Re: [PATCH v2 1/3] eal: add x86 cpuid support for monitorx

[David Marchand <david.marchand@redhat.com>]

On Thu, Apr 13, 2023 at 7:51 PM Tummala, Sivaprasad
<Sivaprasad.Tummala@amd.com> wrote:
>
> [AMD Official Use Only - General]
>
> Hi David,
>
> > -----Original Message-----
> > From: David Marchand <david.marchand@redhat.com>
> > Sent: Thursday, April 13, 2023 5:30 PM
> > To: Tummala, Sivaprasad <Sivaprasad.Tummala@amd.com>
> > Cc: david.hunt@intel.com; dev@dpdk.org; Thomas Monjalon
> > <thomas@monjalon.net>; Burakov, Anatoly <anatoly.burakov@intel.com>
> > Subject: Re: [PATCH v2 1/3] eal: add x86 cpuid support for monitorx
> >
> > Caution: This message originated from an External Source. Use proper caution
> > when opening attachments, clicking links, or responding.
> >
> >
> > On Thu, Apr 13, 2023 at 1:54 PM Sivaprasad Tummala
> > <sivaprasad.tummala@amd.com> wrote:
> > >
> > > Add a new CPUID flag to indicate support for monitorx instruction on
> > > AMD Epyc processors.
> > >
> > > Signed-off-by: Sivaprasad Tummala <sivaprasad.tummala@amd.com>
> > > ---
> > >  lib/eal/include/generic/rte_cpuflags.h | 2 ++
> > >  lib/eal/x86/include/rte_cpuflags.h     | 1 +
> > >  lib/eal/x86/rte_cpuflags.c             | 3 +++
> > >  3 files changed, 6 insertions(+)
> > >
> > > diff --git a/lib/eal/include/generic/rte_cpuflags.h
> > > b/lib/eal/include/generic/rte_cpuflags.h
> > > index d35551e931..db653a8dd7 100644
> > > --- a/lib/eal/include/generic/rte_cpuflags.h
> > > +++ b/lib/eal/include/generic/rte_cpuflags.h
> > > @@ -26,6 +26,8 @@ struct rte_cpu_intrinsics {
> > >         /**< indicates support for rte_power_pause function */
> > >         uint32_t power_monitor_multi : 1;
> > >         /**< indicates support for rte_power_monitor_multi function */
> > > +       uint32_t amd_power_monitorx : 1;
> > > +       /**< indicates amd support for rte_power_monitor function */
> >
> > I did not look at the patch detail, I just stopped at this part.
> > What makes the AMD monitorx stuff special that it needs to be exposed in the
> > generic API?
>
> Monitorx is different ISA /opcode (0F 01 FA) as compared to UMonitor (0F 01 C8). This need to be distinguished
> on specific x86 platforms. Hence in the current power intrinsics, for x86 we require a new flag to
> distinguish MonitorX and UMonitor and invoke the appropriate x86 ISA in the datapath.

Requiring a new x86 cpuflag to identify this ISA presence is ok.


But here, I am talking about the generic power instrinsic API.
Let me phrase my comment differently...

As described in the API:
        uint32_t power_monitor : 1;
        /**< indicates support for rte_power_monitor function */

Does AMD thing behave completely different from the x86?
Looking at patch 3, I understand this is not the case.

So we don't need a "amd" flag in the generic flags.
The indirection for calling the right ISA should be hidden in
rte_power_* helpers implemented for x86.


-- 
David Marchand