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From: Jisheng Zhang <jszhang@kernel.org>
To: Thomas Gleixner <tglx@kernel.org>, ardb@kernel.org, mark.rutland@arm.com
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>, Guo Ren <guoren@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-riscv@lists.infradead.org, linux-csky@vger.kernel.org
Subject: Re: [PATCH 2/3] genirq: use runtime constant to optimize handle_arch_irq access
Date: Mon, 23 Feb 2026 20:41:55 +0800	[thread overview]
Message-ID: <aZxLE-wNGaEGDHGI@xhacker> (raw)
In-Reply-To: <877bs4wi0c.ffs@tglx>

On Sun, Feb 22, 2026 at 11:06:11PM +0100, Thomas Gleixner wrote:
> On Fri, Feb 20 2026 at 17:09, Jisheng Zhang wrote:
> > Currently, on GENERIC_IRQ_MULTI_HANDLER platforms, the handle_arch_irq
> > is a pointer which is set during booting, and every irq processing needs
> > to access it, so it sits in hot code path. We can use the
> > runtime constant mechanism which was introduced by Linus to speed up
> > its accessing.
> 
> The proper solution is to use a static call and update it in
> set_handle_irq().  That removes the complete indirect call issue from
> the hot path.

+ Ard, Mark,

Good idea. The remaining problem is no static call support for current
GENERIC_IRQ_MULTI_HANDLER (or similar, arm64 e.g) platforms.

For arm64, Ard tried to add the static call support[1] in 2021, but
Mark concerned "compiler could easily violate our expectations in
future"[2], and asked for static calls "critical rather than a
nice-to-have" usage.

Hi Ard, Mark,

Could this irq performance improvement be used as a "critical" usage for
arm64 static call? Per my test, about 6.5% improvement was seen on quad CA55.

Another alternative: 
disable static call if CFI is enabled, and give the platform/SoC users
chance to enable static call to benefit from it.

Any comment is appreciated.

Thanks


[1] https://www.spinics.net/lists/arm-kernel/msg931861.html

[2] https://www.spinics.net/lists/arm-kernel/msg932481.html

> 
> Thanks,
> 
>         tglx

WARNING: multiple messages have this Message-ID (diff)
From: Jisheng Zhang <jszhang@kernel.org>
To: Thomas Gleixner <tglx@kernel.org>, ardb@kernel.org, mark.rutland@arm.com
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>, Guo Ren <guoren@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-riscv@lists.infradead.org, linux-csky@vger.kernel.org
Subject: Re: [PATCH 2/3] genirq: use runtime constant to optimize handle_arch_irq access
Date: Mon, 23 Feb 2026 20:41:55 +0800	[thread overview]
Message-ID: <aZxLE-wNGaEGDHGI@xhacker> (raw)
In-Reply-To: <877bs4wi0c.ffs@tglx>

On Sun, Feb 22, 2026 at 11:06:11PM +0100, Thomas Gleixner wrote:
> On Fri, Feb 20 2026 at 17:09, Jisheng Zhang wrote:
> > Currently, on GENERIC_IRQ_MULTI_HANDLER platforms, the handle_arch_irq
> > is a pointer which is set during booting, and every irq processing needs
> > to access it, so it sits in hot code path. We can use the
> > runtime constant mechanism which was introduced by Linus to speed up
> > its accessing.
> 
> The proper solution is to use a static call and update it in
> set_handle_irq().  That removes the complete indirect call issue from
> the hot path.

+ Ard, Mark,

Good idea. The remaining problem is no static call support for current
GENERIC_IRQ_MULTI_HANDLER (or similar, arm64 e.g) platforms.

For arm64, Ard tried to add the static call support[1] in 2021, but
Mark concerned "compiler could easily violate our expectations in
future"[2], and asked for static calls "critical rather than a
nice-to-have" usage.

Hi Ard, Mark,

Could this irq performance improvement be used as a "critical" usage for
arm64 static call? Per my test, about 6.5% improvement was seen on quad CA55.

Another alternative: 
disable static call if CFI is enabled, and give the platform/SoC users
chance to enable static call to benefit from it.

Any comment is appreciated.

Thanks


[1] https://www.spinics.net/lists/arm-kernel/msg931861.html

[2] https://www.spinics.net/lists/arm-kernel/msg932481.html

> 
> Thanks,
> 
>         tglx

_______________________________________________
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linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

  reply	other threads:[~2026-02-23 13:00 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-02-20  9:09 [PATCH 0/3] use runtime constant to optimize handle_arch_irq access Jisheng Zhang
2026-02-20  9:09 ` Jisheng Zhang
2026-02-20  9:09 ` [PATCH 1/3] vmlinux.lds.h: add _handle_arch_irq RUNTIME_CONST section Jisheng Zhang
2026-02-20  9:09   ` Jisheng Zhang
2026-02-24  2:01   ` Guo Ren
2026-02-24  2:01     ` Guo Ren
2026-02-20  9:09 ` [PATCH 2/3] genirq: use runtime constant to optimize handle_arch_irq access Jisheng Zhang
2026-02-20  9:09   ` Jisheng Zhang
2026-02-22 22:06   ` Thomas Gleixner
2026-02-22 22:06     ` Thomas Gleixner
2026-02-23 12:41     ` Jisheng Zhang [this message]
2026-02-23 12:41       ` Jisheng Zhang
2026-02-23 13:11       ` Mark Rutland
2026-02-23 13:11         ` Mark Rutland
2026-02-23 13:22         ` Jisheng Zhang
2026-02-23 13:22           ` Jisheng Zhang
2026-02-23 13:55           ` Mark Rutland
2026-02-23 13:55             ` Mark Rutland
2026-02-24  1:40   ` Guo Ren
2026-02-24  1:40     ` Guo Ren
2026-02-24  1:59     ` Guo Ren
2026-02-24  1:59       ` Guo Ren
2026-02-20  9:09 ` [PATCH 3/3] arm64: " Jisheng Zhang
2026-02-20  9:09   ` Jisheng Zhang
2026-02-20 12:34   ` Leo Yan
2026-02-20 12:34     ` Leo Yan
2026-02-20 13:16     ` Jisheng Zhang
2026-02-20 13:16       ` Jisheng Zhang
2026-02-20 13:34       ` Jisheng Zhang
2026-02-20 13:34         ` Jisheng Zhang
2026-02-20 16:47         ` Leo Yan
2026-02-20 16:47           ` Leo Yan
2026-02-21  0:14           ` Jisheng Zhang
2026-02-21  0:14             ` Jisheng Zhang
2026-02-23  9:15             ` Leo Yan
2026-02-23  9:15               ` Leo Yan
2026-02-25 14:40               ` Jisheng Zhang
2026-02-25 14:40                 ` Jisheng Zhang
2026-02-23 12:56   ` Mark Rutland
2026-02-23 12:56     ` Mark Rutland
2026-02-23 12:58     ` Jisheng Zhang
2026-02-23 12:58       ` Jisheng Zhang

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