linux-kernel - RE: [GIT PULL] pin control bulk changes for v4.16

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Date:   Mon, 5 Feb 2018 10:09:36 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>
CC:     linux-kernel <linux-kernel@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: RE: [GIT PULL] pin control bulk changes for v4.16

From: Linus Torvalds
> Sent: 02 February 2018 22:57
...
> I also wonder if there are any automated tools that try to find these
> kinds of crazy things. I suspect a lot of our build times is the poor
> compiler just reading and parsing header files over and over again,
> and a lot of them are probably not needed.

I've counted system calls during a NetBSD kernel build, I imagine Linux is
much the same.
Most of the calls were open(), and most of those failing opens.
I suspected that most came from searching the -I path to find headers.
Build over NFS and the cost is even more significant (every directory
name in the path (used to) require an NFS message exchange).

	David