From: Wei Yang <richard.weiyang@gmail.com>
To: Tejun Heo <tj@kernel.org>
Cc: Wei Yang <richard.weiyang@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 2/2] mm/sparse: add last_section_nr in sparse_init() to reduce some iteration cycle
Date: Wed, 8 Mar 2017 16:00:42 +0800 [thread overview]
Message-ID: <20170308080042.GA18355@WeideMacBook-Pro.local> (raw)
In-Reply-To: <20170306194225.GB19696@htj.duckdns.org>
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On Mon, Mar 06, 2017 at 02:42:25PM -0500, Tejun Heo wrote:
>Hello, Wei.
>
>On Fri, Feb 17, 2017 at 10:12:31PM +0800, Wei Yang wrote:
>> > And compare the ruling with the iteration for the loop to be (1UL <<
>> > 5) and (1UL << 19).
>> > The runtime is 0.00s and 0.04s respectively. The absolute value is not much.
>
>systemd-analyze usually does a pretty good job of breaking down which
>phase took how long. It might be worthwhile to test whether the
>improvement is actually visible during the boot.
>
Hi, Tejun
Thanks for your suggestion. I have tried systemd-analyze to measure the
effect, while looks not good.
Result without patch
-------------------------
Startup finished in 7.243s (kernel) + 25.034s (userspace) = 32.277s
Startup finished in 7.254s (kernel) + 19.816s (userspace) = 27.071s
Startup finished in 7.272s (kernel) + 4.363s (userspace) = 11.636s
Startup finished in 7.258s (kernel) + 24.319s (userspace) = 31.577s
Startup finished in 7.262s (kernel) + 9.481s (userspace) = 16.743s
Startup finished in 7.266s (kernel) + 14.766s (userspace) = 22.032s
Avg = 7.259s
Result with patch
-------------------------
Startup finished in 7.262s (kernel) + 14.294s (userspace) = 21.557s
Startup finished in 7.264s (kernel) + 19.519s (userspace) = 26.783s
Startup finished in 7.266s (kernel) + 4.730s (userspace) = 11.997s
Startup finished in 7.258s (kernel) + 9.514s (userspace) = 16.773s
Startup finished in 7.258s (kernel) + 14.371s (userspace) = 21.629s
Startup finished in 7.258s (kernel) + 14.627s (userspace) = 21.885s
Avg = 7.261s
It looks the effect is not obvious. Maybe the improvement is not good
enough :(
>> >> * Do we really need to add full reverse iterator to just get the
>> >> highest section number?
>> >>
>> >
>> > You are right. After I sent out the mail, I realized just highest pfn
>> > is necessary.
>
>That said, getting efficient is always great as long as the added
>complexity is justifiably small enough. If you can make the change
>simple enough, it'd be a lot easier to merge.
>
Agree.
I have replaced the reverse iteration with a simple last pfn return. The test
result above is based on the new version.
>Thanks.
>
>--
>tejun
--
Wei Yang
Help you, Help me
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prev parent reply other threads:[~2017-03-08 8:00 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-11 2:18 [RFC PATCH 1/2] mm/memblock: introduce for_each_mem_pfn_range_rev() Wei Yang
2017-02-11 2:18 ` [RFC PATCH 2/2] mm/sparse: add last_section_nr in sparse_init() to reduce some iteration cycle Wei Yang
2017-02-11 2:24 ` Tejun Heo
2017-02-13 13:03 ` Wei Yang
2017-02-17 14:12 ` Wei Yang
2017-03-06 19:42 ` Tejun Heo
2017-03-08 8:00 ` Wei Yang [this message]
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