Re: [Xen-devel] [PATCH] xen: privcmd: schedule() after private hypercall when non CONFIG_PREEMPT

[Luis R. Rodriguez]

On Tue, Dec 02, 2014 at 11:11:18AM +0000, David Vrabel wrote:
> On 01/12/14 22:36, Luis R. Rodriguez wrote:
> > 
> > Then I do agree its a fair analogy (and find this obviously odd that how
> > widespread cond_resched() is), we just don't have an equivalent for IRQ
> > context, why not avoid the special check then and use this all the time in the
> > middle of a hypercall on the return from an interrupt (e.g., the timer
> > interrupt)?
> 
> http://lists.xen.org/archives/html/xen-devel/2014-02/msg01101.html

OK thanks! That explains why we need some asm code but in that submission you
still also had used is_preemptible_hypercall(regs) and in the new
implementation you use a CPU variable xen_in_preemptible_hcall prior to calling
preempt_schedule_irq(). I believe you added the CPU variable because
preempt_schedule_irq() will preempt first without any checks if it should, I'm
asking why not do something like cond_resched_irq() where we check with
should_resched() prior to preempting and that way we can avoid having to use
the CPU variable?

  Luis
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