From: "John W. Linville" <linville@tuxdriver.com>
To: Stephen Williams <steve@icarus.com>
Cc: linuxppc-dev@ozlabs.org
Subject: Re: How to map memory uncached on PPC.
Date: Sat, 20 Aug 2005 14:08:28 -0400 [thread overview]
Message-ID: <20050820180825.GG2736@tuxdriver.com> (raw)
In-Reply-To: <4307536E.4070800@icarus.com>
On Sat, Aug 20, 2005 at 08:59:42AM -0700, Stephen Williams wrote:
> Benjamin Herrenschmidt wrote:
> >A simple experiment you can do is limit the memory used by the kernel
> >(booting with mem=xxxx) and then use mmap of /dev/mem to map the
> >remaining memory like if it was an IO device, uncached. With that, you
> >get a quick hack solution to validate the performance benefit at least.
>
> I did an even simpler experiment: I commented out the pci_map_single,
> which on a PPC only has the effect of calling invalidate_dcache_range
> and returning the virt_to_bus of the address. Obviously, the cache
> is still enabled for the processor, and the image data may get
> corrupted, but this was a performance test, not a solution.
If your purpose is to evaluate performance, doesn't having the cache
enabled limit the usefulness of your test? For example if your cache
uses a write-back policy then your test will probably outperform the
actual uncached accesses. YMMV, I suppose...
John
--
John W. Linville
linville@tuxdriver.com
next prev parent reply other threads:[~2005-08-20 18:12 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-08-19 15:17 How to map memory uncached on PPC Stephen Williams
2005-08-20 1:06 ` Benjamin Herrenschmidt
2005-08-20 15:59 ` Stephen Williams
2005-08-20 18:08 ` John W. Linville [this message]
2005-08-21 15:06 ` Stephen Williams
-- strict thread matches above, loose matches on Subject: below --
2005-08-19 16:18 Stephen Williams
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