Re: [PATCH] perf lock: clean the options for perf record

[Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>]

On 2011年02月23日 13:17, Hitoshi Mitake wrote:
> On 2011年02月23日 03:22, Frederic Weisbecker wrote:
>> On Tue, Feb 22, 2011 at 04:43:35PM +0100, Peter Zijlstra wrote:
>>> On Wed, 2011-02-23 at 00:30 +0900, Hitoshi Mitake wrote:
>>>> How do you think about it?
>>>
>>> Most of the lock code (esp the spinlock stuff) is already way over the
>>> threshold of sanity, adding to that for some dubious reasons doesn't
>>> seem like a good idea.
>>>
>>> I'm still not at all sure why people want all this lock tracing.
>>
>> Right, well I can imagine many usecases that could make lock
>> tracing bring more value than what lockstat already provides,
>> through a tool like perf lock if we enhance it.
>>
>> We should probably first focus on developing the tooling side
>> and make it useful enough that optimizations in the kernel
>> side become desirable.
>>
>
> Yes, lockstat only provides the lock usage statistics of
> entire of the system. perf lock will be able to provide the partial
> information of specified term, or the degree of dependency
> between locks.
>

For trial, I created new tracepoint for rwsem and tested.
Names of events are rwsem_{acquire, contended, acquired, release},
their meanings are similar to lock_{...}.

I traced perf bench sched messaging and result was,

mitake@x201i:~/linux/.../tools/perf% ./perf bench sched messaging
# Running sched/messaging benchmark...
# 20 sender and receiver processes per group
# 10 groups == 400 processes run

      Total time: 1.252 [sec]
mitake@x201i:~/linux/.../tools/perf% sudo ./perf record -R -m 1024 -c 1 
-e rwsem:rwsem_acquire -e 
rwsem:rwsem_release,rwsem:rwsem_contended,rwsem:rwsem_acquired ./perf 
bench sched messaging
# Running sched/messaging benchmark...
# 20 sender and receiver processes per group
# 10 groups == 400 processes run

      Total time: 1.332 [sec]
[ perf record: Woken up 4 times to write data ]
[ perf record: Captured and wrote 13.495 MB perf.data (~589597 samples) ]

raw execution of sched messaging was 1.252 sec, and traced version
was 1.332 sec. This overhead is far smaller than the overhead of
current lock tracepoints.

I think that it is possible to write some meaningful tools
like reader/writer ratio measuring. If something can be written,
I'll post it.