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Message-ID: <20080616075832.GE6950@cs.unibo.it>
Date: Mon, 16 Jun 2008 09:58:32 +0200
From: renzo@...unibo.it (Renzo Davoli)
To: LKML <linux-kernel@...r.kernel.org>, Jeff Dike <jdike@...toit.com>,
Roland McGrath <roland@...hat.com>
Subject: [PATCH 2/2] ptrace_multi: speedup for virtual machines (and debuggers) running on ptrace
Warning:
This is a proof-of-concept. It shows the effectiveness of PTRACE_MULTI
(PATCH 1/2). It is incomplete, not to be included at this stage.
This patch adds some PTRACE_MULTI optimizations to User-Mode Linux client
code. With these optimization UML decreases the overall number of
syscalls (around 15% in my preliminary tests) and shows some speedup
(5%).
I expect better figures when all the UML client code will take advantage
of PTRACE_MULTI and on other architectures (e.g. on powerpc, still
unsupported, where tens of ptrace in a row are needed to get/set
registers).
This patch is against 2.6.26-rc6 (or git2) + ptrace_multi + ptrace_vm
renzo
Signed-off-by: Renzo Davoli
---
diff -Naur linux-2.6.26-rc6-ptrace_multi-ptrace_vm/arch/um/include/ptrace_user.h linux-2.6.26-rc6-ptrace_multi-ptrace_vm-umlmulti/arch/um/include/ptrace_user.h
--- linux-2.6.26-rc6-ptrace_multi-ptrace_vm/arch/um/include/ptrace_user.h 2008-06-14 20:07:04.000000000 +0200
+++ linux-2.6.26-rc6-ptrace_multi-ptrace_vm-umlmulti/arch/um/include/ptrace_user.h 2008-06-15 18:35:28.000000000 +0200
@@ -20,6 +20,18 @@
#define PTRACE_SYSEMU_SINGLESTEP 32
#endif
+#define PTRACE_MULTI 0x4300
+#define PTRACE_PEEKCHARDATA 0x4301
+#define PTRACE_POKECHARDATA 0x4302
+#define PTRACE_PEEKSTRINGDATA 0x4303
+
+struct ptrace_multi {
+ long request;
+ long addr;
+ void *localaddr;
+ long length;
+};
+
/* On architectures, that started to support PTRACE_O_TRACESYSGOOD
* in linux 2.4, there are two different definitions of
* PTRACE_SETOPTIONS: linux 2.4 uses 21 while linux 2.6 uses 0x4200.
@@ -54,6 +66,9 @@
void set_using_sysptvm(int value);
int get_using_sysptvm(void);
extern int sysptvm_supported;
+void set_using_sysptmulti(int value);
+int get_using_sysptmulti(void);
+extern int sysptmulti_supported;
#define SELECT_PTRACE_OPERATION(sysemu_mode, singlestep_mode) \
(((int[3][3] ) { \
diff -Naur linux-2.6.26-rc6-ptrace_multi-ptrace_vm/arch/um/kernel/process.c linux-2.6.26-rc6-ptrace_multi-ptrace_vm-umlmulti/arch/um/kernel/process.c
--- linux-2.6.26-rc6-ptrace_multi-ptrace_vm/arch/um/kernel/process.c 2008-06-14 20:07:04.000000000 +0200
+++ linux-2.6.26-rc6-ptrace_multi-ptrace_vm-umlmulti/arch/um/kernel/process.c 2008-06-15 18:35:28.000000000 +0200
@@ -323,8 +323,10 @@
static atomic_t using_sysemu = ATOMIC_INIT(0);
static atomic_t using_sysptvm = ATOMIC_INIT(0);
+static atomic_t using_sysptmulti = ATOMIC_INIT(0);
int sysemu_supported;
int sysptvm_supported;
+int sysptmulti_supported;
void set_using_sysemu(int value)
{
@@ -348,6 +350,16 @@
return atomic_read(&using_sysptvm);
}
+void set_using_sysptmulti(int value)
+{
+ atomic_set(&using_sysptmulti, value);
+}
+
+int get_using_sysptmulti(void)
+{
+ return atomic_read(&using_sysptmulti);
+}
+
static int proc_read_sysemu(char *buf, char **start, off_t offset, int size,int *eof, void *data)
{
if (snprintf(buf, size, "%d\n", get_using_sysemu()) < size)
@@ -395,6 +407,28 @@
return count;
}
+static int proc_read_sysptmulti(char *buf, char **start, off_t offset, int size,int *eof, void *data)
+{
+ if (snprintf(buf, size, "%d\n", get_using_sysptmulti()) < size)
