linux-kernel - Re: [PATCH v5 4/4] entry: Inline syscall_exit_to_user

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Message-ID: <Z8zb-L8bFMh_YHxO@ghost>
Date: Sat, 8 Mar 2025 16:08:24 -0800
From: Charlie Jenkins <charlie@...osinc.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Huacai Chen <chenhuacai@...nel.org>,
	WANG Xuerui <kernel@...0n.name>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	loongarch@...ts.linux.dev
Subject: Re: [PATCH v5 4/4] entry: Inline syscall_exit_to_user_mode()

On Sat, Mar 08, 2025 at 01:37:30PM +0100, Thomas Gleixner wrote:
> On Wed, Mar 05 2025 at 16:43, Charlie Jenkins wrote:
> > Architectures using the generic entry code can be optimized by having
> > syscall_exit_to_user_mode inlined.
> 
> That's a pretty handwavy claim. What's the actual benefit in numbers?

I put the numbers in the cover letter! Here is the data I gathered:

Testing was done with the byte-unixbench [1] syscall benchmark (which
calls getpid) and QEMU. On riscv I measured a 7.09246% improvement, on
x86 a 2.98843% improvement, on loongarch a 6.07954% improvement, and on
s390 a 11.1328% improvement.

The Intel bot also reported "kernel test robot noticed a 1.9%
improvement of stress-ng.seek.ops_per_sec" [2]

- Charlie

> 
> Thanks,
> 
>         tglx