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From: Nick Desaulniers <ndesaulniers@google.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Sami Tolvanen <samitolvanen@google.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Will Deacon <will@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	linux-arch <linux-arch@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	linux-pci <linux-pci@vger.kernel.org>
Subject: Re: [PATCH v8 00/16] Add support for Clang LTO
Date: Tue, 8 Dec 2020 13:09:54 -0800	[thread overview]
Message-ID: <CAKwvOd=hL=Vt1ATYqky9jmv+tM5hpTnLRuZudG-7ki0EYoFGJQ@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a1Xfpt7QLkvxjtXKcgzcWkS8g9bmxD687+rqjTafTzKrg@mail.gmail.com>

On Tue, Dec 8, 2020 at 1:00 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> On Tue, Dec 8, 2020 at 5:43 PM 'Sami Tolvanen' via Clang Built Linux
> <clang-built-linux@googlegroups.com> wrote:
> >
> > On Tue, Dec 8, 2020 at 4:15 AM Arnd Bergmann <arnd@kernel.org> wrote:
> > >
> > > - one build seems to take even longer to link. It's currently at 35GB RAM
> > >   usage and 40 minutes into the final link, but I'm worried it might
> > > not complete
> > >   before it runs out of memory.  I only have 128GB installed, and google-chrome
> > >   uses another 30GB of that, and I'm also doing some other builds in parallel.
> > >   Is there a minimum recommended amount of memory for doing LTO builds?
> >
> > When building arm64 defconfig, the maximum memory usage I measured
> > with ThinLTO was 3.5 GB, and with full LTO 20.3 GB. I haven't measured
> > larger configurations, but I believe LLD can easily consume 3-4x that
> > much with full LTO allyesconfig.
>
> Ok, that's not too bad then. Is there actually a reason to still
> support full-lto
> in your series? As I understand it, full LTO was the initial approach and
> used to work better, but thin LTO is actually what we want to use in the
> long run. Perhaps dropping the full LTO option from your series now
> that thin LTO works well enough and uses less resources would help
> avoid some of the problems.

While all developers agree that ThinLTO is a much more palatable
experience than full LTO; our product teams prefer the excessive build
time and memory high water mark (at build time) costs in exchange for
slightly better performance than ThinLTO in <benchmarks that I've been
told are important>.  Keeping support for full LTO in tree would help
our product teams reduce the amount of out of tree code they have.  As
long as <benchmarks that I've been told are important> help
sell/differentiate phones, I suspect our product teams will continue
to ship full LTO in production.
-- 
Thanks,
~Nick Desaulniers

WARNING: multiple messages have this Message-ID (diff)
From: Nick Desaulniers <ndesaulniers@google.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: linux-arch <linux-arch@vger.kernel.org>,
	Kees Cook <keescook@chromium.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	linux-pci <linux-pci@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Sami Tolvanen <samitolvanen@google.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Will Deacon <will@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v8 00/16] Add support for Clang LTO
Date: Tue, 8 Dec 2020 13:09:54 -0800	[thread overview]
Message-ID: <CAKwvOd=hL=Vt1ATYqky9jmv+tM5hpTnLRuZudG-7ki0EYoFGJQ@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a1Xfpt7QLkvxjtXKcgzcWkS8g9bmxD687+rqjTafTzKrg@mail.gmail.com>

