Index: linux-2.6.21-rc5/lib/Kconfig.debug
===================================================================
--- linux-2.6.21-rc5.orig/lib/Kconfig.debug
+++ linux-2.6.21-rc5/lib/Kconfig.debug
@@ -458,6 +458,6 @@ config THREAD_PERF_STAT
 
 config THREAD_PERF_STAT_SYSC
        bool "Enable syscall counter"
-       depends on THREAD_PERF_STAT && X86_32
+       depends on THREAD_PERF_STAT && X86
        help
          This option adds a syscall counter to /proc/PID/status.
Index: linux-2.6.21-rc5/include/asm-x86_64/thread_info.h
===================================================================
--- linux-2.6.21-rc5.orig/include/asm-x86_64/thread_info.h
+++ linux-2.6.21-rc5/include/asm-x86_64/thread_info.h
@@ -30,7 +30,9 @@ struct thread_info {
 	__u32			status;		/* thread synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int 			preempt_count;	/* 0 => preemptable, <0 => BUG */
-
+#ifdef CONFIG_THREAD_PERF_STAT_SYSC
+	unsigned long		sysc_cnt;	/* Syscall counter */
+#endif /* CONFIG_THREAD_PERF_STAT_SYSC */
 	mm_segment_t		addr_limit;	
 	struct restart_block    restart_block;
 };
Index: linux-2.6.21-rc5/arch/x86_64/kernel/entry.S
===================================================================
--- linux-2.6.21-rc5.orig/arch/x86_64/kernel/entry.S
+++ linux-2.6.21-rc5/arch/x86_64/kernel/entry.S
@@ -236,6 +236,11 @@ ENTRY(system_call)
 	movq %r10,%rcx
 	call *sys_call_table(,%rax,8)  # XXX:	 rip relative
 	movq %rax,RAX-ARGOFFSET(%rsp)
+#ifdef CONFIG_THREAD_PERF_STAT_SYSC
+	GET_THREAD_INFO(%rcx)
+	addq $1, threadinfo_sysc_cnt(%rcx)   # Increment syscalls counter
+#endif /* CONFIG_THREAD_PERF_STAT_SYSC */
+
 /*
  * Syscall return path ending with SYSRET (fast path)
  * Has incomplete stack frame and undefined top of stack. 
@@ -319,6 +324,10 @@ tracesys:			 
 	call *sys_call_table(,%rax,8)
 1:	movq %rax,RAX-ARGOFFSET(%rsp)
 	/* Use IRET because user could have changed frame */
+#ifdef CONFIG_THREAD_PERF_STAT_SYSC
+	GET_THREAD_INFO(%rcx)
+	addq $1, threadinfo_sysc_cnt(%rcx)   # Increment syscalls counter
+#endif /* CONFIG_THREAD_PERF_STAT_SYSC */
 		
 /* 
  * Syscall return path ending with IRET.
Index: linux-2.6.21-rc5/arch/x86_64/kernel/asm-offsets.c
===================================================================
--- linux-2.6.21-rc5.orig/arch/x86_64/kernel/asm-offsets.c
+++ linux-2.6.21-rc5/arch/x86_64/kernel/asm-offsets.c
@@ -35,6 +35,9 @@ int main(void)
 	ENTRY(addr_limit);
 	ENTRY(preempt_count);
 	ENTRY(status);
+#ifdef CONFIG_THREAD_PERF_STAT_SYSC 
+	ENTRY(sysc_cnt);
+#endif /* CONFIG_THREAD_PERF_STAT_SYSC */
 	BLANK();
 #undef ENTRY
 #define ENTRY(entry) DEFINE(pda_ ## entry, offsetof(struct x8664_pda, entry))