linux-kernel - Re: [PATCH 04/15] x86/irq: Add a Kconfig option for posted MSI

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Date: Fri, 5 Apr 2024 08:54:46 -0700
From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
To: Robert Hoo <robert.hoo.linux@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>, X86 Kernel <x86@...nel.org>, Peter
 Zijlstra <peterz@...radead.org>, iommu@...ts.linux.dev, Thomas Gleixner
 <tglx@...utronix.de>, Lu Baolu <baolu.lu@...ux.intel.com>,
 kvm@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>, Joerg Roedel
 <joro@...tes.org>, "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov
 <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>, Paul Luse
 <paul.e.luse@...el.com>, Dan Williams <dan.j.williams@...el.com>, Jens
 Axboe <axboe@...nel.dk>, Raj Ashok <ashok.raj@...el.com>, "Tian, Kevin"
 <kevin.tian@...el.com>, maz@...nel.org, seanjc@...gle.com, Robin Murphy
 <robin.murphy@....com>, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH 04/15] x86/irq: Add a Kconfig option for posted MSI

Hi Robert,

On Fri, 5 Apr 2024 10:28:59 +0800, Robert Hoo <robert.hoo.linux@...il.com>
wrote:

> On 1/27/2024 7:42 AM, Jacob Pan wrote:
> > This option will be used to support delivering MSIs as posted
> > interrupts. Interrupt remapping is required.
> > 
> > Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > ---
> >   arch/x86/Kconfig | 11 +++++++++++
> >   1 file changed, 11 insertions(+)
> > 
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 5edec175b9bf..79f04ee2b91c 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -463,6 +463,17 @@ config X86_X2APIC
> >   
> >   	  If you don't know what to do here, say N.
> >   
> > +config X86_POSTED_MSI
> > +	bool "Enable MSI and MSI-x delivery by posted interrupts"
> > +	depends on X86_X2APIC && X86_64 && IRQ_REMAP  
> 
> Does posted_msi really depend on x2APIC? PID.NDST encoding supports both
> xAPIC and x2APIC.
No, posted_msi works with xAPIC as well. I just fixed a bug in NDST xAPIC
encoding, will be in v2.

I was thinking from the performance advantage of x2APIC. But you are right
they are orthogonal.

> If posted_msi posts more stringent requirement, I think it deserves an 
> explanation in this patch's description.
> And, X86_X2APIC already depends on IRQ_REMAP, can we just list one of
> them here?
Will drop X2APIC dependency.

Thanks,

Jacob