On Thu, 2014-08-21 at 13:24 -0700, Dave Hansen wrote: > From: Dave Hansen <[email protected]> > > Changes from v2: > * remove tainting and stack track > * add debugfs file > * added a little text to guide folks who want to add more > options > > Changes from v1: > * remove schedstats > * add DEBUG_PAGEALLOC and SLUB_DEBUG_ON > > -- > > I have more than once myself been the victim of an accidentally- > enabled kernel config option being mistaken for a true > performance problem. > > I'm sure I've also taken profiles or performance measurements > and assumed they were real-world when really I was measuing the > performance with an option that nobody turns on in production. > > A warning like this late in boot will help remind folks when > these kinds of things are enabled. We can also teach tooling to > look for and capture /sys/kernel/debug/config_debug . > > As for the patch... > > I originally wanted this for CONFIG_DEBUG_VM, but I think it also > applies to things like lockdep and slab debugging. See the patch > for the list of offending config options. I'm open to adding > more, but this seemed like a good list to start. > > The compiler is smart enough to really trim down the code when > the array is empty. An objdump -d looks like this: > > lib/perf-configs.o: file format elf64-x86-64 > > Disassembly of section .init.text: > > 0000000000000000 <performance_taint>: > 0: 55 push %rbp > 1: 31 c0 xor %eax,%eax > 3: 48 89 e5 mov %rsp,%rbp > 6: 5d pop %rbp > 7: c3 retq > > This could be done with Kconfig and an #ifdef to save us 8 bytes > of text and the entry in the late_initcall() section. Doing it > this way lets us keep the list of these things in one spot, and > also gives us a convenient way to dump out the name of the > offending option. > > For anybody that *really* cares, I put the whole thing under > CONFIG_DEBUG_KERNEL in the Makefile. > > The messages look like this: > > [ 3.865297] WARNING: Do not use this kernel for performance measurement. > [ 3.868776] WARNING: Potentially performance-altering options: > [ 3.871558] CONFIG_LOCKDEP enabled > [ 3.873326] CONFIG_SLUB_DEBUG_ON enabled > > Signed-off-by: Dave Hansen <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: [email protected] > Cc: [email protected] > Cc: Andrew Morton <[email protected]> > Cc: Christoph Lameter <[email protected]> > Cc: Pekka Enberg <[email protected]> > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > --- > > b/include/linux/kernel.h | 1 > b/kernel/panic.c | 1 > b/lib/Makefile | 1 > b/lib/perf-configs.c | 114 > +++++++++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 117 insertions(+) > > diff -puN include/linux/kernel.h~taint-performance include/linux/kernel.h > --- a/include/linux/kernel.h~taint-performance 2014-08-19 > 11:38:07.424005355 -0700 > +++ b/include/linux/kernel.h 2014-08-19 11:38:20.960615904 -0700 > @@ -471,6 +471,7 @@ extern enum system_states { > #define TAINT_OOT_MODULE 12 > #define TAINT_UNSIGNED_MODULE 13 > #define TAINT_SOFTLOCKUP 14 > +#define TAINT_PERFORMANCE 15 > > extern const char hex_asc[]; > #define hex_asc_lo(x) hex_asc[((x) & 0x0f)] > diff -puN kernel/panic.c~taint-performance kernel/panic.c > --- a/kernel/panic.c~taint-performance 2014-08-19 11:38:28.928975233 > -0700 > +++ b/kernel/panic.c 2014-08-20 09:56:29.528471033 -0700 > @@ -225,6 +225,7 @@ static const struct tnt tnts[] = { > { TAINT_OOT_MODULE, 'O', ' ' }, > { TAINT_UNSIGNED_MODULE, 'E', ' ' }, > { TAINT_SOFTLOCKUP, 'L', ' ' }, > + { TAINT_PERFORMANCE, 'Q', ' ' }, > }; > > /** > diff -puN /dev/null lib/perf-configs.c > --- /dev/null 2014-04-10 11:28:14.066815724 -0700 > +++ b/lib/perf-configs.c 2014-08-21 13:22:25.586598278 -0700 > @@ -0,0 +1,114 @@ > +#include <linux/bug.h> > +#include <linux/debugfs.h> > +#include <linux/gfp.h> > +#include <linux/kernel.h> > +#include <linux/slab.h> > + > +/* > + * This should list any kernel options that can substantially > + * affect performance. This is intended to give a loud > + * warning during bootup so that folks have a fighting chance > + * of noticing these things. > + * > + * This is fairly subjective, but a good rule of thumb for these > + * is: if it is enabled widely in production, then it does not > + * belong here. If a major enterprise kernel enables a feature > + * for a non-debug kernel, it _really_ does not belong. > + */ > +static const char * const perfomance_killing_configs[] = { > +#ifdef CONFIG_LOCKDEP > + "LOCKDEP", > +#endif > +#ifdef CONFIG_LOCK_STAT > + "LOCK_STAT", > +#endif > +#ifdef CONFIG_DEBUG_VM > + "DEBUG_VM", > +#endif > +#ifdef CONFIG_DEBUG_VM_VMACACHE > + "DEBUG_VM_VMACACHE", > +#endif > +#ifdef CONFIG_DEBUG_VM_RB > + "DEBUG_VM_RB", > +#endif > +#ifdef CONFIG_DEBUG_SLAB > + "DEBUG_SLAB", > +#endif > +#ifdef CONFIG_SLUB_DEBUG_ON > + "SLUB_DEBUG_ON", > +#endif > +#ifdef CONFIG_DEBUG_OBJECTS_FREE > + "DEBUG_OBJECTS_FREE", > +#endif > +#ifdef CONFIG_DEBUG_KMEMLEAK > + "DEBUG_KMEMLEAK", > +#endif > +#ifdef CONFIG_DEBUG_PAGEALLOC > + "DEBUG_PAGEALLOC",
I think coverage profiling also impact performance. So I sould also put CONFIG_GCOV_KERNEL in the list. Tim
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