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debug_maxlat as module_param

PATCH In review Jan Kiszka 4 participants 5 messages Dec 17, 2005 – Dec 18, 2005 Kbuild

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Jan Kiszka

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#0 lore raw

PATCH 1/1 debug_maxlat as module_param

Hi,

this tiny patch exports the NMI watchdog's threshold as module parameter "debug_maxlat" of xeno_hal. This means that one can either override the value via a kernel parameter or in sysfs/modules/xeno_hal/parameters (before activating the hal).

Unfortunately, this tiny patch caused some headache to me as it first made the kernel crash early during boot in sysfs_create_group(). I do not understand why I need the second patch, I only guessed from the kernel build output that some unlucky linking order screwed up module_params in xenomai's non-generic arch files. If this is the only solution, we have to verify if 2.4 still works (untested) and we have to patch the Makefiles of the other archs.

Jan

PS: The NMI watchdog is nice, but we are really lacking a qualified backtrace with all invoked functions in a critical path. I'm optimistic that we will see Fu's first latency trace patch version already next week. :)

arch/i386/hal.c +5 -4
Index: ksrc/arch/i386/hal.c
===================================================================
@@ -212,7 +212,8 @@
 unsigned long rthal_maxlat_tsc;
 EXPORT_SYMBOL(rthal_maxlat_tsc);
 
-static unsigned rthal_maxlat_us = CONFIG_XENO_HW_NMI_DEBUG_LATENCY_MAX;
+unsigned rthal_maxlat_us_arg = CONFIG_XENO_HW_NMI_DEBUG_LATENCY_MAX;
+module_param_named(debug_maxlat, rthal_maxlat_us_arg, uint, 0644);
 
 static void rthal_latency_above_max(struct pt_regs *regs)
 {

@@ -220,7 +221,7 @@
     snprintf(buf,
              sizeof(buf),
              "NMI watchdog detected timer latency above %u us\n",
-             rthal_maxlat_us);
+             rthal_maxlat_us_arg);
     die_nmi(regs, buf);
 }
 #endif

@@ -297,7 +298,7 @@
 
 #ifdef CONFIG_XENO_HW_NMI_DEBUG_LATENCY
     if (!p->mode) {
-        rthal_maxlat_tsc = rthal_llimd(rthal_maxlat_us * 1000ULL,
+        rthal_maxlat_tsc = rthal_llimd(rthal_maxlat_us_arg * 1000ULL,
                                        RTHAL_CPU_FREQ,
                                        1000000000);
 

@@ -307,7 +308,7 @@
             printk("Xenomai: NMI watchdog not available.\n");
         else
             printk("Xenomai: NMI watchdog started (threshold=%u us).\n",
-		   rthal_maxlat_us);
+		   rthal_maxlat_us_arg);
     }
 #endif /* CONFIG_XENO_HW_NMI_DEBUG_LATENCY */
prepare-kernel.sh +1 -0
Index: scripts/prepare-kernel.sh
===================================================================
@@ -301,6 +301,7 @@
 # compilation files.
 
 do_links $xenomai_root/ksrc/arch/$xenomai_arch $linux_tree/arch/$linux_arch/xenomai
+do_links $xenomai_root/ksrc/arch/generic $linux_tree/arch/$linux_arch/xenomai/generic
 do_links $xenomai_root/ksrc $linux_tree/kernel/xenomai
 do_links $xenomai_root/ksrc/drivers $linux_tree/drivers/xenomai
 do_links $xenomai_root/include/asm-$xenomai_arch $linux_tree/include/asm-$linux_arch/xenomai
Makefile +1 -3
Index: ksrc/Makefile
===================================================================
@@ -2,14 +2,12 @@
 
