linux-kernel - Re: [PATCH] Cleanup __pvclock_read_cycles to remove useless variables

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Message-ID: <CALCETrVwn_bqeuuv7UbZzr8T2M+krjaDNgrqWd3vX0gujPm5sA@mail.gmail.com>
Date:	Sat, 30 Apr 2016 14:57:59 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...e.de>
Cc:	Paolo Bonzini <pbonzini@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
	Minfei Huang <mnghuan@...il.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] Cleanup __pvclock_read_cycles to remove useless variables

On Apr 30, 2016 12:17 PM, "Borislav Petkov" <bp@...e.de> wrote:
>
> On Sat, Apr 30, 2016 at 10:47:49AM -0700, Andy Lutomirski wrote:
> > Take a look at vread_pvclock.  I decided that __pvclock_read_cycles
> > was too ugly to use and was very slow and I just gave up and rewrote
> > it.
>
> Should we kill __pvclock_read_cycles in favor of vread_pvclock? It looks
> doable at a quick scan...
>

The in-kernel version might have to be a bit different because it
needs to handle the !stable case.  If !stable, it should just use the
current CPU's copy which means that, realistically, it should just
get_cpu and use the local copy unconditionally.  Other than that, it
could look a lot like the vread_pvclock variant.

But I agree, the current thing is incomprehensible.

--Andy

> --
> Regards/Gruss,
>     Boris.
>
> SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
> --