+ /* No overflow */
+ *eof = 1;
+
+ return strlen(buf);
+}
+
+static int proc_write_sysptmulti(struct file *file,const char __user *buf, unsigned long count,void *data)
+{
+ char tmp[2];
+
+ if (copy_from_user(tmp, buf, 1))
+ return -EFAULT;
+
+ if (tmp[0] >= '0' && tmp[0] <= '2')
+ set_using_sysptmulti(tmp[0] - '0');
+ /* We use the first char, but pretend to write everything */
+ return count;
+}
+
int __init make_proc_sysemu_or_sysptvm(void)
{
struct proc_dir_entry *ent;
@@ -422,6 +456,18 @@
ent->read_proc = proc_read_sysemu;
ent->write_proc = proc_write_sysemu;
}
+ if (sysptmulti_supported) {
+ ent = create_proc_entry("sysptmulti", 0600, NULL);
+
+ if (ent == NULL)
+ {
+ printk(KERN_WARNING "Failed to register /proc/sysptmulti\n");
+ return 0;
+ }
+
+ ent->read_proc = proc_read_sysptmulti;
+ ent->write_proc = proc_write_sysptmulti;
+ }
return 0;
}
diff -Naur linux-2.6.26-rc6-ptrace_multi-ptrace_vm/arch/um/os-Linux/skas/mem.c linux-2.6.26-rc6-ptrace_multi-ptrace_vm-umlmulti/arch/um/os-Linux/skas/mem.c
--- linux-2.6.26-rc6-ptrace_multi-ptrace_vm/arch/um/os-Linux/skas/mem.c 2008-06-14 20:06:12.000000000 +0200
+++ linux-2.6.26-rc6-ptrace_multi-ptrace_vm-umlmulti/arch/um/os-Linux/skas/mem.c 2008-06-16 01:47:34.000000000 +0200
@@ -69,19 +69,32 @@
multi_count++;
- n = ptrace_setregs(pid, syscall_regs);
- if (n < 0) {
- printk(UM_KERN_ERR "Registers - \n");
- for (i = 0; i < MAX_REG_NR; i++)
- printk(UM_KERN_ERR "\t%d\t0x%lx\n", i, syscall_regs[i]);
- panic("do_syscall_stub : PTRACE_SETREGS failed, errno = %d\n",
- -n);
- }
+ if (get_using_sysptmulti()) {
+ struct ptrace_multi req[] = {
+ {PTRACE_SETREGS, 0, syscall_regs, 0},
+ {PTRACE_CONT, 0, 0, 0}};
+ err=ptrace(PTRACE_MULTI,pid,req,2);
+ if (err<0) {
+ err = -errno;
+ printk(UM_KERN_ERR "do_syscall_stub: failed ptrace_multi "
+ "failed, pid = %d, errno = %d\n", pid, -err);
+ return err;
+ }
+ } else {
+ n = ptrace_setregs(pid, syscall_regs);
+ if (n < 0) {
+ printk(UM_KERN_ERR "Registers - \n");
+ for (i = 0; i < MAX_REG_NR; i++)
+ printk(UM_KERN_ERR "\t%d\t0x%lx\n", i, syscall_regs[i]);
+ panic("do_syscall_stub : PTRACE_SETREGS failed, errno = %d\n",
+ -n);
+ }
- err = ptrace(PTRACE_CONT, pid, 0, 0);
- if (err)
- panic("Failed to continue stub, pid = %d, errno = %d\n", pid,
- errno);
+ err = ptrace(PTRACE_CONT, pid, 0, 0);
+ if (err)
+ panic("Failed to continue stub, pid = %d, errno = %d\n", pid,
+ errno);
+ }
wait_stub_done(pid);
diff -Naur linux-2.6.26-rc6-ptrace_multi-ptrace_vm/arch/um/os-Linux/skas/process.c linux-2.6.26-rc6-ptrace_multi-ptrace_vm-umlmulti/arch/um/os-Linux/skas/process.c
--- linux-2.6.26-rc6-ptrace_multi-ptrace_vm/arch/um/os-Linux/skas/process.c 2008-06-14 20:07:04.000000000 +0200
+++ linux-2.6.26-rc6-ptrace_multi-ptrace_vm-umlmulti/arch/um/os-Linux/skas/process.c 2008-06-16 01:35:35.000000000 +0200
@@ -355,6 +355,7 @@
/* To prevent races if using_sysemu changes under us.*/
int local_using_sysemu;
int local_using_sysptvm;
+ int local_using_sysptmulti;
if (getitimer(ITIMER_VIRTUAL, &timer))
printk(UM_KERN_ERR "Failed to get itimer, errno = %d\n", errno);
@@ -363,41 +364,53 @@
nsecs += os_nsecs();
while (1) {
- /*
- * This can legitimately fail if the process loads a
- * bogus value into a segment register. It will
- * segfault and PTRACE_GETREGS will read that value
- * out of the process. However, PTRACE_SETREGS will
- * fail. In this case, there is nothing to do but
- * just kill the process.
