linux-kernel - Re: Compiling kernels faster (was Re: v4.10: kernel stack frame pointer .. has bad value (null))

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Message-ID: <CAMuHMdX6yQsdTrp8bE4LkaFZKbwFadrHXS80_O1VsW_z+hBw2A@mail.gmail.com>
Date:   Fri, 10 Mar 2017 14:28:21 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Pavel Machek <pavel@....cz>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andy Lutomirski <luto@...capital.net>,
        kernel list <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Peter Anvin <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Compiling kernels faster (was Re: v4.10: kernel stack frame
 pointer .. has bad value (null))

Hi Pavel,

On Fri, Mar 10, 2017 at 2:17 PM, Pavel Machek <pavel@....cz> wrote:
> On Thu 2017-03-09 13:16:09, Geert Uytterhoeven wrote:
>> On Thu, Mar 9, 2017 at 11:56 AM, Pavel Machek <pavel@....cz> wrote:
>> > On Thu 2017-03-09 10:38:46, Geert Uytterhoeven wrote:
>> >> I hope you do use ccache or distcc?
>> >
>> > I tried to use distcc before, but it was rather hard to maintain. No
>> > ccache here. Hmm. I guess ccache really makes sense for bisect.
>>
>> Yes it does. So if you're not using it yet, do the below, today, not tomorrow.
>>
>> If your distro supports it, prepend /usr/lib/ccache/ to your $PATH.
>> Create symlinks from the names of your favorite cross-compilers
>> to /usr/bin/ccache, and make sure they are early in your $PATH.
>>
>> That's it! Enjoy!
>
> Hmm. Installed, and seems to work. OTOH, compilation now seems to
> produce 2-3MB/sec writing on spinning rust, and CPUs are no longer
> fully loaded. (make -j 7 on 2 core HT machine). Any io load sends the
> CPU utilization to cca 50% range... Compilation goes up from 9:13 to
> 11:40... to 23 minutes depending on situation. I guess it is still

I guess that was the first build, with a clean cache?
Now run "make clean", and try again ;-)

BTW, I tend not to do -j beyond the number of cores/threads (i.e. -j 8
on the i7-4770), unless you just want to compile, and not enjoy other
interactive work ;-)

> worth it for the bisect, but it looks like ccache really needs an ssd.

Adding an SSD never hurts.
Although I have been a happy user of ccache since long before I got an SSD.

> Hmm. And killing chromium matters a lot for a compile time. I hate
> modern web :-(.

Adding (freeing) RAM also never hurts ;-)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds