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From: Daniel Jordan <daniel.m.jordan@oracle.com>
To: "Elliott, Robert (Persistent Memory)" <elliott@hpe.com>
Cc: "'Daniel Jordan'" <daniel.m.jordan@oracle.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"aarcange@redhat.com" <aarcange@redhat.com>,
	"aaron.lu@intel.com" <aaron.lu@intel.com>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	"bsd@redhat.com" <bsd@redhat.com>,
	"darrick.wong@oracle.com" <darrick.wong@oracle.com>,
	"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
	"jgg@mellanox.com" <jgg@mellanox.com>,
	"jwadams@google.com" <jwadams@google.com>,
	"jiangshanlai@gmail.com" <jiangshanlai@gmail.com>,
	"mhocko@kernel.org" <mhocko@kernel.org>,
	"mike.kravetz@oracle.com" <mike.kravetz@oracle.com
Subject: Re: [RFC PATCH v4 11/13] mm: parallelize deferred struct page initialization within each node
Date: Tue, 27 Nov 2018 12:23:59 -0800
Message-ID: <20181127202359.biav42vbfchprmo5@ca-dmjordan1.us.oracle.com> (raw)
In-Reply-To: <AT5PR8401MB1169AA00F542BA2E3204FC24ABD00@AT5PR8401MB1169.NAMPRD84.PROD.OUTLOOK.COM>

On Tue, Nov 27, 2018 at 12:12:28AM +0000, Elliott, Robert (Persistent Memory) wrote:
> I ran a short test with:
> * HPE ProLiant DL360 Gen9 system
> * Intel Xeon E5-2699 CPU with 18 physical cores (0-17) and 
>   18 hyperthreaded cores (36-53)
> * DDR4 NVDIMM-Ns (which run at regular DRAM DIMM speeds)
> * fio workload generator
> * cores on one CPU socket talking to a pmem device on the same CPU
> * large (1 MiB) random writes (to minimize the threads getting CPU cache
>   hits from each other)
> 
> Results:
> * 31.7 GB/s    four threads, four physical cores (0,1,2,3)
> * 22.2 GB/s    four threads, two physical cores (0,1,36,37)
> * 21.4 GB/s    two threads, two physical cores (0,1)
> * 12.1 GB/s    two threads, one physical core (0,36)
> * 11.2 GB/s    one thread, one physical core (0)
> 
> So, I think it's important that the initialization threads run on
> separate physical cores.

Thanks for running this.  And fair enough, in this test using both siblings
gives only a 4-8% speedup over one, so it makes sense to use only cores in the
calculation.

As for how to actually do this, some arches have smp_num_siblings, but there
should be a generic interface to provide that.

It's also possible to calculate this from the existing
topology_sibling_cpumask, but the first option is better IMHO.  Open to
suggestions.

> For the number of cores to use, one approach is:
>     memory bandwidth (number of interleaved channels * speed)
> divided by 
>     CPU core max sustained write bandwidth
> 
> For example, this 2133 MT/s system is roughly:
>     68 GB/s    (4 * 17 GB/s nominal)
> divided by
>     11.2 GB/s  (one core's performance)
> which is 
>     6 cores
> 
> ACPI HMAT will report that 68 GB/s number.  I'm not sure of
> a good way to discover the 11.2 GB/s number.

Yes, this would be nice to do if we could know the per-core number, with the
caveat that a single number like this would be most useful for the CPU-memory
pair it was calculated for, so the kernel could at least calculate it for jobs
operating on local memory.

Some BogoMIPS-like calibration may work, but I'll wait for ACPI HMAT support in
the kernel.

  reply index

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-05 16:55 [RFC PATCH v4 00/13] ktask: multithread CPU-intensive kernel work Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 01/13] ktask: add documentation Daniel Jordan
2018-11-05 21:19   ` Randy Dunlap
2018-11-06  2:27     ` Daniel Jordan
2018-11-06  8:49   ` Peter Zijlstra
2018-11-06 20:34     ` Daniel Jordan
2018-11-06 20:51       ` Jason Gunthorpe
2018-11-07 10:27         ` Peter Zijlstra
2018-11-07 20:21           ` Daniel Jordan
2018-11-07 10:35       ` Peter Zijlstra
2018-11-07 21:20         ` Daniel Jordan
2018-11-08 17:26   ` Jonathan Corbet
2018-11-08 19:15     ` Daniel Jordan
2018-11-08 19:24       ` Jonathan Corbet
2018-11-27 19:50   ` Pavel Machek
2018-11-28 16:56     ` Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 02/13] ktask: multithread CPU-intensive kernel work Daniel Jordan
2018-11-05 20:51   ` Randy Dunlap
2018-11-06  2:24     ` Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 03/13] ktask: add undo support Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 04/13] ktask: run helper threads at MAX_NICE Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 05/13] workqueue, ktask: renice helper threads to prevent starvation Daniel Jordan
2018-11-13 16:34   ` Tejun Heo
2018-11-19 16:45     ` Daniel Jordan
2018-11-20 16:33       ` Tejun Heo
2018-11-20 17:03         ` Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 06/13] vfio: parallelize vfio_pin_map_dma Daniel Jordan
2018-11-05 21:51   ` Alex Williamson
2018-11-06  2:42     ` Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 07/13] mm: change locked_vm's type from unsigned long to atomic_long_t Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 08/13] vfio: remove unnecessary mmap_sem writer acquisition around locked_vm Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 09/13] vfio: relieve mmap_sem reader cacheline bouncing by holding it longer Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 10/13] mm: enlarge type of offset argument in mem_map_offset and mem_map_next Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 11/13] mm: parallelize deferred struct page initialization within each node Daniel Jordan
2018-11-10  3:48   ` Elliott, Robert (Persistent Memory)
2018-11-12 16:54     ` Daniel Jordan
2018-11-12 22:15       ` Elliott, Robert (Persistent Memory)
2018-11-19 16:01         ` Daniel Jordan
2018-11-27  0:12           ` Elliott, Robert (Persistent Memory)
2018-11-27 20:23             ` Daniel Jordan [this message]
2018-11-19 16:29       ` Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 12/13] mm: parallelize clear_gigantic_page Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 13/13] hugetlbfs: parallelize hugetlbfs_fallocate with ktask Daniel Jordan
2018-11-05 17:29 ` [RFC PATCH v4 00/13] ktask: multithread CPU-intensive kernel work Michal Hocko
2018-11-06  1:29   ` Daniel Jordan
2018-11-06  9:21     ` Michal Hocko
2018-11-07 20:17       ` Daniel Jordan
2018-11-05 18:49 ` Zi Yan
2018-11-06  2:20   ` Daniel Jordan
2018-11-06  2:48     ` Zi Yan
2018-11-06 19:00       ` Daniel Jordan
2018-11-30 19:18 ` Tejun Heo
2018-12-01  0:13   ` Daniel Jordan
2018-12-03 16:16     ` Tejun Heo

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