On Wed, 22 Jul 2015 06:26:42 +0000
"Koehrer Mathias (ETAS/ESW5)" [off-list ref] wrote:

Hi all,

quoted

quoted

quoted

similar situation here with 3.18.11-rt7. The problem occurred once so far.

Is this _with_ or _without_ the patch in question?

With the patch. slub_delay_ctor_on_rt.patch is applied. It is 3.18.11-rt7 with
additional drivers
for our hardware.

Since I have removed the slub_delay_ctor_on_rt.patch from 3.18.13-rt10 I have never seen this issue anymore on our systems.

From my files, that is this patch:

----
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: slub: delay ctor until the object is requested

It seems that allocation of plenty objects causes latency on ARM since that code can not be preempted

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 mm/slub.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/mm/slub.c
+++ b/mm/slub.c

@@ -1376,8 +1376,10 @@ static void setup_object(struct kmem_cac
                                void *object)
 {
        setup_object_debug(s, page, object);
+#ifndef CONFIG_PREEMPT_RT_FULL
        if (unlikely(s->ctor))
                s->ctor(object);
+#endif
 }
 
 static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)

@@ -2499,6 +2501,10 @@ static __always_inline void *slab_alloc_
 
        if (unlikely(gfpflags & __GFP_ZERO) && object)
                memset(object, 0, s->object_size);
+#ifdef CONFIG_PREEMPT_RT_FULL
+       if (unlikely(s->ctor) && object)
+               s->ctor(object);
+#endif
 
        slab_post_alloc_hook(s, gfpflags, object);
----

Now I had a look at the latest 3.18.17-rt14: Here I do not see that patch anymore.

It's still there. Note, that when I pull -rt into stable, I do a
 git quiltimport, which renames the patch set. It's now called:

 0089-slub-delay-ctor-until-the-object-is-requested.patch

-- Steve

Has it been removed from the patchset? 
Is there still a need to ignore one of the patches?
Neither in the announcement to 3.18.16-rt13 nor to 3.18.17-rt14 I read any comment on that.

Regards

Mathias