- */
- if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp))
- fatal_sigsegv();
-
/* Now we set local_using_sysemu to be used for one loop */
local_using_sysemu = get_using_sysemu();
local_using_sysptvm = get_using_sysptvm();
+ local_using_sysptmulti = get_using_sysptmulti();
op = SELECT_PTRACE_OPERATION(local_using_sysemu,
- singlestepping(NULL));
+ singlestepping(NULL));
- if (ptrace(op, pid, local_using_sysptvm, 0)) {
- printk(UM_KERN_ERR "userspace - ptrace continue "
- "failed, op = %d, errno = %d\n", op, errno);
- fatal_sigsegv();
+ if (local_using_sysptmulti) {
+ struct ptrace_multi req[] = {
+ {PTRACE_SETREGS, 0, regs->gp, 0},
+ {op, local_using_sysptvm, 0, 0}};
+ if (ptrace(PTRACE_MULTI,pid,req,2)) {
+ printk(UM_KERN_ERR "userspace - ptrace multi continue "
+ "failed, op = %d, errno = %d\n", op, errno);
+ fatal_sigsegv();
+ }
+ } else {
+ /*
+ * This can legitimately fail if the process loads a
+ * bogus value into a segment register. It will
+ * segfault and PTRACE_GETREGS will read that value
+ * out of the process. However, PTRACE_SETREGS will
+ * fail. In this case, there is nothing to do but
+ * just kill the process.
+ */
+ if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp))
+ fatal_sigsegv();
+
+ if (ptrace(op, pid, local_using_sysptvm, 0)) {
+ printk(UM_KERN_ERR "userspace - ptrace continue "
+ "failed, op = %d, errno = %d\n", op, errno);
+ fatal_sigsegv();
+ }
}
CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
if (err < 0) {
printk(UM_KERN_ERR "userspace - wait failed, "
- "errno = %d\n", errno);
+ "errno = %d\n", errno);
fatal_sigsegv();
}
regs->is_user = 1;
if (ptrace(PTRACE_GETREGS, pid, 0, regs->gp)) {
printk(UM_KERN_ERR "userspace - PTRACE_GETREGS failed, "
- "errno = %d\n", errno);
+ "errno = %d\n", errno);
fatal_sigsegv();
}
@@ -497,27 +510,40 @@
{ .it_value = tv,
.it_interval = tv }) });
- err = ptrace_setregs(pid, thread_regs);
- if (err < 0) {
- err = -errno;
- printk(UM_KERN_ERR "copy_context_skas0 : PTRACE_SETREGS "
- "failed, pid = %d, errno = %d\n", pid, -err);
- return err;
- }
-
/* set a well known return code for detection of child write failure */
child_data->err = 12345678;
- /*
- * Wait, until parent has finished its work: read child's pid from
- * parent's stack, and check, if bad result.
- */
- err = ptrace(PTRACE_CONT, pid, 0, 0);
- if (err) {
- err = -errno;
- printk(UM_KERN_ERR "Failed to continue new process, pid = %d, "
- "errno = %d\n", pid, errno);
- return err;
+ if (get_using_sysptmulti()) {
+ struct ptrace_multi req[] = {
+ {PTRACE_SETREGS, 0, thread_regs, 0},
+ {PTRACE_CONT, 0, 0, 0}};
+ err=ptrace(PTRACE_MULTI,pid,req,2);
+ if (err<0) {
+ err = -errno;
+ printk(UM_KERN_ERR "copy_context_skas0: failed ptrace_multi "
+ "failed, pid = %d, errno = %d\n", pid, -err);
+ return err;
+ }
+ } else {
+ err = ptrace_setregs(pid, thread_regs);
+ if (err < 0) {
+ err = -errno;
+ printk(UM_KERN_ERR "copy_context_skas0 : PTRACE_SETREGS "
+ "failed, pid = %d, errno = %d\n", pid, -err);
+ return err;
+ }
+
+ /*
+ * Wait, until parent has finished its work: read child's pid from
+ * parent's stack, and check, if bad result.
