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Message-ID: <alpine.DEB.2.00.1004071130260.13261@router.home>
Date: Wed, 7 Apr 2010 11:43:21 -0500 (CDT)
From: Christoph Lameter <cl@...ux-foundation.org>
To: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
cc: Eric Dumazet <eric.dumazet@...il.com>,
netdev <netdev@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
Pekka Enberg <penberg@...helsinki.fi>, alex.shi@...el.com,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Ma, Ling" <ling.ma@...el.com>,
"Chen, Tim C" <tim.c.chen@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: hackbench regression due to commit 9dfc6e68bfe6e
On Wed, 7 Apr 2010, Zhang, Yanmin wrote:
> I collected retired instruction, dtlb miss and LLC miss.
> Below is data of LLC miss.
>
> Kernel 2.6.33:
> 20.94% hackbench [kernel.kallsyms] [k] copy_user_generic_string
> 14.56% hackbench [kernel.kallsyms] [k] unix_stream_recvmsg
> 12.88% hackbench [kernel.kallsyms] [k] kfree
> 7.37% hackbench [kernel.kallsyms] [k] kmem_cache_free
> 7.18% hackbench [kernel.kallsyms] [k] kmem_cache_alloc_node
> 6.78% hackbench [kernel.kallsyms] [k] kfree_skb
> 6.27% hackbench [kernel.kallsyms] [k] __kmalloc_node_track_caller
> 2.73% hackbench [kernel.kallsyms] [k] __slab_free
> 2.21% hackbench [kernel.kallsyms] [k] get_partial_node
> 2.01% hackbench [kernel.kallsyms] [k] _raw_spin_lock
> 1.59% hackbench [kernel.kallsyms] [k] schedule
> 1.27% hackbench hackbench [.] receiver
> 0.99% hackbench libpthread-2.9.so [.] __read
> 0.87% hackbench [kernel.kallsyms] [k] unix_stream_sendmsg
>
> Kernel 2.6.34-rc3:
> 18.55% hackbench [kernel.kallsyms] [k] copy_user_generic_str
> ing
> 13.19% hackbench [kernel.kallsyms] [k] unix_stream_recvmsg
> 11.62% hackbench [kernel.kallsyms] [k] kfree
> 8.54% hackbench [kernel.kallsyms] [k] kmem_cache_free
> 7.88% hackbench [kernel.kallsyms] [k] __kmalloc_node_track_
> caller
Seems that the overhead of __kmalloc_node_track_caller was increased. The
function inlines slab_alloc().
> 6.54% hackbench [kernel.kallsyms] [k] kmem_cache_alloc_node
> 5.94% hackbench [kernel.kallsyms] [k] kfree_skb
> 3.48% hackbench [kernel.kallsyms] [k] __slab_free
> 2.15% hackbench [kernel.kallsyms] [k] _raw_spin_lock
> 1.83% hackbench [kernel.kallsyms] [k] schedule
> 1.82% hackbench [kernel.kallsyms] [k] get_partial_node
> 1.59% hackbench hackbench [.] receiver
> 1.37% hackbench libpthread-2.9.so [.] __read
I wonder if this is not related to the kmem_cache_cpu structure straggling
cache line boundaries under some conditions. On 2.6.33 the kmem_cache_cpu
structure was larger and therefore tight packing resulted in different
alignment.
Could you see how the following patch affects the results. It attempts to
increase the size of kmem_cache_cpu to a power of 2 bytes. There is also
the potential that other per cpu fetches to neighboring objects affect the
situation. We could cacheline align the whole thing.
---
include/linux/slub_def.h | 5 +++++
1 file changed, 5 insertions(+)
Index: linux-2.6/include/linux/slub_def.h
===================================================================
--- linux-2.6.orig/include/linux/slub_def.h 2010-04-07 11:33:50.000000000 -0500
+++ linux-2.6/include/linux/slub_def.h 2010-04-07 11:35:18.000000000 -0500
@@ -38,6 +38,11 @@ struct kmem_cache_cpu {
void **freelist; /* Pointer to first free per cpu object */
struct page *page; /* The slab from which we are allocating */
int node; /* The node of the page (or -1 for debug) */
+#ifndef CONFIG_64BIT
+ int dummy1;
+#endif
+ unsigned long dummy2;
+
#ifdef CONFIG_SLUB_STATS
unsigned stat[NR_SLUB_STAT_ITEMS];
#endif
--
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