linux-kernel - Re: [PATCH] x86: branchless clear

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Message-ID: <20160823161502.GA1842@p183.telecom.by>
Date:   Tue, 23 Aug 2016 19:15:03 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Brian Gerst <brgerst@...il.com>
Cc:     the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: branchless clear_page()

On Tue, Aug 23, 2016 at 09:43:25AM -0400, Brian Gerst wrote:
> > -ENTRY(clear_page_c_e)
> > +ENTRY(clear_page_rep_stosb)
> >         movl $4096,%ecx
> >         xorl %eax,%eax
> >         rep stosb
> >         ret
> > -ENDPROC(clear_page_c_e)
> > +ENDPROC(clear_page_rep_stosb)
> 
> I like this idea, but does it make sense to take it a step further and
> inline the string instruction alternatives to avoid a call altogether?

It is easy but you can't do runtime patching then.

> Also, 32-bit should be converted to do the same thing as 64-bit.

I don't run 32-bit. :-)