Re: [PATCH 0/5] lockdep: Add information of file and line to lockdep_map

[Hitoshi Mitake]

On 2010å01æ13æ 18:52, Peter Zijlstra wrote:
> On Thu, 2010-01-07 at 19:39 +0900, Hitoshi Mitake wrote:
> > There are a lot of lock instances with same names (e.g. port_lock).
> > This patch series add __FILE__ and __LINE__ to lockdep_map,
> > and these will be used for trace lock events.
> >
> > Example use from perf lock map:
> >
> > | 0xffffea0004c992b8: __pte_lockptr(page) (src: include/linux/mm.h, line: 952)
> > | 0xffffea0004b112b8: __pte_lockptr(page) (src: include/linux/mm.h, line: 952)
> > | 0xffffea0004a3f2b8: __pte_lockptr(page) (src: include/linux/mm.h, line: 952)
> > | 0xffffea0004cd5228: __pte_lockptr(page) (src: include/linux/mm.h, line: 952)
> > | 0xffff8800b91e2b28:&sb->s_type->i_lock_key (src: fs/inode.c, line: 166)
> > | 0xffff8800bb9d7ae0: key (src: kernel/wait.c, line: 16)
> > | 0xffff8800aa07dae0:&dentry->d_lock (src: fs/dcache.c, line: 944)
> > | 0xffff8800b07fbae0:&dentry->d_lock (src: fs/dcache.c, line: 944)
> > | 0xffff8800b07f3ae0:&dentry->d_lock (src: fs/dcache.c, line: 944)
> > | 0xffff8800bf15fae0:&sighand->siglock (src: kernel/fork.c, line: 1490)
> > | 0xffff8800b90f7ae0:&dentry->d_lock (src: fs/dcache.c, line: 944)
> > | ...
> >
> > (This output of perf lock map is produced by my local version,
> >   I'll send this later.)
> >
> > And sadly, as Peter Zijlstra predicted, this produces certain overhead.
> >
> > Before appling this series:
> > | % sudo ./perf lock rec perf bench sched messaging
> > | # Running sched/messaging benchmark...
> > | # 20 sender and receiver processes per group
> > | # 10 groups == 400 processes run
> > |
> > |      Total time: 3.834 [sec]
> > After:
> >   sudo ./perf lock rec perf bench sched messaging
> > | # Running sched/messaging benchmark...
> > | # 20 sender and receiver processes per group
> > | # 10 groups == 400 processes run
> > |
> > |      Total time: 5.415 [sec]
> > | [ perf record: Woken up 0 times to write data ]
> > | [ perf record: Captured and wrote 53.512 MB perf.data (~2337993 samples) ]
> >
> > But raw exec of perf bench sched messaging is this:
> > | % perf bench sched messaging
> > | # Running sched/messaging benchmark...
> > | # 20 sender and receiver processes per group
> > | # 10 groups == 400 processes run
> > |
> > |      Total time: 0.498 [sec]
> >
> > Tracing lock events already produces amount of overhead.
> > I think the overhead produced by this series is not a fatal problem,
> > radically optimization is required...
>
> Right, these patches look OK, for the tracing overhead, you could
> possibly hash the file:line into a u64 and reduce the tracepoint size,
> that should improve the situation I tihnk, because I seem to remember
> the only thing that really matters for speed is the size of things.

Thanks for your opinion, Peter.
I'll work on reducing size of events later. Hashing is a good idea.
I think indexing is also way to reduce size.

And I want lockdep_map to have another thing, type of lock.
For example, mutex and spinlock has completely different acquired time 
and attributes,
so I want to separate these things. If lockdep_map has member
to express type, things will be easy.

How do you think?
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