+ */
+ err = ptrace(PTRACE_CONT, pid, 0, 0);
+ if (err) {
+ err = -errno;
+ printk(UM_KERN_ERR "Failed to continue new process, pid = %d, "
+ "errno = %d\n", pid, errno);
+ return err;
+ }
}
wait_stub_done(pid);
diff -Naur linux-2.6.26-rc6-ptrace_multi-ptrace_vm/arch/um/os-Linux/start_up.c linux-2.6.26-rc6-ptrace_multi-ptrace_vm-umlmulti/arch/um/os-Linux/start_up.c
--- linux-2.6.26-rc6-ptrace_multi-ptrace_vm/arch/um/os-Linux/start_up.c 2008-06-14 20:07:04.000000000 +0200
+++ linux-2.6.26-rc6-ptrace_multi-ptrace_vm-umlmulti/arch/um/os-Linux/start_up.c 2008-06-15 18:35:28.000000000 +0200
@@ -225,6 +225,21 @@
" Use sysemu instead of sysptvm even when the kernel supports it.\n\n"
);
+static int force_sysptmulti_disabled = 0;
+
+static int __init nosysptmulti_cmd_param(char *str, int* add)
+{
+ force_sysptmulti_disabled = 1;
+ return 0;
+}
+
+__uml_setup("nosysptmulti", nosysptmulti_cmd_param,
+ "nosysptmulti\n"
+ " Turns off syscall multi for ptrace (ptrace_vm) on.\n"
+ " Ptrace_vm is a feature introduced by Renzo Davoli: several\n"
+ " ptrace() requests can be evaluated using one system call.\n"
+ "\n");
+
static void __init check_sysemu(void)
{
unsigned long regs[MAX_REG_NR];
@@ -344,6 +359,7 @@
return 0;
}
+#define PTRACE_SUPPORTS_PTMULTI 0x80000000
/* kernel feature test:
* it returns:
* -1 error
@@ -351,7 +367,7 @@
* PTRACE_SYSCALL_SKIPEXIT: just skip_exit is provided
* PTRACE_SYSCALL_SKIPCALL: the entire syntax is implemented
* by the running kernel */
-static int __init test_ptrace_sysptvm(void) {
+static int __init test_ptrace_sysptvm_and_ptmulti(void) {
int pid, status, rv, feature;
static char stack[1024];
feature=0;
@@ -383,6 +399,8 @@
if(waitpid(pid, &status, WUNTRACED) < 0)
return 0;
out:
+ if (ptrace(PTRACE_MULTI, pid, stack, 0) >= 0)
+ feature |= PTRACE_SUPPORTS_PTMULTI;
ptrace(PTRACE_KILL,pid,0,0);
/* eliminate zombie */
if(waitpid(pid, &status, WUNTRACED) < 0)
@@ -392,10 +410,11 @@
static int __init check_sysptvm(void)
{
- int feature=test_ptrace_sysptvm();
+ int feature=test_ptrace_sysptvm_and_ptmulti();
+ int rv=0;
non_fatal("Checking ptrace new tags for syscall emulation...");
- if (feature==PTRACE_SYSCALL_SKIPCALL) {
+ if ((feature & ~PTRACE_SUPPORTS_PTMULTI)==PTRACE_SYSCALL_SKIPCALL) {
sysptvm_supported=1;
non_fatal("OK");
if (!force_sysptvm_disabled)
@@ -403,10 +422,21 @@
else
non_fatal(" (disabled)");
non_fatal("\n");
- return 1;
+ rv=1;
} else
non_fatal("unsupported\n");
- return 0;
+ non_fatal("Checking ptrace multi speedup...");
+ if (feature & PTRACE_SUPPORTS_PTMULTI) {
+ sysptmulti_supported=1;
+ non_fatal("OK");
+ if (force_sysptmulti_disabled)
+ non_fatal(" (disabled)");
+ else
+ set_using_sysptmulti(1);
+ non_fatal("\n");
+ } else
+ non_fatal("unsupported\n");
+ return rv;
}
static void __init check_ptrace(void)
--
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