 # Makefile frag for Linux v2.6
 
-obj-$(CONFIG_XENOMAI) += arch/ nucleus/ skins/
+obj-$(CONFIG_XENOMAI) += nucleus/ skins/
 
 else
 
 # Makefile frag for Linux v2.4
 
-subdir-$(CONFIG_XENOMAI) += arch
-
 subdir-$(CONFIG_XENO_OPT_NUCLEUS) += nucleus
 
 mod-subdirs := skins
arch/Makefile +0 -15
Index: ksrc/arch/Makefile
===================================================================
@@ -1,15 +0,0 @@
-ifeq ($(PATCHLEVEL),6)
-
-# Makefile frag for Linux v2.6
-
-obj-$(CONFIG_XENOMAI) += generic/
-
-else
-
-# Makefile frag for Linux v2.4
-
-subdir-y += generic
-
-include $(TOPDIR)/Rules.make
-
-endif
arch/i386/Makefile +3 -1
Index: ksrc/arch/i386/Makefile
===================================================================
@@ -2,7 +2,7 @@
 
 # Makefile frag for Linux v2.6
 
-obj-$(CONFIG_XENOMAI) += xeno_hal.o
+obj-$(CONFIG_XENOMAI) += xeno_hal.o generic/
 
 xeno_hal-y := hal.o usercopy.o
 

@@ -14,6 +14,8 @@
 
 # Makefile frag for Linux v2.4
 
+subdir-y += generic
+
 USE_STANDARD_AS_RULE := true
 
 O_TARGET := built-in.o
#1 lore raw
Quoted 6 lines · Jan Kiszka

Hi,

this tiny patch exports the NMI watchdog's threshold as module parameter "debug_maxlat" of xeno_hal. This means that one can either override the value via a kernel parameter or in sysfs/modules/xeno_hal/parameters (before activating the hal).

rthal_maxlat_tsc should be updated when rthal_maxlat_us_arg changes.

Signature · 1 line
					    Gilles Chanteperdrix.
#2 lore raw
Quoted 10 lines · Gilles Chanteperdrix
Quoted 6 lines · Jan Kiszka

Hi,

this tiny patch exports the NMI watchdog's threshold as module parameter "debug_maxlat" of xeno_hal. This means that one can either override the value via a kernel parameter or in sysfs/modules/xeno_hal/parameters (before activating the hal).

rthal_maxlat_tsc should be updated when rthal_maxlat_us_arg changes.

I didn't digged that deep, is this possible during runtime? My current workflow looks like this: unload xeno_nucleus (and higher modules), change maxlat, reload the modules.

Mmh, I guess one has to register some update handler with sysfs in that case. Any hint where to look for a pattern?

Jan

#3 lore raw
Quoted 14 lines · Jan Kiszka
Quoted 10 lines · Gilles Chanteperdrix
Quoted 6 lines · Jan Kiszka

Hi,

this tiny patch exports the NMI watchdog's threshold as module parameter "debug_maxlat" of xeno_hal. This means that one can either override the value via a kernel parameter or in sysfs/modules/xeno_hal/parameters (before activating the hal).

rthal_maxlat_tsc should be updated when rthal_maxlat_us_arg changes.

Quoted 7 lines

I didn't digged that deep, is this possible during runtime? My current workflow looks like this: unload xeno_nucleus (and higher modules), change maxlat, reload the modules.

Mmh, I guess one has to register some update handler with sysfs in that case. Any hint where to look for a pattern?

Please don't depend on sysfs for generic features since they would not be available on 2.4.

Quoted 9 lines

Jan

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Signature · 1 line
Philippe.
#4 lore raw
In reply to Jan Kiszka
Quoted 12 lines · Jan Kiszka
Quoted 10 lines · Gilles Chanteperdrix
Quoted 6 lines · Jan Kiszka

Hi,

this tiny patch exports the NMI watchdog's threshold as module parameter "debug_maxlat" of xeno_hal. This means that one can either override the value via a kernel parameter or in sysfs/modules/xeno_hal/parameters (before activating the hal).

rthal_maxlat_tsc should be updated when rthal_maxlat_us_arg changes.

Quoted 6 lines

I didn't digged that deep, is this possible during runtime? My current workflow looks like this: unload xeno_nucleus (and higher modules), change maxlat, reload the modules.

Mmh, I guess one has to register some update handler with sysfs in that case. Any hint where to look for a pattern?

In nucleus/module.c, the latency parameter may be read and written at run-time through procfs, have a look at the functions latency_read_proc and latency_write_proc.

Signature · 1 line
					    Gilles Chanteperdrix.