On 01/19/22 at 07:44pm, Jisheng Zhang wrote: > On Wed, Jan 19, 2022 at 05:33:22PM +0800, Baoquan He wrote: > > On 01/19/22 at 09:52am, Alexandre Ghiti wrote: > > > Hi Baoquan, > > > > > > On Wed, Jan 19, 2022 at 9:11 AM Baoquan He <bhe@xxxxxxxxxx> wrote: > > > > > > > > On 01/18/22 at 10:13pm, Jisheng Zhang wrote: > > > > > On Sun, Jan 16, 2022 at 09:38:47PM +0800, Baoquan He wrote: > > > > > > Hi Jisheng, > > > > > > > > > > Hi Baoquan, > > > > > > > > > > > > > > > > > On 12/07/21 at 12:05am, Jisheng Zhang wrote: > > > > > > > Replace the conditional compilation using "#ifdef CONFIG_KEXEC_CORE" > > > > > > > by a check for "IS_ENABLED(CONFIG_KEXEC_CORE)", to simplify the code > > > > > > > and increase compile coverage. > > > > > > > > > > > > I go through this patchset, You mention the benefits it brings are > > > > > > 1) simplity the code; > > > > > > 2) increase compile coverage; > > > > > > > > > > > > For benefit 1), it mainly removes the dummy function in x86, arm and > > > > > > arm64, right? > > > > > > > > > > Another benefit: remove those #ifdef #else #endif usage. Recently, I > > > > > fixed a bug due to lots of "#ifdefs": > > > > > http://lists.infradead.org/pipermail/linux-riscv/2021-December/010607.html > > > > > > > > Glad to know the fix. While, sometime the ifdeffery is necessary. I am > > > > sorry about the one in riscv and you have fixed, it's truly a bug . But, > > > > the increasing compile coverage at below you tried to make, it may cause > > > > issue. Please see below my comment. > > > > > > > > > > > > > > > > > > > > > For benefit 2), increasing compile coverage, could you tell more how it > > > > > > achieves and why it matters? What if people disables CONFIG_KEXEC_CORE in > > > > > > purpose? Please forgive my poor compiling knowledge. > > > > > > > > > > Just my humble opinion, let's compare the code:: > > > > > > > > > > #ifdef CONFIG_KEXEC_CORE > > > > > > > > > > code block A; > > > > > > > > > > #endif > > > > > > > > > > If KEXEC_CORE is disabled, code block A won't be compiled at all, the > > > > > preprocessor will remove code block A; > > > > > > > > > > If we convert the code to: > > > > > > > > > > if (IS_ENABLED(CONFIG_KEXEC_CORE)) { > > > > > code block A; > > > > > } > > > > > > > > > > Even if KEXEC_CORE is disabled, code block A is still compiled. > > > > > > > > This is what I am worried about. Before, if CONFIG_KEXEC_CORE is > > > > unset, those relevant codes are not compiled in. I can't see what > > > > benefit is brought in if compiled in the unneeded code block. Do I miss > > > > anything? > > > > > > > > > > This is explained in Documentation/process/coding-style.rst "21) > > > Conditional Compilation". > > > > Thanks for the pointer, Alex. > > > > I read that part, while my confusion isn't gone. With the current code, > > CONFIG_KEXEC_CORE is set, > > - reserve_crashkernel_low() and reserve_crashkernel() compiled in. > > Although the code block will be compiled, but the code block will be > optimized out. > > > CONFIG_KEXEC_CORE is unset, > > - reserve_crashkernel_low() and reserve_crashkernel() compiled out. > > > > After this patch applied, does it have the same effect as the old code? > > I compared the .o, and can confirm they acchieve the same effect. Checked the .o, it's truly as you said. I didn't know this before, thank you and Alex, learned this now. Seems only static function has this effect. I tested your x86 patch, those two functions are all optimized out. If I remove the static, the entire reserve_crashkernel_low() exists, while reserve_crashkernel() will be optimized as a empty function. _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
