Re: [PATCH 1/4] apic: add support for x2APIC mode

[Igor Mammedov]

On Sat, 25 Feb 2023 17:15:17 +0700
Bui Quang Minh <minhquangbui99@gmail.com> wrote:

> On 2/24/23 21:29, Igor Mammedov wrote:
> > On Tue, 21 Feb 2023 23:04:57 +0700
> > Bui Quang Minh <minhquangbui99@gmail.com> wrote:
> >   
> >> This commit refactors APIC registers read/write function to support both
> >> MMIO read/write in xAPIC mode and MSR read/write in x2APIC mode. Also,
> >> support larger APIC ID, self IPI, new IPI destination determination in
> >> x2APIC mode.
> >>
> >> Signed-off-by: Bui Quang Minh <minhquangbui99@gmail.com>
> >> ---
> >>   hw/intc/apic.c                  | 211 +++++++++++++++++++++++++-------
> >>   hw/intc/apic_common.c           |   2 +-
> >>   include/hw/i386/apic.h          |   5 +-
> >>   include/hw/i386/apic_internal.h |   2 +-
> >>   4 files changed, 172 insertions(+), 48 deletions(-)
> >>
> >> diff --git a/hw/intc/apic.c b/hw/intc/apic.c
> >> index 2d3e55f4e2..205d5923ec 100644
> >> --- a/hw/intc/apic.c
> >> +++ b/hw/intc/apic.c
> >> @@ -30,6 +30,7 @@
> >>   #include "hw/i386/apic-msidef.h"
> >>   #include "qapi/error.h"
> >>   #include "qom/object.h"
> >> +#include "tcg/helper-tcg.h"
> >>   
> >>   #define MAX_APICS 255  
> > 
> > I'm curious how does it work without increasing ^^^?  
> 
> Hmm, my commit message is not entirely correct. In this series, some 
> operations (send IPI, IPI destination determination) have been updated 
> to support x2APIC mode. However, the emulated APIC still doesn't support 
> APIC ID larger than 255 because currently, we use a fixed length (255 + 
> 1) array to manage local APICs. So to support larger APIC ID, I think we 
> need to find any way to manage those, as the possible allocated APIC ID 
> range is large and maybe the allocated APIC ID is sparse which makes 
> fixed length array so wasteful.
how much sparse it is? 

benefits of simple static array is simplicity in management and O(1) access 
time.
QEMU does know in advance max apic id so we can size array by dynamically
allocating it when 1st apic is created. Or if IDs are too sparse
switch to another structure to keep mapping.


> 
> Thanks,
> Quang Minh.
>