Re: [Qemu-devel] [PATCH v3 1/3] qemu-thread: introduce qemu-thread-common.[ch]

["Emilio G. Cota" <cota@braap.org>]

On Fri, Apr 20, 2018 at 12:42:10 +0800, Peter Xu wrote:
> Put all the shared qemu-thread implementations into these files.  The
> header should be internal to qemu-thread but not for qemu-thread users.
> 
> Introduce some hooks correspondingly for the shared part.  Note that in
> qemu_mutex_unlock_impl() we moved the call before unlock operation which
> should make more sense.  And we don't need qemu_mutex_post_unlock() hook.
> 
> Currently the hooks only calls the tracepoints.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
(snip)
> -    trace_qemu_mutex_lock(mutex, file, line);
> -
> +    qemu_mutex_pre_lock(mutex, file, line);
>      err = pthread_mutex_lock(&mutex->lock);
>      if (err)
>          error_exit(err, __func__);
> -
> -    trace_qemu_mutex_locked(mutex, file, line);
> +    qemu_mutex_post_lock(mutex, file, line);
>  }

I see the value in consolidating these calls. However, having a separate
object means that this adds two function calls to mutex_lock. This
significantly reduces performance, even without --enable-debug-mutex:
- Before:
$ taskset -c 0 tests/atomic_add-bench -n 1 -m
Parameters:
 # of threads:      1
 duration:          1
 ops' range:        1024
Results:
Duration:            1 s
 Throughput:         57.24 Mops/s
 Throughput/thread:  57.24 Mops/s/thread

- After:
$ taskset -c 0 tests/atomic_add-bench -n 1 -m
Parameters:
 # of threads:      1
 duration:          1
 ops' range:        1024
Results:
Duration:            1 s
 Throughput:         49.22 Mops/s
 Throughput/thread:  49.22 Mops/s/thread

So either inlines/macros should be used instead -- I'd prefer
inlines but I'm not sure they'll work with the tracing calls.

I think you should cherry-pick this patch[1] and add it to the
series -- it'll let you make sure the series does not affect
performance.

Cheers,

		Emilio

[1] https://github.com/cota/qemu/commit/f04f34df