Hi Tom, On Mon, 14 Mar 2022 at 06:49, Tom Rini <tr...@konsulko.com> wrote: > > On Sat, Mar 12, 2022 at 10:58:44AM -0700, Simon Glass wrote: > > Hi Tom, > > > > On Mon, 7 Mar 2022 at 07:33, Tom Rini <tr...@konsulko.com> wrote: > > > > > > On Fri, Mar 04, 2022 at 08:42:57AM -0700, Simon Glass wrote: > > > > > > > LTO (Link-Time Optimisation) is an very useful feature which can > > > > significantly reduce the size of U-Boot binaries. So far it has been > > > > made available for selected ARM boards and sandbox. > > > > > > > > However, incremental builds are much slower when LTO is used. For > > > > example, > > > > an incremental build of sandbox takes 2.1 seconds on my machine, but 6.7 > > > > seconds with LTO enabled. > > > > > > > > Add a LTO_BUILD=n parameter to the build, so it can be disabled during > > > > development if needed, for faster builds. > > > > > > > > Add some documentation about LTO while we are here. > > > > > > > > Signed-off-by: Simon Glass <s...@chromium.org> > > > > > > We don't need this since you can do: > > > make EXTRA_CFLAGS="-fno-lto" EXTRA_LDFLAGS="-fno-lto" > > > to pass -fno-lto to compile/linking and disable lto and per > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46905 this has been working > > > for some time. > > > > Thanks for that, it is a big pain point for me, picking up this patch > > for every series I write. The incremental build time for sandbox goes > > from 3 seconds to 27 seconds on my laptop with LTO, which is > > intolerable. > > Yeah, I noticed it's visible on my laptop, but not at all on my desktop > (i7 vs Ryzen 7). > > > The EXTRA_CFLAGS says it is for 'Backward compatibility' and it still > > does the various LTO things (i.e. it changes the build logic). It > > We're unlikely to move to newer Linux kernel kbuild logic so this isn't > going away, and there's not much in the way of logic that's changed for > LTO that I see. > > > seems odd to me to enable the option and then disable it later in the > > command line. It is therefore not quite equivalent. But it seems to > > work well enough for me fom a small amount of testing. If you are > > really set on not having a special option for it, I can live with it > > for now. I'm also not convinced that my patch entirely removes the LTO > > stuff in a consistent way. > > Yeah, I really don't want to go down the path of overriding CONFIG > options via make/environment logic. I'm also open to turning off LTO on > sandbox and on with qemu-* so it gets wider CI testing.
Yes you did mention that, but the problem is that LTO is very handy with sandbox, to test the strange things that happen. For example, I found the bug where LTO was dropping a linker-list item, using sandbox. We could perhaps make one of the sandbox builds not use LTO, e.g. sandbox_flattree ? Regards, Simon
