Messages in this thread | | | Date | Mon, 25 Apr 2022 16:01:26 +0800 | From | Feng Tang <> | Subject | Re: [PATCH v2] x86, vmlinux.lds: Add debug option to force all data sections aligned |
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Hi Peter,
On Mon, Apr 25, 2022 at 09:53:35AM +0200, Peter Zijlstra wrote: > On Sun, Apr 24, 2022 at 08:25:33PM +0800, Feng Tang wrote: > > > diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug > > index d3a6f74a94bd..7b8cfe9717f2 100644 > > --- a/arch/x86/Kconfig.debug > > +++ b/arch/x86/Kconfig.debug > > @@ -225,6 +225,19 @@ config PUNIT_ATOM_DEBUG > > The current power state can be read from > > /sys/kernel/debug/punit_atom/dev_power_state > > > > +config DEBUG_FORCE_DATA_SECTION_ALIGNED > > + bool "Force all data sections to be THREAD_SIZE aligned" > > s/THREAD_SIZE/PAGE_SIZE/ as that seems to be what the actual patch does.
Thanks for the catch! It was changed from v1 to v2, I should reviewed these texts more carefully, and there is another similar typo in the commit log.
> > + depends on EXPERT && !DYNAMIC_DEBUG > > + help > > + There are cases that a commit from one kernel domain changes > > + data sections' alignment of other domains, as they are all > > + linked together compactly, and cause magic performance bump > > + (regression or improvement), which is hard to debug. Enable > > + this option will help to verify if the bump is caused by > > + data alignment changes. > > + > > + It is mainly for debug and performance tuning use. > > + > > choice > > prompt "Choose kernel unwinder" > > default UNWINDER_ORC if X86_64 > > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S > > index 7fda7f27e762..6add703de45f 100644 > > --- a/arch/x86/kernel/vmlinux.lds.S > > +++ b/arch/x86/kernel/vmlinux.lds.S > > @@ -155,7 +155,17 @@ SECTIONS > > X86_ALIGN_RODATA_END > > > > /* Data */ > > - .data : AT(ADDR(.data) - LOAD_OFFSET) { > > + .data : AT(ADDR(.data) - LOAD_OFFSET) > > +#ifdef CONFIG_DEBUG_FORCE_DATA_SECTION_ALIGNED > > + /* > > + * In theroy, THREAD_SIZE as the biggest alignment of below sections > > I think the more common spelling is: 'theory' :-)
Yes, will change in the next verson.
Thanks, Feng
> > + * should be picked, but since upper 'X86_ALIGN_RODATA_END' can > > + * ganrantees the alignment of 'INIT_TASK_DATA', PAGE_SIZE is picked > > + * instead to reduce size of kernel binary > > + */ > > + SUBALIGN(PAGE_SIZE) > > +#endif > > + { > > /* Start of data section */ > > _sdata = .; > > > > -- > > 2.27.0 > >
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