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

Chuck Lever III
2023-09-12T15:27:11Z

> On Sep 12, 2023, at 11:14 AM, Feng Tang <feng.tang@intel.com> 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@intel.com> 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@intel.com> 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@intel.com>
>>>>> | Closes: https://lore.kernel.org/oe-lkp/202309081306.3ecb3734-oliver.sang@intel.com
>
>>>> 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