* Slub support with PREEMPT_RT ?
@ 2010-11-17 16:18 Jean-Michel Hautbois
2010-11-18 1:23 ` Darren Hart
0 siblings, 1 reply; 5+ messages in thread
From: Jean-Michel Hautbois @ 2010-11-17 16:18 UTC (permalink / raw)
To: linux-rt-users
Hi !
I am wondering why SLUB isn't supported with PREEMPT_RT ?
I cannot find any info on that except the fact it is not working yet.
What do we have to do in order to support it ?
Thanks in advance,
JM
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Slub support with PREEMPT_RT ?
2010-11-17 16:18 Slub support with PREEMPT_RT ? Jean-Michel Hautbois
@ 2010-11-18 1:23 ` Darren Hart
2010-11-18 8:40 ` Peter Zijlstra
0 siblings, 1 reply; 5+ messages in thread
From: Darren Hart @ 2010-11-18 1:23 UTC (permalink / raw)
To: Jean-Michel Hautbois; +Cc: linux-rt-users, Peter Zijlstra
On 11/17/2010 08:18 AM, Jean-Michel Hautbois wrote:
> Hi !
>
> I am wondering why SLUB isn't supported with PREEMPT_RT ?
> I cannot find any info on that except the fact it is not working yet.
> What do we have to do in order to support it ?
Peter can answer this better than I can, but it has something to do with
all the local_bh_disable() calls not being compatible with the goals of
PREEMPT_RT - if I remember correctly.
--
Darren Hart
Yocto Linux Kernel
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Slub support with PREEMPT_RT ?
2010-11-18 1:23 ` Darren Hart
@ 2010-11-18 8:40 ` Peter Zijlstra
2010-11-18 8:59 ` Jean-Michel Hautbois
0 siblings, 1 reply; 5+ messages in thread
From: Peter Zijlstra @ 2010-11-18 8:40 UTC (permalink / raw)
To: Darren Hart; +Cc: Jean-Michel Hautbois, linux-rt-users
On Wed, 2010-11-17 at 17:23 -0800, Darren Hart wrote:
> On 11/17/2010 08:18 AM, Jean-Michel Hautbois wrote:
> > Hi !
> >
> > I am wondering why SLUB isn't supported with PREEMPT_RT ?
> > I cannot find any info on that except the fact it is not working yet.
> > What do we have to do in order to support it ?
>
> Peter can answer this better than I can, but it has something to do with
> all the local_bh_disable() calls not being compatible with the goals of
> PREEMPT_RT - if I remember correctly.
Nah, its slub doens't use the softirq crap. But its close, you have to
iron out the per-cpu assumptions in the thing. I did a few slub-rt ports
at various times but the thing kept changing too much and I gave up.
I should probably do a new port and hope the thing is more stable now
that the excitement is down or somesuch.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Slub support with PREEMPT_RT ?
2010-11-18 8:40 ` Peter Zijlstra
@ 2010-11-18 8:59 ` Jean-Michel Hautbois
2010-11-18 11:04 ` Peter Zijlstra
0 siblings, 1 reply; 5+ messages in thread
From: Jean-Michel Hautbois @ 2010-11-18 8:59 UTC (permalink / raw)
To: Peter Zijlstra; +Cc: Darren Hart, linux-rt-users
2010/11/18 Peter Zijlstra <peterz@infradead.org>:
> On Wed, 2010-11-17 at 17:23 -0800, Darren Hart wrote:
>> On 11/17/2010 08:18 AM, Jean-Michel Hautbois wrote:
>> > Hi !
>> >
>> > I am wondering why SLUB isn't supported with PREEMPT_RT ?
>> > I cannot find any info on that except the fact it is not working yet.
>> > What do we have to do in order to support it ?
>>
>> Peter can answer this better than I can, but it has something to do with
>> all the local_bh_disable() calls not being compatible with the goals of
>> PREEMPT_RT - if I remember correctly.
>
> Nah, its slub doens't use the softirq crap. But its close, you have to
> iron out the per-cpu assumptions in the thing. I did a few slub-rt ports
> at various times but the thing kept changing too much and I gave up.
>
> I should probably do a new port and hope the thing is more stable now
> that the excitement is down or somesuch.
>
My real question is the impact of SLUB compared to SLAB on the
determinism of kmalloc usage and all caches.
I did some tests using SLUB instead of SLAB on a small (MPC5200 /
400Mhz / 16k i-cache and 16k d-cache), and slub seems to be better.
But I don't know if there is a possibility to tune SLAB in order to
get good results.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: Slub support with PREEMPT_RT ?
2010-11-18 8:59 ` Jean-Michel Hautbois
@ 2010-11-18 11:04 ` Peter Zijlstra
0 siblings, 0 replies; 5+ messages in thread
From: Peter Zijlstra @ 2010-11-18 11:04 UTC (permalink / raw)
To: Jean-Michel Hautbois; +Cc: Darren Hart, linux-rt-users
On Thu, 2010-11-18 at 09:59 +0100, Jean-Michel Hautbois wrote:
>
> My real question is the impact of SLUB compared to SLAB on the
> determinism of kmalloc usage and all caches.
> I did some tests using SLUB instead of SLAB on a small (MPC5200 /
> 400Mhz / 16k i-cache and 16k d-cache), and slub seems to be better.
> But I don't know if there is a possibility to tune SLAB in order to
> get good results.
That's a pretty pointless idea, non of them are deterministic allocators
-- nor can they be, page allocation involves the whole vm reclaim path.
If you want determinism don't allocate memory.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2010-11-18 11:04 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2010-11-17 16:18 Slub support with PREEMPT_RT ? Jean-Michel Hautbois
2010-11-18 1:23 ` Darren Hart
2010-11-18 8:40 ` Peter Zijlstra
2010-11-18 8:59 ` Jean-Michel Hautbois
2010-11-18 11:04 ` Peter Zijlstra
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