Re: Architectures with strict alignment?
- From: Kostik Belousov <kostikbel@xxxxxxxxx>
- Date: Mon, 31 Dec 2007 13:33:27 +0200
On Mon, Dec 31, 2007 at 05:38:43PM +0800, Erich Dollansky wrote:
Hi,
Kostik Belousov wrote:
On Sat, Dec 29, 2007 at 01:12:04PM +0200, Kostik Belousov wrote:
On Sat, Dec 29, 2007 at 12:14:11AM -0800, Kip Macy wrote:
I.e., it seems that gcc does not feel too guilty generating unaligned
half-word writes on i386. :(
this should not be a problem inside a cache line.
If the access goes accross two cache lines and the other cache line is
not in the cache, it becomes real difficult.
I can't tell you what the hardware actually does in this case.
It should read the second affected cache line into the cache. But what
happens if the second affected cache line is blocked by another CPU
while the current CPU blocks the first cache line?
From the manual, 253668, 7.1.1:
Accesses to cacheable memory that are split across bus widths, cache
lines, and page boundaries are not guaranteed to be atomic by the Intel
Core 2 Duo, Intel Core Duo, Pentium M, Pentium 4, Intel Xeon, P6 family,
Pentium, and Intel486 processors. The Intel Core 2 Duo, Intel Core Duo,
Pentium M, Pentium 4, Intel Xeon, and P6 family processors provide bus
control signals that permit external memory subsystems to make split
accesses atomic; however, nonaligned data accesses will seriously impact
the performance of the processor and should be avoided.
I think we might get any half of the operation as a result.
Attachment:
pgpWM0fJD5wtO.pgp
Description: PGP signature
- Follow-Ups:
- Re: Architectures with strict alignment?
- From: Erich Dollansky
- Re: Architectures with strict alignment?
- References:
- Architectures with strict alignment?
- From: Ivan Voras
- Re: Architectures with strict alignment?
- From: Erich Dollansky
- Re: Architectures with strict alignment?
- From: Kip Macy
- Re: Architectures with strict alignment?
- From: Kostik Belousov
- Re: Architectures with strict alignment?
- From: Kostik Belousov
- Re: Architectures with strict alignment?
- From: Erich Dollansky
- Architectures with strict alignment?
- Prev by Date: Re: Architectures with strict alignment?
- Next by Date: Re: BSD license compatible hash algorithm?
- Previous by thread: Re: Architectures with strict alignment?
- Next by thread: Re: Architectures with strict alignment?
- Index(es):
Relevant Pages
|
