linux-kernel - RE: [PATCH] clocksource/drivers/hyper-v: Include asm/hyperv-tlfs.h not asm/mshyperv.h

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Message-ID: <87iljituvh.ffs@tglx>
Date:   Sun, 13 Nov 2022 22:19:46 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Andy Lutomirski <luto@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: RE: [PATCH] clocksource/drivers/hyper-v: Include asm/hyperv-tlfs.h
 not asm/mshyperv.h

On Sun, Nov 13 2022 at 13:12, Michael Kelley wrote:
> From: Thomas Gleixner <tglx@...utronix.de> Sent: Sunday, November 13, 2022 1:50 AM
>> On Sat, Nov 12 2022 at 21:55, Michael Kelley wrote:
>> > But I can see the problem with too much getting dragged into the VDSO
>> > builds.  If hv_get_raw_timer() is added to hyperv_timer.h, it should
>> > be under #ifdef CONFIG_X86.  Adding an #ifdef isn't ideal, and a more
>> > more proper solution might be to have a separate hyperv_timer.h include
>> > file under arch/x86/include/asm.  But the latter seems like overkill for just
>> > hv_get_raw_timer(), so I'm OK with the #ifdef.
>> 
>> We surely can have asm/hyperv_timer.h but TBH:
>> 
>> >>  static inline notrace u64
>> >>  hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 *cur_tsc)
>> >>  {
>> 
>> hv_read_tsc_page_tsc() does not look architecture agnostic either. TSC
>> is pretty x86 specific :)
>
> Yes, the naming still says "tsc".  But there's nothing in the code that actually
> requires the TSC if hv_get_raw_timer() maps to some other hardware counter on
> a different architecture.   That's why the hv_get_raw_timer() abstraction is there
> in the first place.  If we didn't care about x86-isms, hv_read_tsc_page_tsc() would
> just directly invoke rdtsc_ordered().

Not really intuitive, but anyway...