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SubjectRe: [PATCH] 2.4.18-pre9, trylock for read/write semaphores
"Kendrick M. Smith" wrote:
> I have the patch from your original post and will give it a try with
> 2.5. In that post, you also mentioned having some sort of testsuite
> which would place the semaphore under heavy contention, while also
> testing basic semantics of the semaphore. If you send this along, I
> will give it a try as well...

The testsuite patch is attached. Apply it after the rwsem trylock patch.
What it does is start ten kernel threads that randomly call down_read,
down_write, down_read_trylock, and down_write_trylock. Reboot with the
test kernel and let it run for awhile. It should give your hard drive a
good workout as the debug output is written to the log. After a few
thousand locking operations, reboot with an ordinary kernel and study
the log.

If you have questions about the debug output, let me know.

--
Brian Watson | "Now I don't know, but I been told it's
Linux Kernel Developer | hard to run with the weight of gold,
Open SSI Clustering Project | Other hand I heard it said, it's
Compaq Computer Corp | just as hard with the weight of lead."
Los Angeles, CA | -Robert Hunter, 1970

mailto:Brian.J.Watson@compaq.com
http://opensource.compaq.com/diff -Naur rwsem/include/asm-i386/rwsem.h rwsem-test/include/asm-i386/rwsem.h
--- rwsem/include/asm-i386/rwsem.h Mon Feb 18 18:46:18 2002
+++ rwsem-test/include/asm-i386/rwsem.h Mon Feb 18 18:18:02 2002
@@ -120,9 +120,30 @@
: "memory", "cc");
}

+void rst_debug_print(signed long ctr);
+
/*
* trylock for reading -- returns 1 if successful, 0 if contention
*/
+#if 0
+static inline int __down_read_trylock(struct rw_semaphore *sem)
+{
+ signed long old, new, result;
+
+repeat:
+ old = (volatile signed long)sem->count;
+ if (old < RWSEM_UNLOCKED_VALUE)
+ return 0;
+ new = old + RWSEM_ACTIVE_READ_BIAS;
+ result = cmpxchg(&sem->count, old, new);
+ rst_debug_print(result);
+ if (result == old)
+ return 1;
+ else
+ goto repeat;
+}
+#endif
+
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
__s32 result, tmp;
@@ -140,6 +161,7 @@
: "+m"(sem->count), "=&a"(result), "+&r"(tmp)
: "i"(RWSEM_ACTIVE_READ_BIAS)
: "memory", "cc");
+ rst_debug_print(result);
return result>=0 ? 1 : 0;
}

@@ -181,6 +203,7 @@
signed long ret = cmpxchg(&sem->count,
RWSEM_UNLOCKED_VALUE,
RWSEM_ACTIVE_WRITE_BIAS);
+ rst_debug_print(ret);
if (ret == RWSEM_UNLOCKED_VALUE)
return 1;
return 0;
diff -Naur rwsem/include/linux/rwsem.h rwsem-test/include/linux/rwsem.h
--- rwsem/include/linux/rwsem.h Mon Feb 18 18:44:36 2002
+++ rwsem-test/include/linux/rwsem.h Mon Feb 18 18:18:07 2002
@@ -9,7 +9,7 @@

#include <linux/linkage.h>

-#define RWSEM_DEBUG 0
+#define RWSEM_DEBUG 1

#ifdef __KERNEL__

diff -Naur rwsem/include/rwsem_test.h rwsem-test/include/rwsem_test.h
--- rwsem/include/rwsem_test.h Wed Dec 31 16:00:00 1969
+++ rwsem-test/include/rwsem_test.h Mon Feb 18 15:36:44 2002
@@ -0,0 +1,100 @@
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <linux/random.h>
+#include <linux/rwsem.h>
+#include <linux/spinlock.h>
+
+DECLARE_RWSEM(rst_lock);
+
+spinlock_t rst_ctrlock = SPIN_LOCK_UNLOCKED;
+unsigned int rst_ctr = 1000;
+unsigned int getctr(void)
+{
+ unsigned long ret;
+ spin_lock(&rst_ctrlock);
+ ret = ++rst_ctr;
+ spin_unlock(&rst_ctrlock);
+ return ret;
+}
+
+void rst_debug_print(signed long ctr)
+{
+ printk("[rst %d:%d] rwsem counter: %x\n", current->pid, getctr(), (unsigned int)ctr);
+}
+
+int
+rst_daemon(void *ignore)
+{
+ while (1) {
+ unsigned char sleep, style, ctr = 0;
+
+ get_random_bytes(&sleep, 1);
+ __set_current_state(TASK_UNINTERRUPTIBLE);
+ schedule_timeout((signed long)sleep);
+
+ for (; ctr < 20; ++ctr) {
+ get_random_bytes(&style, 1);
+
+ if (style > 191) {
+ down_write(&rst_lock);
+ printk("[rst %d:%d] down_write\n", current->pid, getctr());
+ } else if (style > 127) {
+ if (!down_write_trylock(&rst_lock)) {
+ printk("[rst %d:%d] down_write_trylock "
+ "failed\n",
+ current->pid, getctr());
+ break;
+ }
+ printk("[rst %d:%d] down_write_trylock "
+ "succeeded\n", current->pid, getctr());
+ } else if (style > 63) {
+ down_read(&rst_lock);
+ printk("[rst %d:%d] down_read\n", current->pid, getctr());
+ } else {
+ if (!down_read_trylock(&rst_lock)) {
+ printk("[rst %d:%d] down_read_trylock "
+ "failed\n",
+ current->pid, getctr());
+ break;
+ }
+ printk("[rst %d:%d] down_read_trylock "
+ "succeeded\n", current->pid, getctr());
+ }
+
+ if (style > 127)
+ printk("[rst %d:%d] writing... [1]\n",
+ current->pid, getctr());
+ else
+ printk("[rst %d:%d] reading... [1]\n",
+ current->pid, getctr());
+
+ __set_current_state(TASK_UNINTERRUPTIBLE);
+ schedule_timeout(5);
+
+ if (style > 127)
+ printk("[rst %d:%d] writing... [2]\n",
+ current->pid, getctr());
+ else
+ printk("[rst %d:%d] reading... [2]\n",
+ current->pid, getctr());
+
+ if (style > 127) {
+ printk("[rst %d:%d] up_write\n", current->pid, getctr());
+ up_write(&rst_lock);
+ } else {
+ printk("[rst %d:%d] up_read\n", current->pid, getctr());
+ up_read(&rst_lock);
+ }
+ }
+ }
+ return 0;
+}
+
+void
+rst_init(void)
+{
+ int ctr = 0;
+ rst_lock.debug = 1;
+ for (; ctr < 10; ++ctr)
+ kernel_thread(rst_daemon, NULL, 0);
+}
diff -Naur rwsem/init/main.c rwsem-test/init/main.c
--- rwsem/init/main.c Mon Feb 18 18:45:30 2002
+++ rwsem-test/init/main.c Mon Feb 18 14:11:23 2002
@@ -31,6 +31,8 @@
#include <asm/io.h>
#include <asm/bugs.h>

+#include <rwsem_test.h>
+
#if defined(CONFIG_ARCH_S390)
#include <asm/s390mach.h>
#include <asm/ccwcache.h>
@@ -829,6 +831,8 @@
* The Bourne shell can be used instead of init if we are
* trying to recover a really broken machine.
*/
+
+ rst_init();

if (execute_command)
execve(execute_command,argv_init,envp_init);
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