--- linux-2.6.29-gs3.2-bfq/arch/x86/Kconfig.debug	2009-03-24 00:12:14.000000000 +0100
+++ linux-2.6.29-gs3.2-bfq-qtrace/arch/x86/Kconfig.debug	2009-10-05 15:44:58.766288048 +0200
@@ -5,6 +5,12 @@ config TRACE_IRQFLAGS_SUPPORT
 
 source "lib/Kconfig.debug"
 
+config QOSTRACE
+	bool "Low overhead profiling of system calls"
+	default y
+	---help---
+	  Use this only if you know what it means.
+
 config STRICT_DEVMEM
 	bool "Filter access to /dev/mem"
 	help
--- linux-2.6.29-gs3.2-bfq/arch/x86/include/asm/thread_info.h	2009-03-24 00:12:14.000000000 +0100
+++ linux-2.6.29-gs3.2-bfq-qtrace/arch/x86/include/asm/thread_info.h	2009-10-05 16:02:19.832696426 +0200
@@ -94,6 +94,8 @@ struct thread_info {
 #define TIF_DEBUGCTLMSR		25	/* uses thread_struct.debugctlmsr */
 #define TIF_DS_AREA_MSR		26      /* uses thread_struct.ds_area_msr */
 
+#define TIF_SYSCALL_QOSTRACE	29      /* for me */
+
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
@@ -115,14 +117,18 @@ struct thread_info {
 #define _TIF_DEBUGCTLMSR	(1 << TIF_DEBUGCTLMSR)
 #define _TIF_DS_AREA_MSR	(1 << TIF_DS_AREA_MSR)
 
+#define _TIF_SYSCALL_QOSTRACE	(1 << TIF_SYSCALL_QOSTRACE)
+
 /* work to do in syscall_trace_enter() */
 #define _TIF_WORK_SYSCALL_ENTRY	\
 	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU | \
-	 _TIF_SYSCALL_AUDIT | _TIF_SECCOMP | _TIF_SINGLESTEP)
+	 _TIF_SYSCALL_AUDIT | _TIF_SECCOMP | _TIF_SINGLESTEP | \
+	 _TIF_SYSCALL_QOSTRACE)
 
 /* work to do in syscall_trace_leave() */
 #define _TIF_WORK_SYSCALL_EXIT	\
-	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SINGLESTEP)
+	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SINGLESTEP | \
+	 _TIF_SYSCALL_QOSTRACE)
 
 /* work to do on interrupt/exception return */
 #define _TIF_WORK_MASK							\
@@ -131,7 +137,7 @@ struct thread_info {
 	   _TIF_SINGLESTEP|_TIF_SECCOMP|_TIF_SYSCALL_EMU))
 
 /* work to do on any return to user space */
-#define _TIF_ALLWORK_MASK (0x0000FFFF & ~_TIF_SECCOMP)
+#define _TIF_ALLWORK_MASK ((0x0000FFFF & ~_TIF_SECCOMP)|_TIF_SYSCALL_QOSTRACE)
 
 /* Only used for 64 bit */
 #define _TIF_DO_NOTIFY_MASK						\
--- linux-2.6.29-gs3.2-bfq/arch/x86/kernel/ptrace.c	2009-03-24 00:12:14.000000000 +0100
+++ linux-2.6.29-gs3.2-bfq-qtrace/arch/x86/kernel/ptrace.c	2009-10-05 20:19:13.298258905 +0200
@@ -21,6 +21,9 @@
 #include <linux/audit.h>
 #include <linux/seccomp.h>
 #include <linux/signal.h>
+#include <linux/module.h>
+#include <linux/miscdevice.h>
+#include <linux/bitmap.h>
 
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
@@ -60,6 +63,165 @@ enum x86_regset {
 				  X86_EFLAGS_DF | X86_EFLAGS_OF |	\
 				  X86_EFLAGS_RF | X86_EFLAGS_AC))
 
