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From: Dave Hansen <dave.hansen@intel.com>
To: Wei Yang <richard.weiyang@gmail.com>
Cc: akpm@linux-foundation.org, mhocko@suse.com, rientjes@google.com,
	linux-mm@kvack.org, kirill.shutemov@linux.intel.com
Subject: Re: [PATCH 1/3] mm/sparse: add likely to mem_section[root] check in sparse_index_init()
Date: Mon, 10 Sep 2018 13:30:11 -0700	[thread overview]
Message-ID: <5140697b-540a-1db1-e300-af1aaece97ad@intel.com> (raw)
In-Reply-To: <20180909013807.6ux4cidt3nehofz5@master>

On 09/08/2018 06:38 PM, owner-linux-mm@kvack.org wrote:
> 
> At last, here is the test result on my 4G virtual machine. I added printk
> before and after sparse_memory_present_with_active_regions() and tested three
> times with/without "likely".
> 
>                without      with
>     Elapsed   0.000252     0.000250   -0.8%
> 
> The benefit seems to be too small on a 4G virtual machine or even this is not
> stable. Not sure we can see some visible effect on a 32G machine.

I think it's highly unlikely you have found something significant here.
It's one system, in a VM and it's not being measured using a mechanism
that is suitable for benchmarking (the kernel dmesg timestamps).

Plus, if this is a really tight loop, the cpu's branch predictors will
be good at it.

  reply	other threads:[~2018-09-10 20:31 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-23 13:07 [PATCH 0/3] trivial code refine for sparsemem Wei Yang
2018-08-23 13:07 ` [PATCH 1/3] mm/sparse: add likely to mem_section[root] check in sparse_index_init() Wei Yang
2018-08-23 13:13   ` Michal Hocko
2018-08-23 22:57     ` Wei Yang
2018-08-24  7:31       ` Michal Hocko
2018-08-24  0:11   ` Dave Hansen
2018-08-24 15:07     ` Wei Yang
2018-09-03 22:27       ` Wei Yang
2018-09-09  1:38         ` Wei Yang
2018-09-10 20:30           ` Dave Hansen [this message]
2018-09-11 15:00             ` Wei Yang
2018-08-23 13:07 ` [PATCH 2/3] mm/sparse: expand the CONFIG_SPARSEMEM_EXTREME range in __nr_to_section() Wei Yang
2018-08-23 13:21   ` Michal Hocko
2018-08-23 23:03     ` Wei Yang
2018-08-24  0:09     ` Dave Hansen
2018-08-24 15:24       ` Wei Yang
2018-08-23 13:07 ` [PATCH 3/3] mm/sparse: use __highest_present_section_nr as the boundary for pfn check Wei Yang
2018-08-23 13:25   ` Michal Hocko
2018-08-23 14:00     ` Oscar Salvador
2018-08-23 19:17       ` Michal Hocko
2018-08-23 20:52         ` Oscar Salvador
2018-08-24  0:15   ` Dave Hansen
2018-08-24 18:11     ` Wei Yang

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