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From: David Gibson <david@gibson.dropbear.id.au>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: fam@euphon.net, mst@redhat.com, mark.cave-ayland@ilande.co.uk,
	qemu-devel@nongnu.org, kraxel@redhat.com, den@openvz.org,
	qemu-block@nongnu.org, quintela@redhat.com, armbru@redhat.com,
	pasic@linux.ibm.com, borntraeger@de.ibm.com,
	marcandre.lureau@redhat.com, ehabkost@redhat.com, sw@weilnetz.de,
	dgilbert@redhat.com, yuval.shaia@oracle.com,
	alex.williamson@redhat.com, stefanha@redhat.com,
	pbonzini@redhat.com, kwolf@redhat.com, cohuck@redhat.com,
	qemu-s390x@nongnu.org, mreitz@redhat.com, qemu-ppc@nongnu.org,
	Wei Yang <richardw.yang@linux.intel.com>,
	imammedo@redhat.com
Subject: Re: [PATCH 1/2] cpu: use ROUND_UP() to define xxx_PAGE_ALIGN
Date: Mon, 14 Oct 2019 10:36:22 +1100
Message-ID: <20191013233622.GK4080@umbus.fritz.box> (raw)
In-Reply-To: <41a924dc-f91b-c03b-4f82-570757105798@linaro.org>

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On Sun, Oct 13, 2019 at 11:56:35AM -0400, Richard Henderson wrote:
> On 10/12/19 10:11 PM, Wei Yang wrote:
> > Use ROUND_UP() to define, which is a little bit easy to read.
> > 
> > Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> > ---
> >  include/exec/cpu-all.h | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
> > index ad9ab85eb3..255bb186ac 100644
> > --- a/include/exec/cpu-all.h
> > +++ b/include/exec/cpu-all.h
> > @@ -220,7 +220,7 @@ extern int target_page_bits;
> >  
> >  #define TARGET_PAGE_SIZE (1 << TARGET_PAGE_BITS)
> >  #define TARGET_PAGE_MASK ~(TARGET_PAGE_SIZE - 1)
> > -#define TARGET_PAGE_ALIGN(addr) (((addr) + TARGET_PAGE_SIZE - 1) & TARGET_PAGE_MASK)
> > +#define TARGET_PAGE_ALIGN(addr) ROUND_UP((addr), TARGET_PAGE_SIZE)
> >  
> >  /* Using intptr_t ensures that qemu_*_page_mask is sign-extended even
> >   * when intptr_t is 32-bit and we are aligning a long long.
> > @@ -228,9 +228,8 @@ extern int target_page_bits;
> >  extern uintptr_t qemu_host_page_size;
> >  extern intptr_t qemu_host_page_mask;
> >  
> > -#define HOST_PAGE_ALIGN(addr) (((addr) + qemu_host_page_size - 1) & qemu_host_page_mask)
> > -#define REAL_HOST_PAGE_ALIGN(addr) (((addr) + qemu_real_host_page_size - 1) & \
> > -                                    qemu_real_host_page_mask)
> > +#define HOST_PAGE_ALIGN(addr) ROUND_UP((addr), qemu_host_page_size)
> > +#define REAL_HOST_PAGE_ALIGN(addr) ROUND_UP((addr), qemu_real_host_page_size)
> 
> 
> No, please.
> 
> (1) The compiler does not know that qemu_*host_page_size is a power of 2, and
> will generate a real division at runtime.  The same is true for
> TARGET_PAGE_SIZE when TARGET_PAGE_BITS_VARY.

Ouch, good point, I didn't think of that when I gave an R-b.

> (2) The first hunk conflicts with an in-flight patch of mine:
> 
> https://lists.gnu.org/archive/html/qemu-devel/2019-09/msg04526.html
> 
> 
> r~
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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  reply index

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-13  2:11 [PATCH 0/2] cleanup on page size Wei Yang
2019-10-13  2:11 ` [PATCH 1/2] cpu: use ROUND_UP() to define xxx_PAGE_ALIGN Wei Yang
2019-10-13  6:34   ` Michael S. Tsirkin
2019-10-13  9:27   ` David Gibson
2019-10-13 15:56   ` Richard Henderson
2019-10-13 23:36     ` David Gibson [this message]
2019-10-14  1:01     ` Wei Yang
2019-10-14  2:38       ` Richard Henderson
2019-10-14  3:19         ` Wei Yang
2019-10-14 16:25   ` Juan Quintela
2019-10-13  2:11 ` [PATCH 2/2] core: replace getpagesize() with qemu_real_host_page_size Wei Yang
2019-10-13  6:35   ` Michael S. Tsirkin
2019-10-13  9:28   ` David Gibson
2019-10-16  1:25     ` Wei Yang
2019-10-13 16:03   ` Richard Henderson
2019-10-14  9:15   ` Dr. David Alan Gilbert
2019-10-14 21:36     ` Wei Yang
2019-10-14 23:12       ` Richard Henderson
2019-10-15 11:45   ` Yuval Shaia
2019-10-16  1:07     ` Wei Yang
2019-10-23  9:19   ` Paolo Bonzini
2019-10-13  6:36 ` [PATCH 0/2] cleanup on page size Michael S. Tsirkin
2019-10-14 21:59 ` Wei Yang

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