From: Yu Ma <yu.ma@intel.com>
To: dennis@kernel.org, Liam.Howlett@oracle.com
Cc: akpm@linux-foundation.org, dan.j.williams@intel.com,
dave.hansen@intel.com, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, lipeng.zhu@intel.com, pan.deng@intel.com,
shakeelb@google.com, tianyou.li@intel.com, tim.c.chen@intel.com,
tim.c.chen@linux.intel.com, yu.ma@intel.com
Subject: [PATCH v3] percpu-internal/pcpu_chunk: Re-layout pcpu_chunk structure to reduce false sharing
Date: Fri, 9 Jun 2023 23:07:30 -0400 [thread overview]
Message-ID: <20230610030730.110074-1-yu.ma@intel.com> (raw)
In-Reply-To: <ZINtij2HhIu9h9Wx@V92F7Y9K0C.lan>
When running UnixBench/Execl throughput case, false sharing is observed
due to frequent read on base_addr and write on free_bytes, chunk_md.
UnixBench/Execl represents a class of workload where bash scripts
are spawned frequently to do some short jobs. It will do system call on
execl frequently, and execl will call mm_init to initialize mm_struct
of the process. mm_init will call __percpu_counter_init for
percpu_counters initialization. Then pcpu_alloc is called to read
the base_addr of pcpu_chunk for memory allocation. Inside pcpu_alloc,
it will call pcpu_alloc_area to allocate memory from a specified chunk.
This function will update "free_bytes" and "chunk_md" to record the
rest free bytes and other meta data for this chunk. Correspondingly,
pcpu_free_area will also update these 2 members when free memory.
Call trace from perf is as below:
+ 57.15% 0.01% execl [kernel.kallsyms] [k] __percpu_counter_init
+ 57.13% 0.91% execl [kernel.kallsyms] [k] pcpu_alloc
- 55.27% 54.51% execl [kernel.kallsyms] [k] osq_lock
- 53.54% 0x654278696e552f34
main
__execve
entry_SYSCALL_64_after_hwframe
do_syscall_64
__x64_sys_execve
do_execveat_common.isra.47
alloc_bprm
mm_init
__percpu_counter_init
pcpu_alloc
- __mutex_lock.isra.17
In current pcpu_chunk layout, ‘base_addr’ is in the same cache line
with ‘free_bytes’ and ‘chunk_md’, and ‘base_addr’ is at the
last 8 bytes. This patch moves ‘bound_map’ up to ‘base_addr’,
to let ‘base_addr’ locate in a new cacheline.
With this change, on Intel Sapphire Rapids 112C/224T platform,
based on v6.4-rc4, the 160 parallel score improves by 24%.
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Yu Ma <yu.ma@intel.com>
---
mm/percpu-internal.h | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/mm/percpu-internal.h b/mm/percpu-internal.h
index f9847c131998..7f108b25bb93 100644
--- a/mm/percpu-internal.h
+++ b/mm/percpu-internal.h
@@ -41,10 +41,17 @@ struct pcpu_chunk {
struct list_head list; /* linked to pcpu_slot lists */
int free_bytes; /* free bytes in the chunk */
struct pcpu_block_md chunk_md;
- void *base_addr; /* base address of this chunk */
+ unsigned long *bound_map; /* boundary map */
+
+ /*
+ * base_addr is the base address of this chunk.
+ * To reduce false sharing, current layout is optimized to make sure
+ * base_addr locate in the different cacheline with free_bytes and
+ * chunk_md.
+ */
+ void *base_addr ____cacheline_aligned_in_smp;
unsigned long *alloc_map; /* allocation map */
- unsigned long *bound_map; /* boundary map */
struct pcpu_block_md *md_blocks; /* metadata blocks */
void *data; /* chunk data */
--
2.39.3
next prev parent reply other threads:[~2023-06-10 2:40 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-06 12:54 [PATCH] percpu-internal/pcpu_chunk: Re-layout pcpu_chunk structure to reduce false sharing Yu Ma
2023-06-06 19:21 ` Liam R. Howlett
2023-06-06 21:25 ` Dennis Zhou
2023-06-07 12:50 ` Ma, Yu
2023-06-07 14:50 ` [PATCH v2] " Yu Ma
2023-06-07 15:02 ` Ma, Yu
2023-06-09 18:20 ` Dennis Zhou
2023-06-10 0:12 ` Ma, Yu
2023-06-10 3:07 ` Yu Ma [this message]
2023-06-12 21:43 ` [PATCH v3] " Andrew Morton
2023-06-12 21:55 ` Dennis Zhou
2023-06-13 17:41 ` Ma, Yu
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