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Message-ID: <262c742f-dc0c-4adc-b23c-047cd3298a5e@amd.com>
Date: Thu, 16 Oct 2025 20:46:29 +0530
From: "D, Suneeth" <Suneeth.D@....com>
To: Vlastimil Babka <vbabka@...e.cz>, Suren Baghdasaryan <surenb@...gle.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>, Christoph Lameter
<cl@...two.org>, David Rientjes <rientjes@...gle.com>
CC: Roman Gushchin <roman.gushchin@...ux.dev>, Harry Yoo
<harry.yoo@...cle.com>, Uladzislau Rezki <urezki@...il.com>, Sidhartha Kumar
<sidhartha.kumar@...cle.com>, <linux-mm@...ck.org>,
<linux-kernel@...r.kernel.org>, <rcu@...r.kernel.org>,
<maple-tree@...ts.infradead.org>
Subject: Re: [PATCH v8 15/23] maple_tree: use percpu sheaves for
maple_node_cache
Hi Vlastimil Babka,
On 9/10/2025 1:31 PM, Vlastimil Babka wrote:
> Setup the maple_node_cache with percpu sheaves of size 32 to hopefully
> improve its performance. Note this will not immediately take advantage
> of sheaf batching of kfree_rcu() operations due to the maple tree using
> call_rcu with custom callbacks. The followup changes to maple tree will
> change that and also make use of the prefilled sheaves functionality.
>
We run will-it-scale-process-mmap2 micro-benchmark as part of our weekly
CI for Kernel Performance Regression testing between a stable vs rc
kernel. In this week's run we were able to observe severe regression on
AMD platforms (Turin and Bergamo) with running the micro-benchmark
between the kernels v6.17 and v6.18-rc1 in the range of 12-13% (Turin)
and 22-26% (Bergamo). Bisecting further landed me onto this commit
(59faa4da7cd4565cbce25358495556b75bb37022) as first bad commit. The
following were the machines' configuration and test parameters used:-
Model name: AMD EPYC 128-Core Processor [Bergamo]
Thread(s) per core: 2
Core(s) per socket: 128
Socket(s): 1
Total online memory: 258G
Model name: AMD EPYC 64-Core Processor [Turin]
Thread(s) per core: 2
Core(s) per socket: 64
Socket(s): 1
Total online memory: 258G
Test params:
nr_task: [1 8 64 128 192 256]
mode: process
test: mmap2
kpi: per_process_ops
cpufreq_governor: performance
The following are the stats after bisection:-
(the KPI used here is per_process_ops)
kernel_versions per_process_ops
--------------- ---------------
v6.17.0 - 258291
v6.18.0-rc1 - 225839
v6.17.0-rc3-59faa4da7 - 212152
v6.17.0-rc3-3accabda4da1(one commit before bad commit) - 265054
Recreation steps:
1) git clone https://github.com/antonblanchard/will-it-scale.git
2) git clone https://github.com/intel/lkp-tests.git
3) cd will-it-scale && git apply
lkp-tests/programs/will-it-scale/pkg/will-it-scale.patch
4) make
5) python3 runtest.py mmap2 25 process 0 0 1 8 64 128 192 256
NOTE: [5] is specific to machine's architecture. starting from 1 is the
array of no.of tasks that you'd wish to run the testcase which here is
no.cores per CCX, per NUMA node/ per Socket, nr_threads.
I also ran the micro-benchmark with tools/testing/perf record and
following is the collected data:-
# perf diff perf.data.old perf.data
No kallsyms or vmlinux with build-id
0fc9c7b62ade1502af5d6a060914732523f367ef was found
Warning:
43 out of order events recorded.
Warning:
54 out of order events recorded.
# Event 'cycles:P'
#
# Baseline Delta Abs Shared Object Symbol
# ........ ......... ......................
..............................................
#
+51.51% [kernel.kallsyms] [k]
native_queued_spin_lock_slowpath
+14.39% [kernel.kallsyms] [k] perf_iterate_ctx
+2.52% [kernel.kallsyms] [k] unmap_page_range
+1.75% [kernel.kallsyms] [k] mas_wr_node_store
+1.47% [kernel.kallsyms] [k] __pi_memset
+1.38% [kernel.kallsyms] [k] mt_free_rcu
+1.36% [kernel.kallsyms] [k] free_pgd_range
+1.10% [kernel.kallsyms] [k] __pi_memcpy
+0.96% [kernel.kallsyms] [k] __kmem_cache_alloc_bulk
+0.92% [kernel.kallsyms] [k] __mmap_region
+0.79% [kernel.kallsyms] [k] mas_empty_area_rev
+0.74% [kernel.kallsyms] [k] __cond_resched
+0.73% [kernel.kallsyms] [k] mas_walk
+0.59% [kernel.kallsyms] [k] mas_pop_node
+0.57% [kernel.kallsyms] [k] perf_event_mmap_output
+0.49% [kernel.kallsyms] [k] mas_find
+0.48% [kernel.kallsyms] [k] mas_next_slot
+0.46% [kernel.kallsyms] [k] kmem_cache_free
+0.42% [kernel.kallsyms] [k] mas_leaf_max_gap
+0.42% [kernel.kallsyms] [k]
__call_rcu_common.constprop.0
+0.39% [kernel.kallsyms] [k] entry_SYSCALL_64
+0.38% [kernel.kallsyms] [k] mas_prev_slot
+0.38% [kernel.kallsyms] [k] kmem_cache_alloc_noprof
+0.37% [kernel.kallsyms] [k] mas_store_gfp
> Reviewed-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
> Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---
> lib/maple_tree.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index 4f0e30b57b0cef9e5cf791f3f64f5898752db402..d034f170ac897341b40cfd050b6aee86b6d2cf60 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -6040,9 +6040,14 @@ bool mas_nomem(struct ma_state *mas, gfp_t gfp)
>
> void __init maple_tree_init(void)
> {
> + struct kmem_cache_args args = {
> + .align = sizeof(struct maple_node),
> + .sheaf_capacity = 32,
> + };
> +
> maple_node_cache = kmem_cache_create("maple_node",
> - sizeof(struct maple_node), sizeof(struct maple_node),
> - SLAB_PANIC, NULL);
> + sizeof(struct maple_node), &args,
> + SLAB_PANIC);
> }
>
> /**
>
---
Thanks and Regards
Suneeth D
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