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

[Chuck Lever III]

> On Sep 12, 2023, at 11:14 AM, Feng Tang <feng.tang@xxxxxxxxx> wrote:
> 
> Hi Chuck Lever, 
> 
> On Tue, Sep 12, 2023 at 09:01:29PM +0800, Chuck Lever III wrote:
>> 
>> 
>>> On Sep 11, 2023, at 9:25 PM, Oliver Sang <oliver.sang@xxxxxxxxx> wrote:
>>> 
>>> hi, Chuck Lever,
>>> 
>>> On Fri, Sep 08, 2023 at 02:43:22PM +0000, Chuck Lever III wrote:
>>>> 
>>>> 
>>>>> On Sep 8, 2023, at 1:26 AM, kernel test robot <oliver.sang@xxxxxxxxx> wrote:
>>>>> 
>>>>> 
>>>>> 
>>>>> Hello,
>>>>> 
>>>>> kernel test robot noticed a -19.0% regression of aim9.disk_src.ops_per_sec on:
>>>>> 
>>>>> 
>>>>> commit: a2e459555c5f9da3e619b7e47a63f98574dc75f1 ("shmem: stable directory offsets")
>>>>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>>>>> 
>>>>> testcase: aim9
>>>>> test machine: 48 threads 2 sockets Intel(R) Xeon(R) CPU E5-2697 v2 @ 2.70GHz (Ivy Bridge-EP) with 112G memory
>>>>> parameters:
>>>>> 
>>>>> testtime: 300s
>>>>> test: disk_src
>>>>> cpufreq_governor: performance
>>>>> 
>>>>> 
>>>>> In addition to that, the commit also has significant impact on the following tests:
>>>>> 
>>>>> +------------------+-------------------------------------------------------------------------------------------------+
>>>>> | testcase: change | aim9: aim9.disk_src.ops_per_sec -14.6% regression                                               |
>>>>> | test machine     | 48 threads 2 sockets Intel(R) Xeon(R) CPU E5-2697 v2 @ 2.70GHz (Ivy Bridge-EP) with 112G memory |
>>>>> | test parameters  | cpufreq_governor=performance                                                                    |
>>>>> |                  | test=all                                                                                        |
>>>>> |                  | testtime=5s                                                                                     |
>>>>> +------------------+-------------------------------------------------------------------------------------------------+
>>>>> 
>>>>> 
>>>>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>>>>> the same patch/commit), kindly add following tags
>>>>> | Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
>>>>> | Closes: https://lore.kernel.org/oe-lkp/202309081306.3ecb3734-oliver.sang@xxxxxxxxx
> 
>>>> But, I'm still in a position where I can't run this test,
>>>> and the results don't really indicate where the problem
>>>> is. So I can't possibly address this issue.
>>>> 
>>>> Any suggestions, advice, or help would be appreciated.
>>> 
>>> if you have further fix patch, could you let us know? I will test it.
>> 
>> 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.

Thank you! Will ponder.


> 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.
> 
> Thanks,
> Feng
> 
>> 
>> --
>> Chuck Lever


--
Chuck Lever