linux-kernel - Re: [4.9-rc1] Build-time 2x slower

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Date:   Tue, 18 Oct 2016 18:49:24 +0200
From:   Jörg Otte <jrg.otte@...il.com>
To:     sedat.dilek@...il.com
Cc:     Ming Lei <tom.leiming@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [4.9-rc1] Build-time 2x slower

2016-10-18 11:30 GMT+02:00 Sedat Dilek <sedat.dilek@...il.com>:
> On Tue, Oct 18, 2016 at 3:38 AM, Ming Lei <tom.leiming@...il.com> wrote:
>> On Tue, Oct 18, 2016 at 12:04 AM, Sedat Dilek <sedat.dilek@...il.com> wrote:
>>> Hi Linus,
>>>
>>> not sure whom to address on this issue.
>>>
>>> I have built Linux v4.9-rc1, v4.8.2 and v4.4.25 kernels (in this
>>> order) this morning.
>>>
>>> Building a Linux v4.8.2 under Linux v4.9-rc1 took two times longer.
>>>
>>> As usually I build with 2 parallel-make-jobs.
>>> This takes approx. 30mins.
>>> Under Linux v4.9-rc1 it took approx. an hour.
>>>
>>> My system is a Ubuntu/precise AMD64 (WUBI installation).
>>> I use my normal build-environment.
>>>
>>> If you need further informations, please let me know.
>>
>> Kernel building is more like a CPU-bound workload, so maybe
>> some clues can be got by comparing results of 'perf top/record',
>> which should be very easy to collect.
>>
>
> I have no big experiences with perf.
> Last I played was testing early days of "lockdep" feature.
> Can you give some clear instructions on how to use perf top/record in
> this scenario?
>
> - Sedat -
>
>>>
>>> Regards,
>>> - Sedat -
>>>
>>> P.S.: Listing content of attached tarball file.
>>>
>>> $ LC_ALL=C ls -R
>>> .:
>>> build-time  configs  scripts  toolchain-amd64
>>>
>>> ./build-time:
>>> ls-alt_building-4-4-25-under-4-8-2.txt
>>> ls-alt_building-4-8-2-under-4-9-0-rc1.txt
>>>
>>> ./configs:
>>> WHATS-IN-DILEKS-LINUX-KERNEL.txt  config-4.4.25-1-iniza-small
>>> config-4.8.2-1-iniza-small  config-4.9.0-rc1-1-iniza-small
>>>
>>> ./scripts:
>>> build_linux-upstream.sh
>>>
>>> ./toolchain-amd64:
>>> HOST-AND-BUILD-TOOLCHAIN.txt
>>
>>
>>
>> Thanks,
>> Ming Lei

I can confirm the problem. I use 3 build jobs in parallel
and the kernel build takes 2,5 times longer.

I'm only seeing 1 (of 4) cores are running with max frequency.
The other are running in minimum frequency. And this seems not
to be limited to build jobs however.

The last known good kernel for me is  ..-4.8.0-14604-g29fbff8

Jörg