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Howlett" To: Yu Ma Cc: akpm@linux-foundation.org, tim.c.chen@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, dave.hansen@intel.com, dan.j.williams@intel.com, shakeelb@google.com, pan.deng@intel.com, tianyou.li@intel.com, lipeng.zhu@intel.com, tim.c.chen@linux.intel.com Subject: Re: [PATCH] percpu-internal/pcpu_chunk: Re-layout pcpu_chunk structure to reduce false sharing Message-ID: <20230606192127.w66indpq74ec6eyt@revolver> Mail-Followup-To: "Liam R. Howlett" , Yu Ma , akpm@linux-foundation.org, tim.c.chen@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, dave.hansen@intel.com, dan.j.williams@intel.com, shakeelb@google.com, pan.deng@intel.com, tianyou.li@intel.com, lipeng.zhu@intel.com, tim.c.chen@linux.intel.com References: <20230606125404.95256-1-yu.ma@intel.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: <20230606125404.95256-1-yu.ma@intel.com> User-Agent: NeoMutt/20220429 X-ClientProxiedBy: YT4PR01CA0039.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:fe::28) To SN6PR10MB3022.namprd10.prod.outlook.com (2603:10b6:805:d8::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SN6PR10MB3022:EE_|DS0PR10MB7363:EE_ X-MS-Office365-Filtering-Correlation-Id: 99c0ad72-edff-40b0-8e5e-08db66c33b73 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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score=0 suspectscore=0 malwarescore=0 mlxscore=0 bulkscore=0 phishscore=0 mlxlogscore=999 spamscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2305260000 definitions=main-2306060165 X-Proofpoint-GUID: PQUDaUj4y2x5F92g4wN56aJgPJYcIVA4 X-Proofpoint-ORIG-GUID: PQUDaUj4y2x5F92g4wN56aJgPJYcIVA4 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Yu Ma [230606 08:27]: > When running UnixBench/Execl throughput case, false sharing is observed > due to frequent read on base_addr and write on free_bytes, chunk_md. >=20 > 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 >=20 > In current pcpu_chunk layout, =E2=80=98base_addr=E2=80=99 is in the same = cache line > with =E2=80=98free_bytes=E2=80=99 and =E2=80=98chunk_md=E2=80=99, and =E2= =80=98base_addr=E2=80=99 is at the=20 > last 8 bytes. This patch moves =E2=80=98bound_map=E2=80=99 up to =E2=80= =98base_addr=E2=80=99, > to let =E2=80=98base_addr=E2=80=99 locate in a new cacheline. >=20 > With this change, on Intel Sapphire Rapids 112C/224T platform, > based on v6.4-rc4, the 160 parallel score improves by 24%. Can we have a comment somewhere around this structure to avoid someone reverting this change by accident? >=20 > Reviewed-by: Tim Chen > Signed-off-by: Yu Ma > --- > mm/percpu-internal.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) >=20 > diff --git a/mm/percpu-internal.h b/mm/percpu-internal.h > index f9847c131998..981eeb2ad0a9 100644 > --- a/mm/percpu-internal.h > +++ b/mm/percpu-internal.h > @@ -41,10 +41,10 @@ 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; > + unsigned long *bound_map; /* boundary map */ > void *base_addr; /* base address of this chunk */ > =20 > unsigned long *alloc_map; /* allocation map */ > - unsigned long *bound_map; /* boundary map */ > struct pcpu_block_md *md_blocks; /* metadata blocks */ > =20 > void *data; /* chunk data */ > --=20 > 2.39.3 >=20