linux-kernel - Re: [Xen-devel] [PATCH v3 19/20] xen/privcmd: Add support for Linux 64KB page granularity

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Message-ID: <alpine.DEB.2.02.1508101356200.11337@kaball.uk.xensource.com>
Date:	Mon, 10 Aug 2015 13:57:31 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Julien Grall <julien.grall@...rix.com>,
	<ian.campbell@...rix.com>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xenproject.org>,
	"Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Xen-devel] [PATCH v3 19/20] xen/privcmd: Add support for Linux
 64KB page granularity

On Mon, 10 Aug 2015, David Vrabel wrote:
> On 10/08/15 13:03, Stefano Stabellini wrote:
> > On Fri, 7 Aug 2015, Julien Grall wrote:
> >> -	rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap_range, &xatp);
> >> -	return rc < 0 ? rc : err;
> >> +	for (i = 0; i < nr_gfn; i++) {
> >> +		if ((i % XEN_PFN_PER_PAGE) == 0) {
> >> +			page = pages[i / XEN_PFN_PER_PAGE];
> > 
> > If this function is going to be called very frequently you might want to
> > consider using a shift instead.
> > 
> >     page = pages[i >> 4];
> > 
> > With an appropriate macro of course.
> 
> This change isn't necessary.  Compilers already turn divides into
> suitable shifts.

The ARM compiler I used last time I tested this did not, but that was 1
or 2 years ago. In any case to be clear this change is not required.
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