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Message-ID: <87wmcn4x78.ffs@tglx>
Date: Mon, 17 Mar 2025 14:13:15 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Sean Christopherson <seanjc@...gle.com>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
x86@...nel.org, Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
<pbonzini@...hat.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, Jacob Pan
<jacob.jun.pan@...ux.intel.com>, Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH 2/8] x86/irq: Track if IRQ was found in PIR during
initial loop (to load PIR vals)
On Fri, Mar 14 2025 at 20:06, Sean Christopherson wrote:
> @@ -409,25 +409,28 @@ static __always_inline bool handle_pending_pir(u64 *pir, struct pt_regs *regs)
> {
> int i, vec = FIRST_EXTERNAL_VECTOR;
> unsigned long pir_copy[4];
> - bool handled = false;
> + bool found_irq = false;
>
> - for (i = 0; i < 4; i++)
> + for (i = 0; i < 4; i++) {
> pir_copy[i] = READ_ONCE(pir[i]);
> + if (pir_copy[i])
> + found_irq = true;
> + }
That's four extra conditional branches. You can avoid them completely. See
delta patch below.
Thanks,
tglx
---
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -407,17 +407,15 @@ void intel_posted_msi_init(void)
*/
static __always_inline bool handle_pending_pir(u64 *pir, struct pt_regs *regs)
{
+ unsigned long pir_copy[4], pend = 0;
int i, vec = FIRST_EXTERNAL_VECTOR;
- unsigned long pir_copy[4];
- bool found_irq = false;
for (i = 0; i < 4; i++) {
pir_copy[i] = READ_ONCE(pir[i]);
- if (pir_copy[i])
- found_irq = true;
+ pend |= pir_copy[i];
}
- if (!found_irq)
+ if (!pend)
return false;
for (i = 0; i < 4; i++) {
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