IOMMU option in bios
Charles Kroeger
save 64MB of RAM if I enabled the IOMMU option in the bios.
I'm using an ASUS M4A79XTD EVO board with 8GB of RAM so maybe freeing up
64MB of RAM isn't that big of a deal; however, I had a look in the bios setup
and saw nothing that pertained to IOMMU to enable.
The BIOS is an 8MB Flash ROM, AMI BIOS PnP etc.
Can anyone eleborate on this message in dmesg?
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Johan Grönqvist
> I was looking over a dmesg output and I noticed a message that said I would
> save 64MB of RAM if I enabled the IOMMU option in the bios.
>
>
>
A post that tries to elaborate is at
<http://bogdan.org.ua/2009/09/30/iommu-this-costs-you-64-mb-of-ram.html>.
I had other symptoms as well, and used iommu=soft as boot option for a
while, but if you do not see any other problems relating to iommu, I
would ignore it.
/ johan
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Charles Kroeger
save 64MB of RAM if I enabled the IOMMU option in the bios.
I'm using an ASUS M4A79XTD EVO board with 8GB of RAM so maybe freeing up
64MB of RAM isn't that big of a deal; however, I had a look in the bios setup
and saw nothing that pertained to IOMMU to enable.
The BIOS is an 8MB Flash ROM, AMI BIOS PnP etc.
Can anyone eleborate on this message in dmesg?
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C
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Camaleón
> I was looking over a dmesg output and I noticed a message that said I
> would save 64MB of RAM if I enabled the IOMMU option in the bios.
>
> I'm using an ASUS M4A79XTD EVO board with 8GB of RAM so maybe freeing up
> 64MB of RAM isn't that big of a deal; however, I had a look in the bios
> setup and saw nothing that pertained to IOMMU to enable.
>
> The BIOS is an 8MB Flash ROM, AMI BIOS PnP etc.
>
> Can anyone eleborate on this message in dmesg?
Not sure if this has something to do with some BIOS option that allow
"memmory remapping" :-?
There is an Ubuntu forum thread that may help a bit:
***
"Your BIOS doesn't leave a aperture memory hole" / "This costs you 64 MB
of RAM"
http://ubuntuforums.org/showthread.php?t=1018854&highlight=enable+iommu+option+bios
***
Greetings,
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Clive McBarton
Hash: SHA1
Camaleón wrote:
> Not sure if this has something to do with some BIOS option that allow
> "memmory remapping" :-?
There's no such option. Not in any BIOS I've ever seen.
> There is an Ubuntu forum thread that may help a bit
It doesn't. It's a long thread with people talking about the problem,
suggesting a great number of "solutions" (some of them harmful) without
solving the problem.
On the other hand, nothing else I've seen so far solves the problem
either. Most people ignore it, since it may be just an annoying message,
the loss of a tiny fraction of RAM, and possibly your RAM becoming
slightly slower.
Are there any users of 64bit Debian with 4GB or more who are not affected?
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Camaleón
> Camaleón wrote:
>> Not sure if this has something to do with some BIOS option that allow
>> "memmory remapping" :-?
>
> There's no such option. Not in any BIOS I've ever seen.
That could be the problem.
>> There is an Ubuntu forum thread that may help a bit
>
> It doesn't. It's a long thread with people talking about the problem,
> suggesting a great number of "solutions" (some of them harmful) without
> solving the problem.
Didn' you try some of the tips? They only require passing some options to
the kernel at boot time and there is nothing harmful in doing that :-?
> On the other hand, nothing else I've seen so far solves the problem
> either. Most people ignore it, since it may be just an annoying message,
> the loss of a tiny fraction of RAM, and possibly your RAM becoming
> slightly slower.
I passed the link not because it provided a "magic solution" but for you
get an idea of the origin of that message and how to bypass it ;-)
> Are there any users of 64bit Debian with 4GB or more who are not
> affected?
Sure.
I am not getting that message in dmesg (running lenny amd64, 8 GiB.)
*but* my BIOS has "memory reclaiming" enabled.
Greetings,
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Clive McBarton
Hash: SHA1
Camaleón wrote:
> Didn' you try some of the tips? They only require passing some options to
> the kernel at boot time and there is nothing harmful in doing that :-?
Most of them are harmless. Some even make the error message go away. At
least one of the suggestions (passing the option iommu=false) ist
harmful though (disables USB).
> I passed the link not because it provided a "magic solution" but for you
> get an idea of the origin of that message and how to bypass it ;-)
Yes, I agree.
> I am not getting that message in dmesg (running lenny amd64, 8 GiB.)
> *but* my BIOS has "memory reclaiming" enabled.
Interesting. Intel CPU? Because in the forum whose link you posted, all
the CPUs in people's signatures were (as far as I see) made by AMD.
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Camaleón
> Camaleón wrote:
>> Didn' you try some of the tips? They only require passing some options
>> to the kernel at boot time and there is nothing harmful in doing that
>> :-?
>
> Most of them are harmless. Some even make the error message go away. At
> least one of the suggestions (passing the option iommu=false) ist
> harmful though (disables USB).
O.K., but disabling USB is not going to make any permament damage to your
system. Next boot your computer will be USB-aware again, so nothing you
should worry about.
>> I passed the link not because it provided a "magic solution" but for
>> you get an idea of the origin of that message and how to bypass it ;-)
>
> Yes, I agree.
>
>> I am not getting that message in dmesg (running lenny amd64, 8 GiB.)
>> *but* my BIOS has "memory reclaiming" enabled.
>
> Interesting. Intel CPU? Because in the forum whose link you posted, all
> the CPUs in people's signatures were (as far as I see) made by AMD.
Yep, Intel micro/chipset.
Maybe this message is AMD-centric? In fact, all messages in forum's
thread, as you noticed, are pointing to AMD micros. Someone here using
"AMD processor/64 bits Debian/8 GiB ram" could check for this message and
make any comment :-)
Greetings,
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Camaleón
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