question about context switch on arm Linux

question about context switch on arm Linux

[caiyuqing]

hi, all.
I have some questions about context switch on arm Linux (my target is
ARMv7-a).
1. Does arm linux support FCSE to handle the context switch?
2. If using FCSE, that means the processes number limit is 128 and the
memory limit is 32MB per process, is that right?

Thanks
qing

Re: question about context switch on arm Linux

[Richard Cochran]

On Sun, Oct 21, 2012 at 02:02:42PM +0800, caiyuqing wrote:
> hi, all.
> I have some questions about context switch on arm Linux (my target is
> ARMv7-a).
> 1. Does arm linux support FCSE to handle the context switch?

No, mainline Linux does not support FCSE. However, you can use Gilles'
unoffical (but working) FCSE branches at

  http://git.xenomai.org/?p=ipipe-gch.git;a=summary

> 2. If using FCSE, that means the processes number limit is 128 and the
> memory limit is 32MB per process, is that right?

Yes and no.

Gilles' patches offer a "strict mode" and a "best effort" mode. The
strict mode does have the limitation, but the best effort mode does
not.

HTH,
Richard

Re: question about context switch on arm Linux

[caiyuqing]

于 2012年10月21日 15:44, Richard Cochran 写道:
> On Sun, Oct 21, 2012 at 02:02:42PM +0800, caiyuqing wrote:
>> hi, all.
>> I have some questions about context switch on arm Linux (my target is
>> ARMv7-a).
>> 1. Does arm linux support FCSE to handle the context switch?
> No, mainline Linux does not support FCSE. However, you can use Gilles'
> unoffical (but working) FCSE branches at
>
>    http://git.xenomai.org/?p=ipipe-gch.git;a=summary
>
>> 2. If using FCSE, that means the processes number limit is 128 and the
>> memory limit is 32MB per process, is that right?
> Yes and no.
>
> Gilles' patches offer a "strict mode" and a "best effort" mode. The
> strict mode does have the limitation, but the best effort mode does
> not.
>
> HTH,
> Richard
Richard, thanks for your reply.
mainline Linux doesn't support FCSE, if so, when kernel switch a process 
to another(these two process share the same virtual memory space), that 
means the vitrual-to-physical address should be remaped, TLB shuold be 
invalid, CACHE should be flushed, right?

qing

Re: question about context switch on arm Linux

[Richard Cochran]

On Sun, Oct 21, 2012 at 04:19:50PM +0800, caiyuqing wrote:
> Richard, thanks for your reply.
> mainline Linux doesn't support FCSE, if so, when kernel switch a
> process to another(these two process share the same virtual memory
> space), that means the vitrual-to-physical address should be
> remaped, TLB shuold be invalid, CACHE should be flushed, right?

Yes, and that is why you can measure quite a long context switching
time when running Linux on ARMv4/5.

Thanks,
Richard