[PATCH for review] [27/145] x86_64: Add the vgetcpu vsyscall

Andi Kleen
2006-08-10T19:35:47Z

r

From: Vojtech Pavlik <vojtech@suse.cz>

This patch adds a vgetcpu vsyscall, which depending on the CPU RDTSCP
capability uses either the RDTSCP or CPUID to obtain a CPU and node
numbers and pass them to the program.

AK: Lots of changes over Vojtech's original code:
Better prototype for vgetcpu()
It's better to pass the cpu / node numbers as separate arguments
to avoid mistakes when going from SMP to NUMA.
Also add a fast time stamp based cache using a user supplied
argument to speed things more up.
Use fast method from Chuck Ebbert to retrieve node/cpu from
GDT limit instead of CPUID
Made sure RDTSCP init is always executed after node is known.
Drop printk

TBD benchmark LSL vs RDTSCP

Signed-off-by: Vojtech Pavlik <vojtech@suse.cz>
Signed-off-by: Andi Kleen <ak@suse.de>

---
arch/x86_64/kernel/head.S | 2
arch/x86_64/kernel/time.c | 13 +++--
arch/x86_64/kernel/vmlinux.lds.S | 3 +
arch/x86_64/kernel/vsyscall.c | 86 +++++++++++++++++++++++++++++++++++++--
include/asm-x86_64/segment.h | 5 +-
include/asm-x86_64/smp.h | 12 ++++-
include/asm-x86_64/vsyscall.h | 9 ++++
include/linux/getcpu.h | 16 +++++++
8 files changed, 131 insertions(+), 15 deletions(-)

Index: linux/arch/x86_64/kernel/vsyscall.c
===================================================================
--- linux.orig/arch/x86_64/kernel/vsyscall.c
+++ linux/arch/x86_64/kernel/vsyscall.c
@@ -26,6 +26,7 @@
#include <linux/seqlock.h>
#include <linux/jiffies.h>
#include <linux/sysctl.h>
+#include <linux/getcpu.h>

#include <asm/vsyscall.h>
#include <asm/pgtable.h>
@@ -33,11 +34,15 @@
#include <asm/fixmap.h>
#include <asm/errno.h>
#include <asm/io.h>
+#include <asm/segment.h>
+#include <asm/desc.h>
+#include <asm/topology.h>

#define __vsyscall(nr) __attribute__ ((unused,__section__(".vsyscall_" #nr)))

int __sysctl_vsyscall __section_sysctl_vsyscall = 1;
seqlock_t __xtime_lock __section_xtime_lock = SEQLOCK_UNLOCKED;
+int __vgetcpu_mode __section_vgetcpu_mode;

#include <asm/unistd.h>

@@ -127,9 +132,46 @@ time_t __vsyscall(1) vtime(time_t *t)
return __xtime.tv_sec;
}

-long __vsyscall(2) venosys_0(void)
-{
- return -ENOSYS;
+/* Fast way to get current CPU and node.
+ This helps to do per node and per CPU caches in user space.
+ The result is not guaranteed without CPU affinity, but usually
+ works out because the scheduler tries to keep a thread on the same
+ CPU.
+
+ tcache must point to a two element sized long array.
+ All arguments can be NULL. */
+long __vsyscall(2)
+vgetcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
+{
+ unsigned int dummy, p;
+ unsigned long j = 0;
+
+ /* Fast cache - only recompute value once per jiffies and avoid
+ relatively costly rdtscp/cpuid otherwise.
+ This works because the scheduler usually keeps the process
+ on the same CPU and this syscall doesn't guarantee its
+ results anyways.
+ We do this here because otherwise user space would do it on
+ its own in a likely inferior way (no access to jiffies).
+ If you don't like it pass NULL. */
+ if (tcache && tcache->t0 == (j = __jiffies)) {
+ p = tcache->t1;
+ } else if (__vgetcpu_mode == VGETCPU_RDTSCP) {
+ /* Load per CPU data from RDTSCP */
+ rdtscp(dummy, dummy, p);
+ } else {
+ /* Load per CPU data from GDT */
+ asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
+ }
+ if (tcache) {
+ tcache->t0 = j;
+ tcache->t1 = p;
+ }
+ if (cpu)
+ *cpu = p & 0xfff;
+ if (node)
+ *node = p >> 12;
+ return 0;
}

long __vsyscall(3) venosys_1(void)
@@ -200,6 +242,43 @@ static ctl_table kernel_root_table2[] =

