From: Dennis Zhou <dennis@kernel.org>
To: "Ma, Yu" <yu.ma@intel.com>
Cc: "Liam.Howlett@Oracle.com" <Liam.Howlett@oracle.com>,
Dennis Zhou <dennis@kernel.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"Williams, Dan J" <dan.j.williams@intel.com>,
"Hansen, Dave" <dave.hansen@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"Zhu, Lipeng" <lipeng.zhu@intel.com>,
"Deng, Pan" <pan.deng@intel.com>,
"shakeelb@google.com" <shakeelb@google.com>,
"Li, Tianyou" <tianyou.li@intel.com>,
"Chen, Tim C" <tim.c.chen@intel.com>,
"tim.c.chen@linux.intel.com" <tim.c.chen@linux.intel.com>
Subject: Re: [PATCH v2] percpu-internal/pcpu_chunk: Re-layout pcpu_chunk structure to reduce false sharing
Date: Fri, 9 Jun 2023 11:20:58 -0700 [thread overview]
Message-ID: <ZINtij2HhIu9h9Wx@V92F7Y9K0C.lan> (raw)
In-Reply-To: <SN7PR11MB7590D5959AF7179137A314FEE153A@SN7PR11MB7590.namprd11.prod.outlook.com>
Hi Yu,
On Wed, Jun 07, 2023 at 03:02:32PM +0000, Ma, Yu wrote:
> Thanks Liam and Dennis for review, this is updated patch with comment around:
>
> > 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 | 8 +++++++-
> > 1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/percpu-internal.h b/mm/percpu-internal.h index
> > f9847c131998..ecc7be1ec876 100644
> > --- a/mm/percpu-internal.h
> > +++ b/mm/percpu-internal.h
> > @@ -41,10 +41,16 @@ 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 */
> > +
> > + /*
> > + * 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; /* base address of this chunk
> > */
> >
> > 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
>
Thanks for adding the comment, but would you mind adding
____cacheline_aligned_in_smp? Unless that's something we're trying to
avoid, I think this is a good use case for it both on the pcpu_chunk and
specifically on base_addr as that's what we're accessing without a lock.
Thanks,
Dennis
next prev parent reply other threads:[~2023-06-09 18:21 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 [this message]
2023-06-10 0:12 ` Ma, Yu
2023-06-10 3:07 ` [PATCH v3] " Yu Ma
2023-06-12 21:43 ` Andrew Morton
2023-06-12 21:55 ` Dennis Zhou
2023-06-13 17:41 ` Ma, Yu
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