linux-kernel - Re: [PATCH v2 0/3] arm64: perf_event: Fix time offset prior to epoch

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Message-ID: <20200512085741.GG2978@hirez.programming.kicks-ass.net>
Date:   Tue, 12 May 2020 10:57:41 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Allison Randal <allison@...utok.net>,
        Alexios Zavras <alexios.zavras@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Enrico Weigelt <info@...ux.net>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        Paul Cercueil <paul@...pouillou.net>,
        "Ben Dooks (Codethink)" <ben.dooks@...ethink.co.uk>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 0/3] arm64: perf_event: Fix time offset prior to epoch

On Tue, May 12, 2020 at 02:38:12PM +0800, Leo Yan wrote:

> I have verified this change, it works as expected on my Arm64 board.
> Also paste the updated code which makes building success with minor
> fixing.

W00t !

> I am not sure how to proceed, will you merge this?  Or you want me to
> send out formal patches (or only for the Arm64 part)?

I suppose I can write a Changelog for the thing, Will asked for another
change as well.

> P.s. it's shame I still missed you guys suggestion in prvious thread
> even though you have provide enough ifno, and thank you for the helping!

All good.


> ---8<---

> -	/*
> -	 * time_shift is not expected to be greater than 31 due to
> -	 * the original published conversion algorithm shifting a
> -	 * 32-bit value (now specifies a 64-bit value) - refer
> -	 * perf_event_mmap_page documentation in perf_event.h.
> -	 */
> -	if (shift == 32) {
> -		shift = 31;
> -		userpg->time_mult >>= 1;
> -	}

Is there a reason you completely lost that? IIRC I preserved that.
Although I don't know if it is still relevant.

I'll keep it for now, and removal can be a separate patch with proper
justification, ok?