linux-kernel - Re: [PATCH RFC] paravirt_ops: refactor struct paravirt_ops into smaller pv_*

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Date:	Fri, 28 Sep 2007 17:40:30 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"Nakajima, Jun" <jun.nakajima@...el.com>
CC:	Andi Kleen <ak@...e.de>, Zachary Amsden <zach@...are.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Avi Kivity <avi@...ranet.com>,
	Glauber de Oliveira Costa <glommer@...il.com>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH RFC] paravirt_ops: refactor struct paravirt_ops into smaller
 pv_*_ops

Nakajima, Jun wrote:
> Yes. For the native, "safe_halt" is "sti; hlt". The "native_halt" is
> just "hlt". So the para_virt part of "hlt" could be moved to pv_cpu_ops,
> and the "sti" part stays in pv_irq_ops.
>   

By "sti part", you mean the full "sti; hlt" sequence of safe_halt,
right?  Since it needs to be an atomic sequence to avoid race
conditions, so the native sequence has to be precisely "sti; hlt" to
take advantage of the sti shadow, and other pv-backends will need their
own way to guarantee this atomicity.

But I'm quite happy to put plain "hlt" into cpu_ops as halt_cpu() or
something (and perhaps rename safe_halt to something a bit more
descriptive).

> Actually my concern was that such misc ops might grow to include the
> things don't fit well anywhere else. To me, then pv_lazy_ops (with just
> .set_mode) might be better.
>   

The lazy interface has needed a rethink anyway.

    J
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