#endif

+static void __cpuinit write_rdtscp_cb(void *info)
+{
+ write_rdtscp_aux((unsigned long)info);
+}
+
+void __cpuinit vsyscall_set_cpu(int cpu)
+{
+ unsigned long *d;
+ unsigned long node = 0;
+#ifdef CONFIG_NUMA
+ node = cpu_to_node[cpu];
+#endif
+ if (cpu_has(&cpu_data[cpu], X86_FEATURE_RDTSCP)) {
+ void *info = (void *)((node << 12) | cpu);
+ /* Can happen on preemptive kernel */
+ if (get_cpu() == cpu)
+ write_rdtscp_cb(info);
+#ifdef CONFIG_SMP
+ else {
+ /* the notifier is unfortunately not executed on the
+ target CPU */
+ smp_call_function_single(cpu,write_rdtscp_cb,info,0,1);
+ }
+#endif
+ put_cpu();
+ }
+
+ /* Store cpu number in limit so that it can be loaded quickly
+ in user space in vgetcpu.
+ 12 bits for the CPU and 8 bits for the node. */
+ d = (unsigned long *)(cpu_gdt(cpu) + GDT_ENTRY_PER_CPU);
+ *d = 0x0f40000000000ULL;
+ *d |= cpu;
+ *d |= (node & 0xf) << 12;
+ *d |= (node >> 4) << 48;
+}
+
static void __init map_vsyscall(void)
{
extern char __vsyscall_0;
@@ -214,6 +293,7 @@ static int __init vsyscall_init(void)
VSYSCALL_ADDR(__NR_vgettimeofday)));
BUG_ON((unsigned long) &vtime != VSYSCALL_ADDR(__NR_vtime));
BUG_ON((VSYSCALL_ADDR(0) != __fix_to_virt(VSYSCALL_FIRST_PAGE)));
+ BUG_ON((unsigned long) &vgetcpu != VSYSCALL_ADDR(__NR_vgetcpu));
map_vsyscall();
#ifdef CONFIG_SYSCTL
register_sysctl_table(kernel_root_table2, 0);
Index: linux/include/asm-x86_64/vsyscall.h
===================================================================
--- linux.orig/include/asm-x86_64/vsyscall.h
+++ linux/include/asm-x86_64/vsyscall.h
@@ -6,6 +6,7 @@
enum vsyscall_num {
__NR_vgettimeofday,
__NR_vtime,
+ __NR_vgetcpu,
};

#define VSYSCALL_START (-10UL << 20)
@@ -16,6 +17,7 @@ enum vsyscall_num {
#ifdef __KERNEL__

#define __section_vxtime __attribute__ ((unused, __section__ (".vxtime"), aligned(16)))
+#define __section_vgetcpu_mode __attribute__ ((unused, __section__ (".vgetcpu_mode"), aligned(16)))
#define __section_wall_jiffies __attribute__ ((unused, __section__ (".wall_jiffies"), aligned(16)))
#define __section_jiffies __attribute__ ((unused, __section__ (".jiffies"), aligned(16)))
#define __section_sys_tz __attribute__ ((unused, __section__ (".sys_tz"), aligned(16)))
@@ -27,6 +29,9 @@ enum vsyscall_num {
#define VXTIME_HPET 2
#define VXTIME_PMTMR 3

+#define VGETCPU_RDTSCP 1
+#define VGETCPU_LSL 2
+
struct vxtime_data {
long hpet_address; /* HPET base address */
int last;
@@ -41,6 +46,7 @@ struct vxtime_data {

/* vsyscall space (readonly) */
extern struct vxtime_data __vxtime;
+extern int __vgetcpu_mode;
extern struct timespec __xtime;
extern volatile unsigned long __jiffies;
extern unsigned long __wall_jiffies;
@@ -49,6 +55,7 @@ extern seqlock_t __xtime_lock;

/* kernel space (writeable) */
extern struct vxtime_data vxtime;
+extern int vgetcpu_mode;
extern unsigned long wall_jiffies;
extern struct timezone sys_tz;
extern int sysctl_vsyscall;
@@ -56,6 +63,8 @@ extern seqlock_t xtime_lock;

extern int sysctl_vsyscall;

+extern void vsyscall_set_cpu(int cpu);
+
#define ARCH_HAVE_XTIME_LOCK 1

#endif /* __KERNEL__ */
Index: linux/arch/x86_64/kernel/time.c
===================================================================
--- linux.orig/arch/x86_64/kernel/time.c
+++ linux/arch/x86_64/kernel/time.c
@@ -899,12 +899,8 @@ static int __cpuinit
time_cpu_notifier(struct notifier_block *nb, unsigned long action, void *hcpu)
{
unsigned cpu = (unsigned long) hcpu;
- if (action == CPU_ONLINE &&
- cpu_has(&cpu_data[cpu], X86_FEATURE_RDTSCP)) {
- unsigned p;
- p = smp_processor_id() | (cpu_to_node(smp_processor_id())<<12);
- write_rdtscp_aux(p);
- }
+ if (action == CPU_ONLINE)
+ vsyscall_set_cpu(cpu);
return NOTIFY_DONE;
}

