From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
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.
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.
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.
The dump_stack() is really just to be loud.
For anybody that *really* cares, I put the whole thing under
#ifdef CONFIG_DEBUG_KERNEL.
The messages look like this:
[ 2.534574] CONFIG_LOCKDEP enabled
[ 2.536392] Do not use this kernel for performance measurement.
[ 2.547189] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.16.0-10473-gc8d6637-dirty #800
[ 2.558075] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
[ 2.564483] 0000000080000000 ffff88009c70be78 ffffffff817ce318 0000000000000000
[ 2.582505] ffffffff81dca5b6 ffff88009c70be88 ffffffff81dca5e2 ffff88009c70bef8
[ 2.588589] ffffffff81000377 0000000000000000 0007000700000142 ffffffff81b78968
[ 2.592638] Call Trace:
[ 2.593762] [<ffffffff817ce318>] dump_stack+0x4e/0x68
[ 2.597742] [<ffffffff81dca5b6>] ? oops_setup+0x2e/0x2e
[ 2.601247] [<ffffffff81dca5e2>] performance_taint+0x2c/0x3c
[ 2.603498] [<ffffffff81000377>] do_one_initcall+0xe7/0x290
[ 2.606556] [<ffffffff81db3215>] kernel_init_freeable+0x106/0x19a
[ 2.609718] [<ffffffff81db29e8>] ? do_early_param+0x86/0x86
[ 2.613772] [<ffffffff817bcfc0>] ? rest_init+0x150/0x150
[ 2.617333] [<ffffffff817bcfce>] kernel_init+0xe/0xf0
[ 2.620840] [<ffffffff817dbc7c>] ret_from_fork+0x7c/0xb0
[ 2.624718] [<ffffffff817bcfc0>] ? rest_init+0x150/0x150
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: ak@xxxxxxxxxxxxxxx
Cc: tim.c.chen@xxxxxxxxxxxxxxx
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
---
b/include/linux/kernel.h | 1 +
b/kernel/panic.c | 40 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 41 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 2014-08-19 14:14:23.444983711 -0700
@@ -225,6 +225,7 @@ static const struct tnt tnts[] = {
{ TAINT_OOT_MODULE, 'O', ' ' },
{ TAINT_UNSIGNED_MODULE, 'E', ' ' },
{ TAINT_SOFTLOCKUP, 'L', ' ' },
+ { TAINT_PERFORMANCE, 'Q', ' ' },
};
/**
@@ -501,3 +502,42 @@ static int __init oops_setup(char *s)
return 0;
}
early_param("oops", oops_setup);
+
+#ifdef CONFIG_DEBUG_KERNEL
+#define TAINT_PERF_IF(x) do { \
+ if (IS_ENABLED(CONFIG_##x)) { \
+ do_taint = 1; \
+ pr_warn("CONFIG_%s enabled\n", __stringify(x));\
+ } \
+ } while (0)
+
+static int __init performance_taint(void)
+{
+ int do_taint = 0;
+
+ /*
+ * This should list any kernel options that can substantially
+ * affect performance. This is intended to give a big, fat
+ * warning during bootup so that folks have a fighting chance
+ * of noticing these things.
+ */
+ TAINT_PERF_IF(LOCKDEP);
+ TAINT_PERF_IF(LOCK_STAT);
+ TAINT_PERF_IF(DEBUG_VM);
+ TAINT_PERF_IF(DEBUG_VM_VMACACHE);
+ TAINT_PERF_IF(DEBUG_VM_RB);
+ TAINT_PERF_IF(DEBUG_SLAB);
+ TAINT_PERF_IF(DEBUG_OBJECTS_FREE);
+ TAINT_PERF_IF(DEBUG_KMEMLEAK);
+ TAINT_PERF_IF(SCHEDSTATS);
+
+ if (!do_taint)
+ return 0;
+
+ pr_warn("Do not use this kernel for performance measurement.");
+ dump_stack();
+ add_taint(TAINT_PERFORMANCE, LOCKDEP_STILL_OK);
+ return 0;
+}
+late_initcall(performance_taint);
+#endif
_
--
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