On Tue, Dec 8, 2020 at 1:00 PM Arnd Bergmann <arnd@kernel.org> wrote:
>
> On Tue, Dec 8, 2020 at 5:43 PM 'Sami Tolvanen' via Clang Built Linux
> <clang-built-linux@googlegroups.com> wrote:
> >
> > On Tue, Dec 8, 2020 at 4:15 AM Arnd Bergmann <arnd@kernel.org> wrote:
> > >
> > > - one build seems to take even longer to link. It's currently at 35GB RAM
> > >   usage and 40 minutes into the final link, but I'm worried it might
> > > not complete
> > >   before it runs out of memory.  I only have 128GB installed, and google-chrome
> > >   uses another 30GB of that, and I'm also doing some other builds in parallel.
> > >   Is there a minimum recommended amount of memory for doing LTO builds?
> >
> > When building arm64 defconfig, the maximum memory usage I measured
> > with ThinLTO was 3.5 GB, and with full LTO 20.3 GB. I haven't measured
> > larger configurations, but I believe LLD can easily consume 3-4x that
> > much with full LTO allyesconfig.
>
> Ok, that's not too bad then. Is there actually a reason to still
> support full-lto
> in your series? As I understand it, full LTO was the initial approach and
> used to work better, but thin LTO is actually what we want to use in the
> long run. Perhaps dropping the full LTO option from your series now
> that thin LTO works well enough and uses less resources would help
> avoid some of the problems.

While all developers agree that ThinLTO is a much more palatable
experience than full LTO; our product teams prefer the excessive build
time and memory high water mark (at build time) costs in exchange for
slightly better performance than ThinLTO in <benchmarks that I've been
told are important>.  Keeping support for full LTO in tree would help
our product teams reduce the amount of out of tree code they have.  As
long as <benchmarks that I've been told are important> help
sell/differentiate phones, I suspect our product teams will continue
to ship full LTO in production.
-- 
Thanks,
~Nick Desaulniers

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2020-12-08 21:11 UTC|newest]

Thread overview: 141+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-01 21:36 [PATCH v8 00/16] Add support for Clang LTO Sami Tolvanen
2020-12-01 21:36 ` Sami Tolvanen
2020-12-01 21:36 ` Sami Tolvanen
2020-12-01 21:36 ` [PATCH v8 01/16] tracing: move function tracer options to Kconfig Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:47   ` Steven Rostedt
2020-12-01 21:47     ` Steven Rostedt
2020-12-01 21:36 ` [PATCH v8 02/16] kbuild: add support for Clang LTO Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-02  2:59   ` Masahiro Yamada
2020-12-02  2:59     ` Masahiro Yamada
2020-12-03  0:07   ` Nick Desaulniers
2020-12-03  0:07     ` Nick Desaulniers
2020-12-03  0:07     ` Nick Desaulniers
2020-12-01 21:36 ` [PATCH v8 03/16] kbuild: lto: fix module versioning Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:36 ` [PATCH v8 04/16] kbuild: lto: limit inlining Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:36 ` [PATCH v8 05/16] kbuild: lto: merge module sections Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:36 ` [PATCH v8 06/16] kbuild: lto: remove duplicate dependencies from .mod files Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:36 ` [PATCH v8 07/16] init: lto: ensure initcall ordering Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:36 ` [PATCH v8 08/16] init: lto: fix PREL32 relocations Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:36   ` Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 09/16] PCI: Fix PREL32 relocations for LTO Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 10/16] modpost: lto: strip .lto from module names Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 11/16] scripts/mod: disable LTO for empty.c Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 12/16] efi/libstub: disable LTO Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 13/16] drivers/misc/lkdtm: disable LTO for rodata.o Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 14/16] arm64: vdso: disable LTO Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 15/16] arm64: disable recordmcount with DYNAMIC_FTRACE_WITH_REGS Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 16/16] arm64: allow LTO to be selected Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-01 21:37   ` Sami Tolvanen
2020-12-03  0:01 ` [PATCH v8 00/16] Add support for Clang LTO Nick Desaulniers
2020-12-03  0:01   ` Nick Desaulniers
2020-12-03  0:01   ` Nick Desaulniers
2020-12-03 11:26 ` Will Deacon
2020-12-03 11:26   ` Will Deacon
2020-12-03 17:07   ` Sami Tolvanen
2020-12-03 17:07     ` Sami Tolvanen
2020-12-03 17:07     ` Sami Tolvanen
2020-12-03 18:21     ` Nathan Chancellor
2020-12-03 18:21       ` Nathan Chancellor
2020-12-03 18:22     ` Will Deacon
2020-12-03 18:22       ` Will Deacon
2020-12-03 22:32       ` Nick Desaulniers
2020-12-03 22:32         ` Nick Desaulniers
2020-12-03 22:32         ` Nick Desaulniers
2020-12-04  9:35         ` Will Deacon
2020-12-04  9:35           ` Will Deacon
2020-12-04 22:52         ` Sami Tolvanen
2020-12-04 22:52           ` Sami Tolvanen
2020-12-04 22:52           ` Sami Tolvanen
2020-12-06  6:50           ` Nathan Chancellor
2020-12-06  6:50             ` Nathan Chancellor
2020-12-06 20:09             ` Sami Tolvanen
2020-12-06 20:09               ` Sami Tolvanen
2020-12-06 20:09               ` Sami Tolvanen
2020-12-08  0:46               ` Nathan Chancellor
2020-12-08  0:46                 ` Nathan Chancellor
2020-12-08 12:15 ` Arnd Bergmann
2020-12-08 12:15   ` Arnd Bergmann
2020-12-08 12:15   ` Arnd Bergmann
2020-12-08 13:54   ` Arnd Bergmann
2020-12-08 13:54     ` Arnd Bergmann
2020-12-08 13:54     ` Arnd Bergmann
2020-12-08 16:53     ` Sami Tolvanen
2020-12-08 16:53       ` Sami Tolvanen
2020-12-08 16:53       ` Sami Tolvanen
2020-12-08 16:56       ` Arnd Bergmann
2020-12-08 16:56         ` Arnd Bergmann
2020-12-08 16:56         ` Arnd Bergmann
2020-12-08 16:43   ` Sami Tolvanen
2020-12-08 16:43     ` Sami Tolvanen
2020-12-08 16:43     ` Sami Tolvanen
2020-12-08 20:59     ` Arnd Bergmann
2020-12-08 20:59       ` Arnd Bergmann
2020-12-08 21:02       ` Arnd Bergmann
2020-12-08 21:02         ` Arnd Bergmann
2020-12-09  5:23         ` Fāng-ruì Sòng
2020-12-09  5:23           ` Fāng-ruì Sòng
2020-12-09  5:23           ` Fāng-ruì Sòng
2020-12-09  9:07           ` Arnd Bergmann
2020-12-09  9:07             ` Arnd Bergmann
2020-12-09  9:07             ` Arnd Bergmann
2020-12-09  9:59         ` Arnd Bergmann
2020-12-09  9:59           ` Arnd Bergmann
2020-12-09 16:09         ` Sami Tolvanen
2020-12-09 16:09           ` Sami Tolvanen
2020-12-09 16:09           ` Sami Tolvanen
2020-12-09 19:24           ` Arnd Bergmann
2020-12-09 19:24             ` Arnd Bergmann
2020-12-09 19:24             ` Arnd Bergmann
2020-12-08 21:09       ` Nick Desaulniers [this message]
2020-12-08 21:09         ` Nick Desaulniers
2020-12-08 21:09         ` Nick Desaulniers
2020-12-08 22:20         ` Arnd Bergmann
2020-12-08 22:20           ` Arnd Bergmann
2020-12-08 22:20           ` Arnd Bergmann
2020-12-09 16:11           ` Sami Tolvanen
2020-12-09 16:11             ` Sami Tolvanen
2020-12-09 16:11             ` Sami Tolvanen
2020-12-09  4:55     ` Fangrui Song
2020-12-09  4:55       ` Fangrui Song
2020-12-09  9:19       ` Arnd Bergmann
2020-12-09  9:19         ` Arnd Bergmann
2020-12-09  9:19         ` Arnd Bergmann
2020-12-09 12:35   ` Arnd Bergmann
2020-12-09 12:35     ` Arnd Bergmann
2020-12-09 12:35     ` Arnd Bergmann
2020-12-09 16:25     ` Sami Tolvanen
2020-12-09 16:25       ` Sami Tolvanen
2020-12-09 16:25       ` Sami Tolvanen
2020-12-09 17:51       ` Arnd Bergmann
2020-12-09 17:51         ` Arnd Bergmann
2020-12-09 17:51         ` Arnd Bergmann

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