lkml.org 
[lkml]   [2015]   [Feb]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/2] powerpc/kvm: Enable running guests on RT Linux
On 02/26/2015 02:02 PM, Paolo Bonzini wrote:
>
>
> On 24/02/2015 00:27, Scott Wood wrote:
>> This isn't a host PIC driver. It's guest PIC emulation, some of which
>> is indeed not suitable for a rawlock (in particular, openpic_update_irq
>> which loops on the number of vcpus, with a loop body that calls
>> IRQ_check() which loops over all pending IRQs).
>
> The question is what behavior is wanted of code that isn't quite
> RT-ready. What is preferred, bugs or bad latency?
>
> If the answer is bad latency (which can be avoided simply by not running
> KVM on a RT kernel in production), patch 1 can be applied. If the
can be applied *but* makes no difference if applied or not.

> answer is bugs, patch 1 is not upstream material.
>
> I myself prefer to have bad latency; if something takes a spinlock in
> atomic context, that spinlock should be raw. If it hurts (latency),
> don't do it (use the affected code).

The problem, that is fixed by this s/spin_lock/raw_spin_lock/, exists
only in -RT. There is no change upstream. In general we fix such things
in -RT first and forward the patches upstream if possible. This convert
thingy would be possible.
Bug fixing comes before latency no matter if RT or not. Converting
every lock into a rawlock is not always the answer.
Last thing I read from Scott is that he is not entirely sure if this is
the right approach or not and patch #1 was not acked-by him either.

So for now I wait for Scott's feedback and maybe a backtrace :)

>
> Paolo

Sebastian


\
 
 \ /
  Last update: 2015-02-26 15:01    [W:0.089 / U:0.820 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site