Re: [linus:master] [shmem] a2e459555c: aim9.disk_src.ops_per_sec -19.0% regression

Chuck Lever III
2023-09-13T13:33:05Z

> On Sep 13, 2023, at 2:47 AM, Feng Tang <feng.tang@intel.com> wrote:
>
> On Tue, Sep 12, 2023 at 11:14:42PM +0800, Tang, Feng wrote:
> [...]
>>>
>>> Well that's the problem. Since I can't run the reproducer, there's
>>> nothing I can do to troubleshoot the problem myself.
>>
>> We dug more into the perf and other profiling data from 0Day server
>> running this case, and it seems that the new simple_offset_add()
>> called by shmem_mknod() brings extra cost related with slab,
>> specifically the 'radix_tree_node', which cause the regression.
>>
>> Here is some slabinfo diff for commit a2e459555c5f and its parent:
>>
>> 23a31d87645c6527 a2e459555c5f9da3e619b7e47a6
>> ---------------- ---------------------------
>>
>> 26363 +40.2% 36956 slabinfo.radix_tree_node.active_objs
>> 941.00 +40.4% 1321 slabinfo.radix_tree_node.active_slabs
>> 26363 +40.3% 37001 slabinfo.radix_tree_node.num_objs
>> 941.00 +40.4% 1321 slabinfo.radix_tree_node.num_slabs
>>
>> Also the perf profile show some difference
>>
>> 0.01 ±223% +0.1 0.10 ± 28% pp.self.shuffle_freelist
>> 0.00 +0.1 0.11 ± 40% pp.self.xas_create
>> 0.00 +0.1 0.12 ± 27% pp.self.xas_find_marked
>> 0.00 +0.1 0.14 ± 18% pp.self.xas_alloc
>> 0.03 ±103% +0.1 0.17 ± 29% pp.self.xas_descend
>> 0.00 +0.2 0.16 ± 23% pp.self.xas_expand
>> 0.10 ± 22% +0.2 0.27 ± 16% pp.self.rcu_segcblist_enqueue
>> 0.92 ± 35% +0.3 1.22 ± 11% pp.self.kmem_cache_free
>> 0.00 +0.4 0.36 ± 16% pp.self.xas_store
>> 0.32 ± 30% +0.4 0.71 ± 12% pp.self.__call_rcu_common
>> 0.18 ± 27% +0.5 0.65 ± 8% pp.self.kmem_cache_alloc_lru
>> 0.36 ± 79% +0.6 0.96 ± 15% pp.self.__slab_free
>> 0.00 +0.8 0.80 ± 14% pp.self.radix_tree_node_rcu_free
>> 0.00 +1.0 1.01 ± 16% pp.self.radix_tree_node_ctor
>>
>> Some perf profile from a2e459555c5f is:
>>
>> - 17.09% 0.09% singleuser [kernel.kallsyms] [k] path_openat
>> - 16.99% path_openat
>> - 12.23% open_last_lookups
>> - 11.33% lookup_open.isra.0
>> - 9.05% shmem_mknod
>> - 5.11% simple_offset_add
>> - 4.95% __xa_alloc_cyclic
>> - 4.88% __xa_alloc
>> - 4.76% xas_store
>> - xas_create
>> - 2.40% xas_expand.constprop.0
>> - 2.01% xas_alloc
>> - kmem_cache_alloc_lru
>> - 1.28% ___slab_alloc
>> - 1.22% allocate_slab
>> - 1.19% shuffle_freelist
>> - 1.04% setup_object
>> radix_tree_node_ctor
>>
>> Please let me know if you need more info.
>>
>>>
>>> Is there any hope in getting this reproducer to run on Fedora?
>>
>> Myself haven't succeeded to reproduce it locally, will keep trying
>> it tomorrow.
>
> It can be reproduced on a local machien with CentOS 9 (similar to
> Fedora ?),

Excellent, I appreciate this!

> and some steps as:
>
> * download source code
> $ wget https://sourceforge.net/projects/aimbench/files/aim-suite9/Initial%20release/s9110.tar.Z
>
> * untar the file and run 'make'
>
> * create 2 files 's9workfile' and 'test.config'
>
> $ cat s9workfile
> # @(#) s9workfile:1.2 1/22/96 00:00:00
> # AIM Independent Resource Benchmark - Suite IX Workfile
> FILESIZE: 5M
> disk_src
>
> $ cat test.config
> test
> disk_src
> 200s
> /dev/shm/
>
> * run the test with cmd "./singleuser -nl < test.config"
>
> The test case here is 'disk_src', so I picked one file 'disk_src.c'
> and attached it for quick reference.
>
> The kernel config of my CentOS is different from what 0Day used, so
> the perf-profile and peformance score are a little different, but
> the regression trend is the same, that commit a2e459555c5f has about
> 20% drop.
>
> Also the test platform doesn't matter, I tried on several generation
> of Xeon servers which can all reproduce it.

--
Chuck Lever