Re: [Xen-devel] [PATCH v2 19/23] x86: PIT emulation is common to both PV and HVM

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Aug 28, 2018 at 09:04:24AM -0600, Jan Beulich wrote:
> >>> On 28.08.18 at 16:58, <wei.liu2@xxxxxxxxxx> wrote:
> > On Tue, Aug 28, 2018 at 03:51:51PM +0100, Andrew Cooper wrote:
> >> On 28/08/18 15:48, Wei Liu wrote:
> >> > On Tue, Aug 28, 2018 at 08:36:37AM -0600, Jan Beulich wrote:
> >> >>>>> On 28.08.18 at 15:19, <wei.liu2@xxxxxxxxxx> wrote:
> >> >>> On Tue, Aug 28, 2018 at 05:44:51AM -0600, Jan Beulich wrote:
> >> >>>>>>> On 26.08.18 at 14:19, <wei.liu2@xxxxxxxxxx> wrote:
> >> >>>>> Move the file to x86 common code and change its name to emul-i8254.c.
> >> >>>>>
> >> >>>>> Put HVM only code under CONFIG_HVM or is_hvm_domain.
> >> >>>>>
> >> >>>>> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> >> >>>>> ---
> >> >>>>> v2: move the whole file.
> >> >>>>> ---
> >> >>>>>  xen/arch/x86/Makefile     |   1 +-
> >> >>>>>  xen/arch/x86/emul-i8254.c | 609 
> >> >>>>> +++++++++++++++++++++++++++++++++++++++-
> >> >>>>>  xen/arch/x86/hvm/Makefile |   1 +-
> >> >>>>>  xen/arch/x86/hvm/i8254.c  | 597 
> >> >>>>> +--------------------------------------
> >> >>>>>  4 files changed, 610 insertions(+), 598 deletions(-)
> >> >>>>>  create mode 100644 xen/arch/x86/emul-i8254.c
> >> >>>>>  delete mode 100644 xen/arch/x86/hvm/i8254.c
> >> >>>> On the assumption that the changes to the file are only CONFIG_HVM
> >> >>>> additions
> >> >>> No only that. There are a few is_hvm_domain calls as well.
> >> >>>
> >> >>>> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
> >> >>> Does this still stand?
> >> >> Yes, albeit looking at the full diff of the files I'm then a little
> >> >> puzzled about is_hvm_domain() uses: Why does pit_load_count()
> >> >> need an #ifdef added at all, with the is_hvm_vcpu() check
> >> >> right before it?
> >> > Because if I don't do that we get "defined but not used" warnings.
> >> 
> >> (hopefully) not with the newer is_hvm_vcpu() which evaluates its
> >> arguments properly.
> > 
> > The real reason is I put pit_time_fired under CONFIG_HVM because it is
> > only used as a HVM only callback -- passed as a parameter to
> > create_periodic_time.
> > 
> > If I remove CONFIG_HVM around pit_time_fired, I can remove CONFIG_HVM in
> > pit_load_count.  Let me know if you prefer this.
> 
> Oh, I see. I'd prefer this, yes, but I'm unconvinced DCE would
> eliminate pit_time_fired() in that case. If you find it does, I think
> that would be better indeed (less #ifdef clutter).

At least for gcc 6.3 DCE does eliminate pit_time_fired. I will remove
the two CONFIG_HVMs in the next iteration.

Wei.

> 
> Jan
> 
> 

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