From: Mark Rutland <mark.rutland@arm.com>
To: Jisheng Zhang <jszhang@kernel.org>
Cc: Thomas Gleixner <tglx@kernel.org>,
ardb@kernel.org, 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 13:11:46 +0000 [thread overview]
Message-ID: <aZxSEoFkXMg18qLV@J2N7QTR9R3> (raw)
In-Reply-To: <aZxLE-wNGaEGDHGI@xhacker>
On Mon, Feb 23, 2026 at 08:41:55PM +0800, Jisheng Zhang wrote:
> 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.
There are various reasons for not supporting static calls, and in
general we end up having to have a fall-back path that's *more*
expensive than just loading the pointer.
> 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],
To be clear, that's ONE specific concern, not the ONLY reason.
> 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.
As per my other mail, does this meaningfully affect a real workload?
> Another alternative: disable static call if CFI is enabled, and give
> the platform/SoC users chance to enable static call to benefit from
> it.
Who is this actually going to matter to?
Mark.
>
> 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
>
next prev parent reply other threads:[~2026-02-23 13:11 UTC|newest]
Thread overview: 21+ 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 ` [PATCH 1/3] vmlinux.lds.h: add _handle_arch_irq RUNTIME_CONST section Jisheng Zhang
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
2026-02-22 22:06 ` Thomas Gleixner
2026-02-23 12:41 ` Jisheng Zhang
2026-02-23 13:11 ` Mark Rutland [this message]
2026-02-23 13:22 ` Jisheng Zhang
2026-02-23 13:55 ` Mark Rutland
2026-02-24 1:40 ` Guo Ren
2026-02-24 1:59 ` Guo Ren
2026-02-20 9:09 ` [PATCH 3/3] arm64: " Jisheng Zhang
2026-02-20 12:34 ` Leo Yan
2026-02-20 13:16 ` Jisheng Zhang
2026-02-20 13:34 ` Jisheng Zhang
2026-02-20 16:47 ` Leo Yan
2026-02-21 0:14 ` Jisheng Zhang
2026-02-23 9:15 ` Leo Yan
2026-02-25 14:40 ` Jisheng Zhang
2026-02-23 12:56 ` Mark Rutland
2026-02-23 12:58 ` Jisheng Zhang
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