Re: [PATCH 0/2] tools perf: Add a new benchmark tool for semaphore/mutex

[Ingo Molnar <mingo@kernel.org>]

* Chen, Dennis (SRDC SW) <Dennis1.Chen@amd.com> wrote:

> <PATCH PREFACE>
> -------------------
> This patch series are used to add a new performance benchmark tool for semaphore or mutex:
> The new tool will fork NR tasks specified through the command line and bind each of them
> to every CPUs in the system equally. The command to launch the tool looks like:
> '# perf bench locking mutex -p 8 -t 400 -c'
> 
> The above command will create 400 tasks in a system with 8-CPU, each CPU will have 50 tasks.
> After the task be created, it will read all the files and directories in '/sys/module'.
> sysfs is RAM based and its read operation for both dir and file is very sensitive for mutex
> lock, also '/sys/module' has almost no dependencies on external devices.
> 
> We can use this tool with 'perf record' command to get the hot-spot of the codes or 
> 'perf top -g' to get live info, for example, below is a test case run in a intel i7-2600 box
> (-c option is to get the cpu cycles, I don't use it in this test case):
> 
> # perf record -a perf bench locking mutex -p 8 -t 4000
> # Running locking/mutex benchmark... 
>  ...
>  [13894 ]/6  duration        23 s   609392 us
>  [13996 ]/4  duration        23 s   599418 us
>  [14056 ]/0  duration        23 s   595710 us
>  [13715 ]/3  duration        23 s   621719 us
>  [13390 ]/6  duration        23 s   644020 us
>  [13696 ]/0  duration        23 s   623101 us
>  [14334 ]/6  duration        23 s   580262 us
>  [14343 ]/7  duration        23 s   578702 us
>  [14283 ]/3  duration        23 s   583007 us
>  -----------------------------------
>  Total duration     79353 s   943945 us
> 
>  real: 23.84   s
>  user: 0.00   
>  sys:  0.45   
> 
> # perf report
> ===================================================================================
> ...
> # perf version : 3.3.2
> # arch : x86_64
> # nrcpus online : 8
> # nrcpus avail : 8
> # cpudesc : Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz
> # total memory : 3966460 kB
> # cmdline : /usr/bin/perf record -a perf bench locking mutex -p 8 -t 4000
> 
> # Events: 131K cycles
> #
> # Overhead          Command                      Shared Object                                 Symbol
> # ........  ...............  .................................  .....................................
> #
>     22.12%           perf  [kernel.kallsyms]                  [k] __mutex_lock_slowpath
>      8.27%           perf  [kernel.kallsyms]                  [k] _raw_spin_lock
>      6.16%           perf  [kernel.kallsyms]                  [k] mutex_unlock
>      5.22%           perf  [kernel.kallsyms]                  [k] mutex_spin_on_owner
>      4.94%           perf  [kernel.kallsyms]                  [k] sysfs_refresh_inode
>      4.82%           perf  [kernel.kallsyms]                  [k] mutex_lock
>      2.67%           perf  [kernel.kallsyms]                  [k] __mutex_unlock_slowpath
>      2.61%           perf  [kernel.kallsyms]                  [k] link_path_walk
>      2.42%           perf  [kernel.kallsyms]                  [k] _raw_spin_lock_irqsave
>      1.61%           perf  [kernel.kallsyms]                  [k] __d_lookup
>      1.18%           perf  [kernel.kallsyms]                  [k] clear_page_c
>      1.16%           perf  [kernel.kallsyms]                  [k] dput
>      0.97%           perf  [kernel.kallsyms]                  [k] do_lookup
>      0.93%        swapper  [kernel.kallsyms]                  [k] intel_idle
>      0.87%           perf  [kernel.kallsyms]                  [k] get_page_from_freelist
>      0.85%           perf  [kernel.kallsyms]                  [k] __strncpy_from_user
>      0.81%           perf  [kernel.kallsyms]                  [k] system_call
>      0.78%           perf  libc-2.13.so                       [.] 0x84ef0         
>      0.71%           perf  [kernel.kallsyms]                  [k] vfsmount_lock_local_lock
>      0.68%           perf  [kernel.kallsyms]                  [k] sysfs_dentry_revalidate
>      0.62%           perf  [kernel.kallsyms]                  [k] try_to_wake_up
>      0.62%           perf  [kernel.kallsyms]                  [k] kfree
>      0.60%           perf  [kernel.kallsyms]                  [k] kmem_cache_alloc   
> ............................................................................................
> 

Nice! Would be nice to lift some of this information over into 
the changelogs, to address my complaints in the previous mail.

> We can see that for 4000 tasks running in 8 CPUs simultaneously, it will create a very heavy 
> contention for the mutex lock, so lot's of tasks enter into the slow path of the mutex lock...
> I am very curious if we switch the mutex to the semaphore in this case, how's thing going? 
> My next plan

Seems like an unfinished sentence.

Thanks,

	Ingo