* [Xenomai] shielding fully CPU or CORE
@ 2013-07-19 9:17 Skander Bahloul
2013-07-20 7:54 ` Jan Kiszka
0 siblings, 1 reply; 6+ messages in thread
From: Skander Bahloul @ 2013-07-19 9:17 UTC (permalink / raw)
To: xenomai
Dear Xenomai list members,
On a successful instal (but without NVIDIA driver, cf my previous message), I am now starting using Xenomai.
We need to :
1* shield fully a CPU or core, against the scheduler, interruption, etc
2* run a single thread on this isolated CPU or core
Step 2 is OK with the Xenomai API.
But how should I achieve step 1 ?
I did not find advice in the Xenomai documentation.
I guess it should be done with :
$ sudo shield -a 0-3 -m -1
Do you agree ?
When may I find detailed info on CPU shielding ?
Thanks,
Skander BAHLOUL
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Xenomai] shielding fully CPU or CORE
2013-07-19 9:17 [Xenomai] shielding fully CPU or CORE Skander Bahloul
@ 2013-07-20 7:54 ` Jan Kiszka
2013-07-20 8:31 ` Gilles Chanteperdrix
2013-07-22 8:00 ` Kai Bollue
0 siblings, 2 replies; 6+ messages in thread
From: Jan Kiszka @ 2013-07-20 7:54 UTC (permalink / raw)
To: Skander Bahloul; +Cc: xenomai
On 2013-07-19 11:17, Skander Bahloul wrote:
> Dear Xenomai list members,
>
> On a successful instal (but without NVIDIA driver, cf my previous message), I am now starting using Xenomai.
>
> We need to :
> 1* shield fully a CPU or core, against the scheduler, interruption, etc
> 2* run a single thread on this isolated CPU or core
>
> Step 2 is OK with the Xenomai API.
> But how should I achieve step 1 ?
>
> I did not find advice in the Xenomai documentation.
> I guess it should be done with :
> $ sudo shield -a 0-3 -m -1
>
> Do you agree ?
> When may I find detailed info on CPU shielding ?
With "shield fully", do you mean 99,9...% or true 100%? The latter is
not possible with current Linux kernels, thus also not with Xenomai. For
the former, try kernel parameter isocpus (to keep Linux off certain
cores), possibly in combination with xeno_hal.rthal_supported_cpus (to
limit Xenomai to those cores).
True CPU domination is possible via virtualization, e.g. I'm working on
such a solution. But you will not get a Linux process environment for
your RT task, rather a set of bare-metal CPU cores you will have to boot
up yourself. Also, a lot of noise comes from other shared resources
(besides the CPU core itself), like memory and specifically the links to
the I/O devices (PCI bridges/buses...). So no miracle to expect that way
as well, at least on x86.
Jan
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Xenomai] shielding fully CPU or CORE
2013-07-20 7:54 ` Jan Kiszka
@ 2013-07-20 8:31 ` Gilles Chanteperdrix
2013-07-20 8:39 ` Jan Kiszka
2013-07-22 8:00 ` Kai Bollue
1 sibling, 1 reply; 6+ messages in thread
From: Gilles Chanteperdrix @ 2013-07-20 8:31 UTC (permalink / raw)
To: Jan Kiszka; +Cc: Skander Bahloul, xenomai
On 07/20/2013 09:54 AM, Jan Kiszka wrote:
> On 2013-07-19 11:17, Skander Bahloul wrote:
>> Dear Xenomai list members,
>>
>> On a successful instal (but without NVIDIA driver, cf my previous message), I am now starting using Xenomai.
>>
>> We need to :
>> 1* shield fully a CPU or core, against the scheduler, interruption, etc
>> 2* run a single thread on this isolated CPU or core
>>
>> Step 2 is OK with the Xenomai API.
>> But how should I achieve step 1 ?
>>
>> I did not find advice in the Xenomai documentation.
>> I guess it should be done with :
>> $ sudo shield -a 0-3 -m -1
>>
>> Do you agree ?
>> When may I find detailed info on CPU shielding ?
>
> With "shield fully", do you mean 99,9...% or true 100%? The latter is
> not possible with current Linux kernels, thus also not with Xenomai. For
> the former, try kernel parameter isocpus (to keep Linux off certain
> cores), possibly in combination with xeno_hal.rthal_supported_cpus (to
> limit Xenomai to those cores).
Maybe a stupid idea, but can we not shutdown linux cpus, using cpu
hotplug, so as to have full isolation?
--
Gilles.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Xenomai] shielding fully CPU or CORE
2013-07-20 8:31 ` Gilles Chanteperdrix
@ 2013-07-20 8:39 ` Jan Kiszka
2013-07-20 8:45 ` Gilles Chanteperdrix
0 siblings, 1 reply; 6+ messages in thread
From: Jan Kiszka @ 2013-07-20 8:39 UTC (permalink / raw)
To: Gilles Chanteperdrix; +Cc: Skander Bahloul, xenomai
On 2013-07-20 10:31, Gilles Chanteperdrix wrote:
> On 07/20/2013 09:54 AM, Jan Kiszka wrote:
>
>> On 2013-07-19 11:17, Skander Bahloul wrote:
>>> Dear Xenomai list members,
>>>
>>> On a successful instal (but without NVIDIA driver, cf my previous
>>> message), I am now starting using Xenomai.
>>>
>>> We need to :
>>> 1* shield fully a CPU or core, against the scheduler, interruption, etc
>>> 2* run a single thread on this isolated CPU or core
>>>
>>> Step 2 is OK with the Xenomai API.
>>> But how should I achieve step 1 ?
>>>
>>> I did not find advice in the Xenomai documentation.
