From: David Daney <ddaney.cavm@gmail.com>
To: Ronny Meeus <ronny.meeus@gmail.com>
Cc: "Maciej W. Rozycki" <macro@linux-mips.org>,
Rich Felker <dalias@aerifal.cx>,
linux-mips@linux-mips.org, "Pinski,
Andrew" <Andrew.Pinski@caviumnetworks.com>
Subject: Re: 2GB userspace limitation in ABI N32
Date: Wed, 10 Oct 2012 11:08:49 -0700 [thread overview]
Message-ID: <5075B9B1.2050503@gmail.com> (raw)
In-Reply-To: <CAMJ=MEf2LFcWLo8f061-WiM9dMt-hQJUmoRCCs6agZvc2VQrNQ@mail.gmail.com>
On 10/10/2012 10:49 AM, Ronny Meeus wrote:
> This is exactly the platform we are targeting:
> - a Cavium processor
> - running 64bit Linux
> - 4Gb of ram of which almost 3Gb will be used by 1 process (consisting
> of multiple threads)
>
> It would be really great that we could get help from you guys here.
As far as I know, we are not actively working on this. So, as I see it,
your options are:
A) Use n64.
B) Do all the work yourself.
C) Pay someone to do the work for you.
David Daney
> Many thanks for the effort you are putting into this.
>
> On Wed, Oct 10, 2012 at 7:34 PM, David Daney <ddaney.cavm@gmail.com> wrote:
>> On 10/10/2012 10:10 AM, Maciej W. Rozycki wrote:
>>>
>>> On Wed, 10 Oct 2012, David Daney wrote:
>>>
>>>> The only disadvantage of doing this is that the code will be slightly
>>>> larger/slower as it takes three instructions to load a zero extended
>>>> 32-bit
>>>> pointer verses two for n32-2GB.
>>>
>>>
>>> And of course such code will only run on 64-bit processors that not only
>>> support 64-bit data, but 64-bit addressing as well.
>>
>>
>> That's right. All of this assumes a fully 64-bit operating system kernel
>> (Linux).
>>
>> It is not really very interesting on 'small' systems that have less than
>> about 1GB of RAM. And obviously impossible if 64-bit addressing is not
>> supported.
>>
>> So the interesting use cases are 'modern' systems with 4GB or more of ram
>> installed. And only then for the subset of applications that need more than
>> 2GB of virtual address space but will never need to consider more than 4GB.
>>
>>
>>
>>
>>> That is implement the
>>> CP0.Status.UX bit rather than CP0.Status.PX only -- the latters are still
>>> compatible with the true n32 ABI. See also CP0.Config.AT.
>>>
>>> Maciej
>>>
>>>
>>
>>
>
>
next prev parent reply other threads:[~2012-10-10 18:09 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-10 6:32 2GB userspace limitation in ABI N32 Ronny Meeus
2012-10-10 8:07 ` Ralf Baechle
2012-10-10 12:57 ` Rich Felker
2012-10-10 16:56 ` David Daney
2012-10-10 17:10 ` Maciej W. Rozycki
2012-10-10 17:34 ` David Daney
2012-10-10 17:49 ` Ronny Meeus
2012-10-10 18:08 ` David Daney [this message]
2012-10-10 15:12 ` Ronny Meeus
2012-10-12 10:18 ` Ralf Baechle
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