sys_rt_sigreturn calling sys_futex?

sys_rt_sigreturn calling sys_futex?

[Ivan Novick]

Hello,

I have a userspace app that I profiled using SystemTap.

It says there are frequent calls to sys_futex which come from sys_rt_sigreturn.

It is true, that my app has many signal handler calls due to
frequently set timers in the code.

I had a look at the source for my kernel: Suse: linux-2.6.27.39-0.3
but I don't see any calls to futex from inside sys_rt_sigreturn.

Do you know if sys_rt_sigreturn is somehow calling sys_futex?

And if so, does this imply that ultra-frequent signal handling can
create a bottleneck between many processes in the sys_rt_sigreturn
system call trying to access a futex?

Thank you and regards,
Ivan Novick

Re: sys_rt_sigreturn calling sys_futex?

[Thomas Gleixner]

On Fri, 22 Jan 2010, Ivan Novick wrote:
> Hello,
> 
> I have a userspace app that I profiled using SystemTap.
> 
> It says there are frequent calls to sys_futex which come from sys_rt_sigreturn.
> 
> It is true, that my app has many signal handler calls due to
> frequently set timers in the code.
> 
> I had a look at the source for my kernel: Suse: linux-2.6.27.39-0.3
> but I don't see any calls to futex from inside sys_rt_sigreturn.
> 
> Do you know if sys_rt_sigreturn is somehow calling sys_futex?

Well, it is not calling sys_futex, it is resuming the sys_futex
syscall which was interrupted by the signal. When the signal handler
returns it returns to the system call automatically.
 
Thanks,

	tglx