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SubjectRe: [init/console] a91bd6223e: unixbench.score -5.9% regression
Hello,

just for record.

On Tue 2021-02-09 13:49:25, kernel test robot wrote:
>
> Greeting,
>
> FYI, we noticed a -5.9% regression of unixbench.score due to commit:
>
>
> commit: a91bd6223ecd46addc71ee6fcd432206d39365d2 ("Revert "init/console: Use ttynull as a fallback when there is no console"")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>
>
> in testcase: unixbench
> on test machine: 16 threads Intel(R) Xeon(R) E-2278G CPU @ 3.40GHz with 32G memory
> with following parameters:
>
> runtime: 300s
> nr_task: 30%
> test: dhry2reg
> cpufreq_governor: performance
> ucode: 0xde
>
> test-description: UnixBench is the original BYTE UNIX benchmark suite aims to test performance of Unix-like system.
> test-url: https://github.com/kdlucas/byte-unixbench
>
>
>
> If you fix the issue, kindly add following tag
> Reported-by: kernel test robot <oliver.sang@intel.com>
>
>
> 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 split-job --compatible job.yaml
> bin/lkp run compatible-job.yaml
>
> =========================================================================================
> compiler/cpufreq_governor/kconfig/nr_task/rootfs/runtime/tbox_group/test/testcase/ucode:
> gcc-9/performance/x86_64-rhel-8.3/30%/debian-10.4-x86_64-20200603.cgz/300s/lkp-cfl-e1/dhry2reg/unixbench/0xde
>
> commit:
> c4cc3b1de3 ("Merge tag 'gcc-plugins-v5.11-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux")
> a91bd6223e ("Revert "init/console: Use ttynull as a fallback when there is no console"")
>
> c4cc3b1de31b76f4 a91bd6223ecd46addc71ee6fcd4
> ---------------- ---------------------------
> fail:runs %reproduction fail:runs
> | | |
> 0:4 2% 0:4 perf-profile.children.cycles-pp.error_entry
> %stddev %change %stddev
> \ | \
> 19487 -5.9% 18336 unixbench.score
> 8.875e+10 -5.9% 8.351e+10 unixbench.workload
> 0.50 +0.1 0.61 ± 3% mpstat.cpu.all.irq%
> 44280 ± 4% +15.9% 51322 ± 3% softirqs.CPU0.SCHED
> 29624 ± 3% +9.6% 32476 vmstat.system.in

> 2207 ±1927% +3559.5% 80796 ± 18% sched_debug.cfs_rq:/.spread0.avg
> 135343 ± 38% +61.1% 218075 ± 16% sched_debug.cfs_rq:/.spread0.max
> 0.01 ± 31% +78.3% 0.01 ± 22% perf-sched.sch_delay.avg.ms.do_nanosleep.hrtimer_nanosleep.__x64_sys_nanosleep.do_syscall_64
> 0.01 ± 7% +22.8% 0.02 ± 2% perf-sched.sch_delay.avg.ms.do_task_dead.do_exit.do_group_exit.__x64_sys_exit_group.do_syscall_64
> 0.02 ± 15% +27.1% 0.02 ± 11% perf-sched.sch_delay.avg.ms.do_wait.kernel_wait4.__do_sys_wait4.do_syscall_64
> 0.02 ± 44% +113.3% 0.04 ± 12% perf-sched.sch_delay.avg.ms.exit_to_user_mode_prepare.syscall_exit_to_user_mode.entry_SYSCALL_64_after_hwframe.[unknown]
> 0.02 ± 10% +56.1% 0.03 ± 25% perf-sched.sch_delay.avg.ms.schedule_hrtimeout_range_clock.poll_schedule_timeout.constprop.0.do_select
> 0.02 ± 44% +113.3% 0.04 ± 12% perf-sched.sch_delay.max.ms.exit_to_user_mode_prepare.syscall_exit_to_user_mode.entry_SYSCALL_64_after_hwframe.[unknown]
> 0.01 ± 11% +37.5% 0.01 ± 19% perf-sched.total_sch_delay.average.ms
> 2001 +120.7% 4416 ± 33% perf-sched.wait_and_delay.max.ms.do_task_dead.do_exit.do_group_exit.__x64_sys_exit_group.do_syscall_64
> 0.05 ± 54% +56.5% 0.08 ± 7% perf-sched.wait_time.avg.ms.schedule_timeout.khugepaged.kthread.ret_from_fork
> 2001 +120.7% 4416 ± 33% perf-sched.wait_time.max.ms.do_task_dead.do_exit.do_group_exit.__x64_sys_exit_group.do_syscall_64
> 0.05 ± 54% +56.5% 0.08 ± 7% perf-sched.wait_time.max.ms.schedule_timeout.khugepaged.kthread.ret_from_fork

> 0.07 ±173% +0.2 0.27 ± 21% perf-profile.children.cycles-pp.io_serial_in
> 0.07 ±173% +0.2 0.30 ± 21% perf-profile.children.cycles-pp.serial8250_console_putchar
> 0.07 ±173% +0.2 0.31 ± 20% perf-profile.children.cycles-pp.wait_for_xmitr
> 0.08 ±173% +0.2 0.32 ± 21% perf-profile.children.cycles-pp.uart_console_write
> 0.08 ±173% +0.2 0.33 ± 21% perf-profile.children.cycles-pp.serial8250_console_write
> 0.09 ±173% +0.2 0.33 ± 22% perf-profile.children.cycles-pp.asm_sysvec_irq_work
> 0.09 ±173% +0.2 0.33 ± 22% perf-profile.children.cycles-pp.sysvec_irq_work
> 0.09 ±173% +0.2 0.33 ± 22% perf-profile.children.cycles-pp.__sysvec_irq_work
> 0.09 ±173% +0.2 0.33 ± 22% perf-profile.children.cycles-pp.irq_work_run
> 0.09 ±173% +0.2 0.33 ± 22% perf-profile.children.cycles-pp.irq_work_single
> 0.09 ±173% +0.2 0.33 ± 22% perf-profile.children.cycles-pp.printk
> 0.09 ±173% +0.2 0.33 ± 22% perf-profile.children.cycles-pp.vprintk_emit
> 0.09 ±173% +0.2 0.33 ± 22% perf-profile.children.cycles-pp.console_unlock
> 0.09 ±173% +0.3 0.34 ± 24% perf-profile.children.cycles-pp.irq_work_run_list

The commit fixed regression in registration of console drivers.
A console was likely not registered before and saved some cycles.
But people want consoles ;-)

By other words, this regression is kind of expected.

Best Regards,
Petr

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