Messages in this thread | | | From | Arnd Bergmann <> | Date | Tue, 26 May 2020 14:19:18 +0200 | Subject | Re: [PATCH -tip v3 09/11] data_race: Avoid nested statement expression |
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On Tue, May 26, 2020 at 2:02 PM Will Deacon <will@kernel.org> wrote: > On Tue, May 26, 2020 at 12:42:16PM +0200, Arnd Bergmann wrote: > > > > I find this patch only solves half the problem: it's much faster than > > without the > > patch, but still much slower than the current mainline version. As far as I'm > > concerned, I think the build speed regression compared to mainline is not yet > > acceptable, and we should try harder. > > > > I have not looked too deeply at it yet, but this is what I found from looking > > at a file in a randconfig build: > > > > Configuration: see https://pastebin.com/raw/R9erCwNj > > So this .config actually has KCSAN enabled. Do you still see the slowdown > with that disabled?
Yes, enabling or disabling KCSAN seems to make no difference to compile speed in this config and source file, I still get the 12 seconds preprocessing time and 9MB file size with KCSAN disabled, possibly a few percent smaller/faster. I actually thought that CONFIG_FTRACE had a bigger impact, but disabling that also just reduces the time by a few percent rather than getting it down to the expected milliseconds.
> Although not ideal, having a longer compiler time when > the compiler is being asked to perform instrumentation doesn't seem like a > show-stopper to me.
I agree in general, but building an allyesconfig kernel is still an important use case that should not take twice as long after a small kernel change regardless of whether a new feature is used or not. (I have not actually compared the overall build speed for allmodconfig, as this takes a really long time at the moment)
Arnd
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