>>> I guess it should be done with :
>>> $ sudo shield -a 0-3 -m -1
>>>
>>> Do you agree ?
>>> When may I find detailed info on CPU shielding ?
>>
>> With "shield fully", do you mean 99,9...% or true 100%? The latter is
>> not possible with current Linux kernels, thus also not with Xenomai. For
>> the former, try kernel parameter isocpus (to keep Linux off certain
>> cores), possibly in combination with xeno_hal.rthal_supported_cpus (to
>> limit Xenomai to those cores).
>
>
> Maybe a stupid idea, but can we not shutdown linux cpus, using cpu
> hotplug, so as to have full isolation?
We can, but we will also have to
- reboot those CPUs
- handle switches to Linux on the isolated cores (e.g. by migrating
the task to a Linux core)
- handle changes to the mm that is in use on isolated cores (TLB
shotdowns)
- handle Linux signals sent to Xenomai tasks on isolated cores
And there might be more subtle traps when using a core under Xenomai
that is offline for Linux. Nothing is impossible, but this is surely not
straightforward.
Jan
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Xenomai] shielding fully CPU or CORE
2013-07-20 8:39 ` Jan Kiszka
@ 2013-07-20 8:45 ` Gilles Chanteperdrix
0 siblings, 0 replies; 6+ messages in thread
From: Gilles Chanteperdrix @ 2013-07-20 8:45 UTC (permalink / raw)
To: Jan Kiszka; +Cc: Skander Bahloul, xenomai
On 07/20/2013 10:39 AM, Jan Kiszka wrote:
> On 2013-07-20 10:31, Gilles Chanteperdrix wrote:
>> On 07/20/2013 09:54 AM, Jan Kiszka wrote:
>>
>>> On 2013-07-19 11:17, Skander Bahloul wrote:
>>>> Dear Xenomai list members,
>>>>
>>>> On a successful instal (but without NVIDIA driver, cf my previous
>>>> message), I am now starting using Xenomai.
>>>>
>>>> We need to :
>>>> 1* shield fully a CPU or core, against the scheduler, interruption, etc
>>>> 2* run a single thread on this isolated CPU or core
>>>>
>>>> Step 2 is OK with the Xenomai API.
>>>> But how should I achieve step 1 ?
>>>>
>>>> I did not find advice in the Xenomai documentation.
>>>> I guess it should be done with :
>>>> $ sudo shield -a 0-3 -m -1
>>>>
>>>> Do you agree ?
>>>> When may I find detailed info on CPU shielding ?
>>>
>>> With "shield fully", do you mean 99,9...% or true 100%? The latter is
>>> not possible with current Linux kernels, thus also not with Xenomai. For
>>> the former, try kernel parameter isocpus (to keep Linux off certain
>>> cores), possibly in combination with xeno_hal.rthal_supported_cpus (to
>>> limit Xenomai to those cores).
>>
>>
>> Maybe a stupid idea, but can we not shutdown linux cpus, using cpu
>> hotplug, so as to have full isolation?
>
> We can, but we will also have to
> - reboot those CPUs
> - handle switches to Linux on the isolated cores (e.g. by migrating
> the task to a Linux core)
> - handle changes to the mm that is in use on isolated cores (TLB
> shotdowns)
> - handle Linux signals sent to Xenomai tasks on isolated cores
>
> And there might be more subtle traps when using a core under Xenomai
> that is offline for Linux. Nothing is impossible, but this is surely not
> straightforward.
Indeed, it was a stupid idea.
--
Gilles.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Xenomai] shielding fully CPU or CORE
2013-07-20 7:54 ` Jan Kiszka
2013-07-20 8:31 ` Gilles Chanteperdrix
@ 2013-07-22 8:00 ` Kai Bollue
1 sibling, 0 replies; 6+ messages in thread
From: Kai Bollue @ 2013-07-22 8:00 UTC (permalink / raw)
To: xenomai
On 20.07.2013 09:54, Jan Kiszka wrote:
> On 2013-07-19 11:17, Skander Bahloul wrote:
>> Dear Xenomai list members,
>>
>> On a successful instal (but without NVIDIA driver, cf my previous message), I am now starting using Xenomai.
>>
>> We need to :
>> 1* shield fully a CPU or core, against the scheduler, interruption, etc
>> 2* run a single thread on this isolated CPU or core
>>
>> Step 2 is OK with the Xenomai API.
>> But how should I achieve step 1 ?
>>
>> I did not find advice in the Xenomai documentation.
>> I guess it should be done with :
>> $ sudo shield -a 0-3 -m -1
>>
>> Do you agree ?
>> When may I find detailed info on CPU shielding ?
> With "shield fully", do you mean 99,9...% or true 100%? The latter is
> not possible with current Linux kernels, thus also not with Xenomai. For
> the former, try kernel parameter isocpus (to keep Linux off certain
> cores), possibly in combination with xeno_hal.rthal_supported_cpus (to
> limit Xenomai to those cores).
If you use an AMD CPU with "Bulldozer" / "Piledriver" architecture, for
better latencies, it helps to keep Linux off of both cores on one
module, as they share certain ressources. E.g. use isolcpus=0,1 and bind
your Xenomai task to CPU0.
Regards,
Kai
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2013-07-22 8:00 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2013-07-19 9:17 [Xenomai] shielding fully CPU or CORE Skander Bahloul
2013-07-20 7:54 ` Jan Kiszka
2013-07-20 8:31 ` Gilles Chanteperdrix
2013-07-20 8:39 ` Jan Kiszka
2013-07-20 8:45 ` Gilles Chanteperdrix
2013-07-22 8:00 ` Kai Bollue
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