linux-kernel - Re: [PATCH RFC 09/13] x86/irq: Install posted MSI notification handler

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Date:   Wed, 15 Nov 2023 12:05:06 -0800
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 Kernel <x86@...nel.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>,
        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 RFC 09/13] x86/irq: Install posted MSI notification
 handler

Hi Peter,

On Wed, 15 Nov 2023 13:42:21 +0100, Peter Zijlstra <peterz@...radead.org>
wrote:

> On Sat, Nov 11, 2023 at 08:16:39PM -0800, Jacob Pan wrote:
> 
> > +static __always_inline inline void handle_pending_pir(struct pi_desc
> > *pid, struct pt_regs *regs) +{
> > +	int i, vec = FIRST_EXTERNAL_VECTOR;
> > +	u64 pir_copy[4];
> > +
> > +	/*
> > +	 * Make a copy of PIR which contains IRQ pending bits for
> > vectors,
> > +	 * then invoke IRQ handlers for each pending vector.
> > +	 * If any new interrupts were posted while we are processing,
> > will
> > +	 * do again before allowing new notifications. The idea is to
> > +	 * minimize the number of the expensive notifications if IRQs
> > come
> > +	 * in a high frequency burst.
> > +	 */
> > +	for (i = 0; i < 4; i++)
> > +		pir_copy[i] = raw_atomic64_xchg((atomic64_t
> > *)&pid->pir_l[i], 0);  
> 
> Might as well use arch_xchg() and save the atomic64_t casting.
will do

> 
>  [...]  


Thanks,

Jacob