linux-kernel - Re: [PATCH v2] vdso: Remove struct getcpu

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Message-ID: <cb5991f4-fc6b-43d9-a60b-f28b5eeda5d3@zytor.com>
Date: Mon, 13 Oct 2025 14:09:31 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...el.com>,
        Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
        Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Shuah Khan
 <shuah@...nel.org>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-um@...ts.infradead.org, linux-api@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2] vdso: Remove struct getcpu_cache

On 2025-10-13 13:32, Andy Lutomirski wrote:
> 
> The global timestamp would just be some field in the vvar area, which
> we have plenty of anyway.
> 
> But I agree, accelerating getcpu is pointless.  In any case, anything
> that historically thought it really really wanted accelerated getcpu
> can, and probably does, use rseq these days.
> 

Indeed. And with RDPID it is fast enough that the bulk of the cost is probably
in the vdso call.

	-hpa