linux-kernel - Re: [PATCH 3/3] x86/vmware: Add paravirt sched clock

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Message-ID: <alpine.DEB.2.20.1610261213000.4983@nanos>
Date:   Wed, 26 Oct 2016 12:18:33 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Alexey Makhalov <amakhalov@...are.com>
cc:     corbet@....net, akataria@...are.com, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, monitor-list@...are.com,
        pv-drivers@...are.com, time-lords@...are.com
Subject: Re: [PATCH 3/3] x86/vmware: Add paravirt sched clock

On Tue, 25 Oct 2016, Alexey Makhalov wrote:
> no-vmw-sched-clock kernel parameter is added to switch back to the
> native_sched_clock() implementation.

You are not switching back. The parameter is used to disable the paravirt
sched clock.

>  #ifdef CONFIG_PARAVIRT
> +static struct cyc2ns_data vmware_cyc2ns __ro_after_init;
> +
> +static int vmw_sched_clock __initdata = 1;
> +static __init int setup_vmw_sched_clock(char *s)

Please stop glueing a variable to a function w/o a new line between
them. It's just stopping the reading flow.

> +{
> +	vmw_sched_clock = 0;
> +	return 0;
> +}
> +early_param("no-vmw-sched-clock", setup_vmw_sched_clock);
> +
> +static unsigned long long vmware_sched_clock(void)
> +{
> +	unsigned long long ns;
> +
> +	ns = mul_u64_u32_shr(rdtsc(), vmware_cyc2ns.cyc2ns_mul,
> +			     vmware_cyc2ns.cyc2ns_shift);
> +	ns -= vmware_cyc2ns.cyc2ns_offset;
> +	return ns;
> +}
> +
>  static void __init vmware_paravirt_ops_setup(void)
>  {
>  	pv_info.name = "VMware";
>  	pv_cpu_ops.io_delay = paravirt_nop;
> +
> +	if (vmware_tsc_khz && vmw_sched_clock) {
> +		unsigned long long tsc_now = rdtsc();
> +
> +		clocks_calc_mult_shift(&vmware_cyc2ns.cyc2ns_mul,
> +				       &vmware_cyc2ns.cyc2ns_shift,
> +				       vmware_tsc_khz,
> +				       NSEC_PER_MSEC, 0);
> +		vmware_cyc2ns.cyc2ns_offset =
> +			mul_u64_u32_shr(tsc_now, vmware_cyc2ns.cyc2ns_mul,
> +					vmware_cyc2ns.cyc2ns_shift);
> +
> +		pv_time_ops.sched_clock = vmware_sched_clock;
> +		pr_info("vmware: using sched offset of %llu ns\n",

Please use pr_fmt instead of adding the prefix to every print.

Thanks,

	tglx