Messages in this thread Patch in this message | | | Date | Thu, 30 May 2002 10:46:08 -0700 | From | Dave Hansen <> | Subject | [RFC] better spinlock profiling for readprofile |
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Lockmeter tends to be a pretty blunt object for most jobs. In a lot of cases, I just want to see if any locks are taking a significant amount of CPU time.
Right now, the profile looks like this: 21 .text.lock.sched 1.3125 the "sched" comes from a define on the gcc command line, like this: gcc ... -DKBUILD_BASENAME=sched -c -o sched.o sched.c
What I really want to know is not in which file, but which lock is being contended. After beating myself over the head I decided that this is impossible to do with the compiler itself. The best I could come up with was to use __LINE__ and __FUNCTION__. Because of __FUNCTION__ I had to make spin_lock() a macro again (at least for 386), but it lets me get results like this:
21 .text.lock.sched.schedule.848 1.3125
Now, I know that the contention comes from this line: reacquire_kernel_lock(current); as opposed to one of the runqueue locks or something else funky in sched.c.
Changing the inline function spin_lock() to a macro causes a loss of type safety. Some of that can be regained by the new inline function: _spin_lock_typecheck().
Is extra profiling something that could be useful in the mainline kernel, maybe as a config option? We could allow the user to select any combination of filename/function name/line. Is the System.map bloat acceptable?
WARNING! This patch may cause nausea or vomiting in people who have some concept of code decency. SPINLOCK_DEBUG is broken, and all non-x86 architectures probably don't profile correctly.
BTW, is profile=2 broken in 2.5.19? I'm only getting about 1/8 of the the load I expect: ... 2316 schedule 2.1604 7793 do_page_fault 5.6966 170298 default_idle 2660.9062 187908 total 1.4447
I have the feeling that it is only profiling 1 of my 8 cpus and calling the rest idle.
-- Dave Hansen haveblue@us.ibm.com diff -ur linux-2.5.19-clean/include/asm-i386/spinlock.h linux-2.5.19/include/asm-i386/spinlock.h --- linux-2.5.19-clean/include/asm-i386/spinlock.h Wed May 29 11:42:49 2002 +++ linux-2.5.19/include/asm-i386/spinlock.h Wed May 29 16:21:48 2002 @@ -123,21 +123,15 @@ return oldval > 0; } -static inline void _raw_spin_lock(spinlock_t *lock) -{ -#if SPINLOCK_DEBUG - __label__ here; -here: - if (lock->magic != SPINLOCK_MAGIC) { -printk("eip: %p\n", &&here); - BUG(); - } -#endif - __asm__ __volatile__( - spin_lock_string - :"=m" (lock->lock) : : "memory"); -} +static inline void _spin_lock_typecheck(spinlock_t *lock) {} +#define _raw_spin_lock(spinlock)\ +do {\ + _spin_lock_typecheck(spinlock);\ + __asm__ __volatile__(\ + spin_lock_string\ + :"=m" ((spinlock)->lock) : : "memory");\ +} while(0) /* * Read-write spinlocks, allowing multiple readers diff -ur linux-2.5.19-clean/include/linux/spinlock.h linux-2.5.19/include/linux/spinlock.h --- linux-2.5.19-clean/include/linux/spinlock.h Wed May 29 11:42:55 2002 +++ linux-2.5.19/include/linux/spinlock.h Wed May 29 17:16:05 2002 @@ -44,7 +44,7 @@ #include <linux/stringify.h> #define LOCK_SECTION_NAME \ - ".text.lock." __stringify(KBUILD_BASENAME) + ".text.lock." __stringify(KBUILD_BASENAME) "." __FUNCTION__ "." __stringify(__LINE__) #define LOCK_SECTION_START(extra) \ ".subsection 1\n\t" \ | |