linux-kernel - Re: [PATCH V2 00/19] timekeeping: Handle potential multiplication overflow

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Date: Mon, 25 Mar 2024 19:11:21 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Adrian Hunter" <adrian.hunter@...el.com>,
 "Thomas Gleixner" <tglx@...utronix.de>
Cc: "Peter Zijlstra" <peterz@...radead.org>,
 "Dave Hansen" <dave.hansen@...ux.intel.com>,
 "John Stultz" <jstultz@...gle.com>, "H. Peter Anvin" <hpa@...or.com>,
 "Alexander Gordeev" <agordeev@...ux.ibm.com>,
 "Vincenzo Frascino" <vincenzo.frascino@....com>, linux-s390@...r.kernel.org,
 x86@...nel.org, "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
 "Ingo Molnar" <mingo@...hat.com>,
 "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
 "Christian Borntraeger" <borntraeger@...ux.ibm.com>,
 "Vasily Gorbik" <gor@...ux.ibm.com>, "Heiko Carstens" <hca@...ux.ibm.com>,
 "Nicholas Piggin" <npiggin@...il.com>, "Borislav Petkov" <bp@...en8.de>,
 "Andy Lutomirski" <luto@...nel.org>, "Bjorn Helgaas" <bhelgaas@...gle.com>,
 "Anna-Maria Gleixner" <anna-maria@...utronix.de>,
 "Stephen Boyd" <sboyd@...nel.org>, "Randy Dunlap" <rdunlap@...radead.org>,
 linux-kernel@...r.kernel.org, "Sven Schnelle" <svens@...ux.ibm.com>,
 linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH V2 00/19] timekeeping: Handle potential multiplication overflow

On Mon, Mar 25, 2024, at 07:40, Adrian Hunter wrote:
>
> Extend the facility also to VDSO, dependent on new config option
> GENERIC_VDSO_OVERFLOW_PROTECT which is selected by x86 only, so other
> architectures are not affected. The result is a calculation that has
> similar performance as before. Most machines showed performance benefit,
> except Skylake-based hardware such as Intel Kaby Lake which was seen <1%
> worse.

I've read through the series, and this pretty much all makes sense,
nice work!

There are a few patches that just rearrange the local variable
declarations to save a few lines, and I don't see those as an
improvement, but they also don't hurt aside from distracting
slightly from the real changes.

     Arnd