Subject: Re: [PATCH RFC 2/6] x86/hyper-v: add a function to read both TSC and
 TSC page value simulateneously
To: Stephen Hemminger <stephen@networkplumber.org>,
        Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>, kvm@vger.kernel.org,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Haiyang Zhang <haiyangz@microsoft.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
        Andy Lutomirski <luto@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        devel@linuxdriverproject.org, Thomas Gleixner <tglx@linutronix.de>
References: <20171201131321.918-1-vkuznets@redhat.com>
 <20171201131321.918-3-vkuznets@redhat.com> <20171201092904.30d9831f@xeon-e3>
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <77674d0f-f4c6-ad47-1984-ea040e256501@redhat.com>
Date: Fri, 1 Dec 2017 18:52:48 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.4.0
MIME-Version: 1.0
In-Reply-To: <20171201092904.30d9831f@xeon-e3>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 447
Lines: 16

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