+#define QOSTRACE_LEAVE		0x10000
+#define QOSTRACE_ENTER		0x20000
+
+#ifdef CONFIG_QOSTRACE
+struct qostrace_event {
+	int event;
+	int pid;
+	struct timespec time;
+};
+
+#define QOSTRACE_NR_SYSCALLS	300
+#define QOSTRACE_MAX_EVENTS	32768
+
+static spinlock_t qostrace_lock;
+static DECLARE_BITMAP(qostrace_enabled, QOSTRACE_NR_SYSCALLS);
+static int qostrace_first, qostrace_last;
+static struct qostrace_event qostrace_events[QOSTRACE_MAX_EVENTS];
+
+static inline int qostrace_get(char __user *buf)
+{
+	struct qostrace_event *event;
+
+	spin_lock(&qostrace_lock);
+	if (qostrace_first == qostrace_last) {
+		spin_unlock(&qostrace_lock);
+		return 0;
+	}
+
+	event = &qostrace_events[qostrace_first];
+	qostrace_first = (qostrace_first + 1) % QOSTRACE_MAX_EVENTS;
+	spin_unlock(&qostrace_lock);
+
+	put_user(event->event, (u32 *)buf);
+	put_user(event->pid, (u32 *)buf + 1);
+	put_user(event->time.tv_sec, (u32 *)buf + 2);
+	put_user(event->time.tv_nsec, (u32 *)buf + 3);
+
+	return 16;
+}
+
+static ssize_t qostrace_read(struct file *file, char __user *buf,
+			     size_t count, loff_t *ppos)
+{
+	int i = 0, v = 1, ret = 0;
+
+	for (i = 0; i < count / 16 && v; i++) {
+		v = qostrace_get(buf);
+		ret += v;
+	}
+
+	return ret;
+}
+
+static ssize_t qostrace_write(struct file *file, const char __user *buf,
+			      size_t count, loff_t *ppos)
+{
+	int cmd, id, enabled, ret = 2 * sizeof(int);
+	struct task_struct *p;
+
+	get_user(cmd, (int *)buf);
+	get_user(id, (int *)buf + 1);
+	get_user(enabled, (int *)buf + 2);
+
+	spin_lock(&qostrace_lock);
+	switch (cmd) {
+	case 0:
+		if (id < 0 || id > QOSTRACE_NR_SYSCALLS)
+			ret = -EINVAL;
+		else if (enabled)
+			__set_bit(id, qostrace_enabled);
+		else
+			__clear_bit(id, qostrace_enabled);
+		break;
+	case 1:
+		p = find_task_by_vpid(id);
+		if (!p)
+			ret = -EINVAL;
+		else if (enabled)
+			set_tsk_thread_flag(p, TIF_SYSCALL_QOSTRACE);
+		else
+			clear_tsk_thread_flag(p, TIF_SYSCALL_QOSTRACE);
+		break;
+	case 2:
+		qostrace_first = qostrace_last = 0;
+		break;
+	default:
+		ret = -EINVAL;
+	}
+	spin_unlock(&qostrace_lock);
+
+	return ret;
+}
+
+static int qostrace_open(struct inode *inode, struct file *file)
+{
+	return 0;
+}
+
+static int qostrace_release(struct inode *inode, struct file *file)
+{
+	return 0;
+}
+
+static const struct file_operations qostrace_dev_fops = {
+	.owner		= THIS_MODULE,
+	.llseek		= no_llseek,
+	.read		= qostrace_read,
+	.write		= qostrace_write,
+	.open		= qostrace_open,
+	.release	= qostrace_release,
+};
+
+static struct miscdevice qostrace_miscdev = {
+	.minor		= MISC_DYNAMIC_MINOR,
+	.name		= "qostrace",
+	.fops		= &qostrace_dev_fops,
+};
+
+extern void getnstimeofday(struct timespec *ts);
+
+static inline void qostrace_clock(struct timespec *time)
+{
+	getnstimeofday(time);
+}
+
+static inline void qostrace_syscall(struct pt_regs *regs, int evmask)
+{
+	struct qostrace_event *event;
+	int id = regs->orig_ax;
+
+	if (id < 0 || id > QOSTRACE_NR_SYSCALLS ||
+	    !test_bit(id, qostrace_enabled))
+		return;
+
+	spin_lock(&qostrace_lock);
+	if ((qostrace_last + 1) % QOSTRACE_MAX_EVENTS != qostrace_first) {
+		event = &qostrace_events[qostrace_last];
+		qostrace_last = (qostrace_last + 1) % QOSTRACE_MAX_EVENTS;
+
+		event->event = id | evmask;
+		/* XXX could be done better, see how it works */
+		event->pid = current->tgid;
+		qostrace_clock(&event->time);
+	}
+	spin_unlock(&qostrace_lock);
+}
+
+static int __init qostrace_init(void)
+{
+	spin_lock_init(&qostrace_lock);
+	return misc_register(&qostrace_miscdev);
+}
+late_initcall(qostrace_init);
+#else
+static inline void qostrace_syscall(struct pt_regs *regs, int evmask)
+{
+}
+#endif
+
 /*
  * Determines whether a value may be installed in a segment register.
  */
@@ -1421,6 +1583,9 @@ asmregparm long syscall_trace_enter(stru
 	    tracehook_report_syscall_entry(regs))
 		ret = -1L;
 
+	if (unlikely(test_thread_flag(TIF_SYSCALL_QOSTRACE)))
+		qostrace_syscall(regs, QOSTRACE_ENTER);
+
 	if (unlikely(current->audit_context)) {
 		if (IS_IA32)
 			audit_syscall_entry(AUDIT_ARCH_I386,
@@ -1447,6 +1612,9 @@ asmregparm void syscall_trace_leave(stru
 	if (test_thread_flag(TIF_SYSCALL_TRACE))
 		tracehook_report_syscall_exit(regs, 0);
 
+	if (unlikely(test_thread_flag(TIF_SYSCALL_QOSTRACE)))
+		qostrace_syscall(regs, QOSTRACE_LEAVE);
+
 	/*
 	 * If TIF_SYSCALL_EMU is set, we only get here because of
 	 * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).