linux-kernel - Re: [PATCH v3] x86/cpu: Use SERIALIZE in sync

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Message-ID: <20200806233906.GA27118@ranerica-svr.sc.intel.com>
Date:   Thu, 6 Aug 2020 16:39:06 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Tony Luck <tony.luck@...el.com>,
        Cathy Zhang <cathy.zhang@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Kyung Min Park <kyung.min.park@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-edac@...r.kernel.org
Subject: Re: [PATCH v3] x86/cpu: Use SERIALIZE in sync_core() when available

On Thu, Aug 06, 2020 at 04:08:47PM -0700, Dave Hansen wrote:
> On 8/6/20 4:04 PM, Ricardo Neri wrote:
> > 	 * CPUID is the conventional way, but it's nasty: it doesn't
> > 	 * exist on some 486-like CPUs, and it usually exits to a
> > 	 * hypervisor.
> > 	 *
> >  	 * The SERIALIZE instruction is the most straightforward way to
> >  	 * do this as it does not clobber registers or exit to a
> > 	 * hypervisor. However, it is not universally available.
> >  	 *
> > 	 * Like all of Linux's memory ordering operations, this is a
> > 	 * compiler barrier as well.
> > 	 */
> > 
> > What do you think?
> 
> I like what I suggested.  :)
> 
> SERIALIZE is best where available.  Do it first, comment it by itself.
> 
> Then, go into the long discussion of the other alternatives.  They only
> make sense when SERIALIZE isn't there, and the logic for selection there
> is substantially more complicated.

Sure Dave, I think this layout makes sense. I will rework the comments.

Thanks and BR,
Ricardo