Re: [PATCH 4/6] kvm tools: Add rwlock wrapper

[Ingo Molnar <mingo@elte.hu>]

* Ingo Molnar <mingo@elte.hu> wrote:

> > This code is very much tied with the kernel scheduler. [...]
> 
> It would not be particularly complex to enable user-space to 
> request a callback on context switch events.
> 
> I was thinking on and off about allowing perf events to generate a 
> per sampling event notification signal on specific events, such as 
> page faults or context switches.

I was thinking about that on and off so loudly that Peter implemented 
it long ago via fasync support on the perf event fd! :-)

So if you set a notification signal via fcntl(F_SETOWN) on the 
scheduler context switch event fd, the user-space RCU code will get a 
signal on every context switch.

I have not tried it for this purpose yet, so let us know if there are 
unexpected complications :)

Thanks,

	Ingo