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

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Date:	Wed, 11 May 2016 23:19:57 +0800
From:	Minfei Huang <mnghuan@...il.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
	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 05/11/16 at 04:24P, Paolo Bonzini wrote:
> 
> 
> On 30/04/2016 23:57, Andy Lutomirski wrote:
> >> > 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.
> 
> It also lacks smp_rmb()s.  One is more or less implicit in rdtsc, but
> you need one to separate __pvclock_read_cycles's reads of src->foo from
> pvclock_read_flags's read of src->version.
> 
> Minfei, would you like to take a look?

Sure. I will take a look about this issue.

Thanks
Minfei

> 
> Paolo