lkml.org 
[lkml]   [2011]   [Feb]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC][PATCH 0/4] ftrace: Use -mfentry when supported (this is for x86_64 right now)
On 02/18/2011 02:39 PM, Andi Kleen wrote:
> On Fri, Feb 18, 2011 at 03:10:18PM -0500, Dominique Toupin wrote:
>>
>> My understanding is stop_machine will stop all processors for many ms.
>
> I haven't measured it recently, but as long as the callback inside stop
> machine is short it definitely shouldn't be "many ms". The latency
> is bound by how long each CPU needs to answer to an interrupt, so if
> you have some code that disables interrupts for a long time it will take
> long -- but then your realtime response will be already bad.
>
> The interrupts are also done in parallel, so the interrupt latencies
> don't add up.
>
> If all the CPUs answer in a reasonable time it's still not a cheap
> operation, but nothing that takes "many ms". Most likely it's fine
> for most soft real time purposes.
>

We should also be able to use the breakpoint hack to avoid holding all
the CPUs. They still need to be interrupted, but that skips the
rendezvous operation.

-hpa



\
 
 \ /
  Last update: 2011-02-18 23:49    [W:0.964 / U:0.036 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site