp-tests
>          bin/lkp install job.yaml  # job file is attached in this email
>          bin/lkp run     job.yaml
> 
> =========================================================================================
> compiler/cpufreq_governor/kconfig/mode/nr_task/rootfs/tbox_group/test/testcase/ucode:
>    gcc-7/performance/x86_64-rhel-7.6/thread/100%/debian-x86_64-20191114.cgz/lkp-knm01/pthread_mutex2/will-it-scale/0x11
> 
> commit:
>    b121b341e5 ("bpf: Add PTR_TO_BTF_ID_OR_NULL support")
>    492e639f0c ("bpf: Add bpf_seq_printf and bpf_seq_write helpers")
> 
> b121b341e5983bdc 492e639f0c222784e2e0f121966
> ---------------- ---------------------------
>           %stddev     %change         %stddev
>               \          |                \
>     6105969            +2.6%    6265564        will-it-scale.per_thread_ops
>        9855         +1196.5%     127775 ± 92%  will-it-scale.time.maximum_resident_set_size
>   1.759e+09            +2.6%  1.804e+09        will-it-scale.workload
[...]
> 
> 
> ***************************************************************************************************
> lkp-knm01: 288 threads Intel(R) Xeon Phi(TM) CPU 7295 @ 1.50GHz with 80G memory
> =========================================================================================
> compiler/cpufreq_governor/kconfig/mode/nr_task/rootfs/tbox_group/test/testcase/ucode:
>    gcc-9/performance/x86_64-rhel-7.6/thread/100%/debian-x86_64-20191114.cgz/lkp-knm01/context_switch1/will-it-scale/0x11
> 
> commit:
>    b121b341e5 ("bpf: Add PTR_TO_BTF_ID_OR_NULL support")
>    492e639f0c ("bpf: Add bpf_seq_printf and bpf_seq_write helpers")
> 
> b121b341e5983bdc 492e639f0c222784e2e0f121966
> ---------------- ---------------------------
>         fail:runs  %reproduction    fail:runs
>             |             |             |
>            2:2         -100%            :2     dmesg.WARNING:at#for_ip_swapgs_restore_regs_and_return_to_usermode/0x
>            2:2         -100%            :2     dmesg.WARNING:stack_recursion
> 
> 
> 
> 
> 
> Disclaimer:
> Results have been estimated based on internal Intel analysis and are provided
> for informational purposes only. Any difference in system hardware or software
> design or configuration may affect actual performance.
> 
> 
> Thanks,
> Rong Chen
>