Re: [Xen-devel] [PATCH] x86 hvm: freeze PIT/LAPIC timer emulation while its IRQ is masked

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 10/09/2009 10:54, "Kouya Shimura" <kouya@xxxxxxxxxxxxxx> wrote:

>> Not using pt_irq_masked() seems odd. Is it to avoid 859 IRQ mask checks, and
>> if so why are you doing that? Why do we care that rombios twiddles the 8259
>> masks a bunch during boot?
> 
> I guessed that the cost of freezing/thawing a timer with the 8259 mask
> is higher than timer emulation.  And the PIT timer is actually active
> while rombios masks the 8259.
> 
> If using pt_irq_masked() is desirable, I'll remake it.

If your patch works without even any theoretical lost of correctness, then
that makes it more attractive, obviously.

Some evidence that the cost saving is at all measurable would also be good.
Premature optimisation being evil, etc. ;-)

 -- Keir



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel