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From: "Du, Changbin" <changbin.du@intel.com>
To: Daniel Thompson <daniel.thompson@linaro.org>
Cc: changbin.du@intel.com, yamada.masahiro@socionext.com,
	michal.lkml@markovi.net, tglx@linutronix.de, mingo@redhat.com,
	akpm@linux-foundation.org, rostedt@goodmis.org,
	rdunlap@infradead.org, x86@kernel.org, lgirdwood@gmail.com,
	broonie@kernel.org, arnd@arndb.de, linux-kbuild@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: [PATCH v2 0/5] kernel hacking: GCC optimization for debug experience (-Og)
Date: Thu, 3 May 2018 21:49:26 +0800	[thread overview]
Message-ID: <20180503134925.eyqna4ydogtkmvph@intel.com> (raw)
In-Reply-To: <20180502145631.bzfqpw4izlrqhda6@holly.lan>

On Wed, May 02, 2018 at 03:56:31PM +0100, Daniel Thompson wrote:
> On Wed, May 02, 2018 at 09:44:55PM +0800, changbin.du@intel.com wrote:
> > From: Changbin Du <changbin.du@intel.com>
> > 
> > Hi all,
> > I know some kernel developers was searching for a method to dissable GCC
> > optimizations, probably they want to apply GCC '-O0' option. But since Linux
> > kernel replys on GCC optimization to remove some dead code, so '-O0' just
> > breaks the build. They do need this because they want to debug kernel with
> > qemu, simics, kgtp or kgdb.
> > 
> > Thanks for the GCC '-Og' optimization level introduced in GCC 4.8, which
> > offers a reasonable level of optimization while maintaining fast compilation
> > and a good debugging experience. It is similar to '-O1' while perfer keeping
> > debug ability over runtime speed. With '-Og', we can build a kernel with
> > better debug ability and little performance drop after some simple change.
> > 
> > In this series, firstly introduce a new config CONFIG_NO_AUTO_INLINE after two
> > fixes for this new option. With this option, only functions explicitly marked
> > with "inline" will  be inlined. This will allow the function tracer to trace
> > more functions because it only traces functions that the compiler has not
> > inlined.
> > 
> > Then introduce new config CONFIG_DEBUG_EXPERIENCE which apply '-Og'
> > optimization level for whole kernel, with a simple fix in fix_to_virt().
> > Currently this option is only tested on a QEMU gust and it works fine.
> > 
> > 
> > Comparison of vmlinux size: a bit smaller.
> > 
> >     w/o CONFIG_DEBUG_EXPERIENCE
> >     $ size vmlinux
> >        text    data     bss     dec     hex filename
> >     22665554   9709674  2920908 35296136        21a9388 vmlinux
> > 
> >     w/ CONFIG_DEBUG_EXPERIENCE
> >     $ size vmlinux
> >        text    data     bss     dec     hex filename
> >     21499032   10102758 2920908 34522698        20ec64a vmlinux
> > 
> > 
> > Comparison of system performance: a bit drop (~6%).
> >     This benchmark of kernel compilation is suggested by Ingo Molnar.
> >     https://lkml.org/lkml/2018/5/2/74
> 
> In my mind was the opposite question. When running on the same kernel
> does a kernel whose config contains CONFIG_DEBUG_EXPERIENCE build faster
> than one without (due to the disabled optimization passes).
> 
> To be honest this is more curiosity than a review comment though... if
> you have the figures please share, if not then don't sweat it on my
> account!
> 
> 
> Daniel.
>
Sorry I don't have the data yet. Per the comment in GCC, I think it should be a
little faster but not obviously.

> 
-- 
Thanks,
Changbin Du

      reply	other threads:[~2018-05-03 13:59 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-02 13:44 changbin.du
2018-05-02 13:44 ` [PATCH v2 1/5] x86/mm: surround level4_kernel_pgt with #ifdef CONFIG_X86_5LEVEL...#endif changbin.du
2018-05-02 13:44 ` [PATCH v2 2/5] regulator: add dummy function of_find_regulator_by_node changbin.du
2018-05-02 13:44 ` [PATCH v2 3/5] kernel hacking: new config NO_AUTO_INLINE to disable compiler auto-inline optimizations changbin.du
2018-05-02 14:07   ` Steven Rostedt
2018-05-02 20:27   ` Arnd Bergmann
2018-05-03 13:00     ` Du, Changbin
2018-05-03 14:16       ` Steven Rostedt
2018-05-02 13:44 ` [PATCH v2 4/5] kernel hacking: new config DEBUG_EXPERIENCE to apply GCC -Og optimization changbin.du
2018-05-02 14:17   ` Steven Rostedt
2018-05-02 20:45     ` Andrew Morton
2018-05-03  1:19       ` Steven Rostedt
2018-05-03 13:45         ` Du, Changbin
2018-05-03 14:28           ` Steven Rostedt
2018-05-05 23:57             ` Du, Changbin
2018-05-06  0:27               ` Randy Dunlap
2018-05-02 19:26   ` Randy Dunlap
2018-05-02 13:45 ` [PATCH v2 5/5] asm-generic: fix build error in fix_to_virt with CONFIG_DEBUG_EXPERIENCE changbin.du
2018-05-02 14:19   ` Steven Rostedt
2018-05-03 13:25     ` Du, Changbin
2018-05-03 14:19       ` Steven Rostedt
2018-05-03 16:39         ` weylin
2018-05-02 14:56 ` [PATCH v2 0/5] kernel hacking: GCC optimization for debug experience (-Og) Daniel Thompson
2018-05-03 13:49   ` Du, Changbin [this message]

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