linux-kernel - Re: [PATCH v2 08/10] clocksource/drivers/hyper-v: Handle sched

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Date:   Mon, 1 Mar 2021 15:25:26 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Michael Kelley <mikelley@...rosoft.com>, sthemmin@...rosoft.com,
        kys@...rosoft.com, wei.liu@...nel.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, arnd@...db.de,
        linux-hyperv@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH v2 08/10] clocksource/drivers/hyper-v: Handle sched_clock
 differences inline

On 01/03/2021 02:15, Michael Kelley wrote:
> While the Hyper-V Reference TSC code is architecture neutral, the
> pv_ops.time.sched_clock() function is implemented for x86/x64, but not
> for ARM64. Current code calls a utility function under arch/x86 (and
> coming, under arch/arm64) to handle the difference.
> 
> Change this approach to handle the difference inline based on whether
> GENERIC_SCHED_CLOCK is present.  The new approach removes code under
> arch/* since the difference is tied more to the specifics of the Linux
> implementation than to the architecture.
> 
> No functional change.
> 
> Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
> Reviewed-by: Boqun Feng <boqun.feng@...il.com>
> ---

[ ... ]

> +/*
> + * Reference to pv_ops must be inline so objtool
> + * detection of noinstr violations can work correctly.
> + */
> +static __always_inline void hv_setup_sched_clock(void *sched_clock)
> +{
> +#ifdef CONFIG_GENERIC_SCHED_CLOCK
> +	/*
> +	 * We're on an architecture with generic sched clock (not x86/x64).
> +	 * The Hyper-V sched clock read function returns nanoseconds, not
> +	 * the normal 100ns units of the Hyper-V synthetic clock.
> +	 */
> +	sched_clock_register(sched_clock, 64, NSEC_PER_SEC);
> +#else
> +#ifdef CONFIG_PARAVIRT
> +	/* We're on x86/x64 *and* using PV ops */
> +	pv_ops.time.sched_clock = sched_clock;
> +#endif
> +#endif
> +}
Please refer to:

Documentation/process/coding-style.rst

Section 21)

[ ... ]

Prefer to compile out entire functions, rather than portions of
functions or portions of expressions.

[ ... ]


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