@@ -993,6 +989,11 @@ void time_init_gtod(void)
if (unsynchronized_tsc())
notsc = 1;

+ if (cpu_has(&boot_cpu_data, X86_FEATURE_RDTSCP))
+ vgetcpu_mode = VGETCPU_RDTSCP;
+ else
+ vgetcpu_mode = VGETCPU_LSL;
+
if (vxtime.hpet_address && notsc) {
timetype = hpet_use_timer ? "HPET" : "PIT/HPET";
if (hpet_use_timer)
Index: linux/arch/x86_64/kernel/vmlinux.lds.S
===================================================================
--- linux.orig/arch/x86_64/kernel/vmlinux.lds.S
+++ linux/arch/x86_64/kernel/vmlinux.lds.S
@@ -99,6 +99,9 @@ SECTIONS
.vxtime : AT(VLOAD(.vxtime)) { *(.vxtime) }
vxtime = VVIRT(.vxtime);

+ .vgetcpu_mode : AT(VLOAD(.vgetcpu_mode)) { *(.vgetcpu_mode) }
+ vgetcpu_mode = VVIRT(.vgetcpu_mode);
+
.wall_jiffies : AT(VLOAD(.wall_jiffies)) { *(.wall_jiffies) }
wall_jiffies = VVIRT(.wall_jiffies);

Index: linux/arch/x86_64/kernel/head.S
===================================================================
--- linux.orig/arch/x86_64/kernel/head.S
+++ linux/arch/x86_64/kernel/head.S
@@ -370,7 +370,7 @@ ENTRY(cpu_gdt_table)
.quad 0,0 /* TSS */
.quad 0,0 /* LDT */
.quad 0,0,0 /* three TLS descriptors */
- .quad 0 /* unused */
+ .quad 0x0000f40000000000 /* node/CPU stored in limit */
gdt_end:
/* asm/segment.h:GDT_ENTRIES must match this */
/* This should be a multiple of the cache line size */
Index: linux/include/asm-x86_64/segment.h
===================================================================
--- linux.orig/include/asm-x86_64/segment.h
+++ linux/include/asm-x86_64/segment.h
@@ -20,15 +20,16 @@
#define __USER_CS 0x33 /* 6*8+3 */
#define __USER32_DS __USER_DS

-#define GDT_ENTRY_TLS 1
#define GDT_ENTRY_TSS 8 /* needs two entries */
#define GDT_ENTRY_LDT 10 /* needs two entries */
#define GDT_ENTRY_TLS_MIN 12
#define GDT_ENTRY_TLS_MAX 14
-/* 15 free */

#define GDT_ENTRY_TLS_ENTRIES 3

+#define GDT_ENTRY_PER_CPU 15 /* Abused to load per CPU data from limit */
+#define __PER_CPU_SEG (GDT_ENTRY_PER_CPU * 8 + 3)
+
/* TLS indexes for 64bit - hardcoded in arch_prctl */
#define FS_TLS 0
#define GS_TLS 1
Index: linux/include/asm-x86_64/smp.h
===================================================================
--- linux.orig/include/asm-x86_64/smp.h
+++ linux/include/asm-x86_64/smp.h
@@ -133,13 +133,19 @@ static __inline int logical_smp_processo
/* we don't want to mark this access volatile - bad code generation */
return GET_APIC_LOGICAL_ID(*(unsigned long *)(APIC_BASE+APIC_LDR));
}
-#endif

#ifdef CONFIG_SMP
#define cpu_physical_id(cpu) x86_cpu_to_apicid[cpu]
#else
#define cpu_physical_id(cpu) boot_cpu_id
-#endif
-
+static inline int smp_call_function_single(int cpuid, void (*func) (void *info),
+ void *info, int retry, int wait)
+{
+ /* Disable interrupts here? */
+ func(info);
+ return 0;
+}
+#endif /* !CONFIG_SMP */
+#endif /* !__ASSEMBLY */
#endif

Index: linux/include/linux/getcpu.h
===================================================================
--- /dev/null
+++ linux/include/linux/getcpu.h
@@ -0,0 +1,16 @@
+#ifndef _LINUX_GETCPU_H
+#define _LINUX_GETCPU_H 1
+
+/* Cache for getcpu() to speed it up. Results might be upto a jiffie
+ out of date, but will be faster.
+ User programs should not refer to the contents of this structure.
+ It is only a cache for vgetcpu(). It might change in future kernels.
+ The user program must store this information per thread (__thread)
+ If you want 100% accurate information pass NULL instead. */
+struct getcpu_cache {
+ unsigned long t0;
+ unsigned long t1;
+ unsigned long res[4];
+};
+
+#endif