Re: [PATCH 1/3] sched: add sched_task_call()

Josh Poimboeuf
2015-02-19T17:04:25Z

On Thu, Feb 19, 2015 at 05:33:59PM +0100, Vojtech Pavlik wrote:
> On Thu, Feb 19, 2015 at 10:24:29AM -0600, Josh Poimboeuf wrote:
>
> > > No, these tasks will _never_ make syscalls. So you need to guarantee
> > > they don't accidentally enter the kernel while you flip them. Something
> > > like so should do.
> > >
> > > You set TIF_ENTER_WAIT on them, check they're still in userspace, flip
> > > them then clear TIF_ENTER_WAIT.
> >
> > Ah, that's a good idea. But how do we check if they're in user space?
>
> I don't see the benefit in holding them in a loop - you can just as well
> flip them from the syscall code as kGraft does.

But we were talking specifically about HPC tasks which never make
syscalls.

--
Josh