linux-kernel - Re: [PATCH RFC 2/6] x86/hyper-v: add a function to read both TSC and TSC page value simulateneously

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Date:   Fri, 1 Dec 2017 18:52:48 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Stephen Hemminger <stephen@...workplumber.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Stephen Hemminger <sthemmin@...rosoft.com>, kvm@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, devel@...uxdriverproject.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH RFC 2/6] x86/hyper-v: add a function to read both TSC and
 TSC page value simulateneously

On 01/12/2017 18:29, Stephen Hemminger wrote:
>> +static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
>> +				       u64 *cur_tsc)
>> +{
>> +	*cur_tsc = rdtsc();
>> +
>> +	return cur_tsc;
> Why do return and setting by reference. Looks like an ugly API.

This is the fallback implementation for !CONFIG_HYPERV_TSCPAGE, which
explains why it's ugly, but why is it needed at all (or it could just
BUG())?

Thanks,

Paolo