[PATCH] x86: Add portable getcpu call

For NUMA optimization and some other algorithms it is useful to have a fast to get the current CPU and node numbers in user space. x86-64 added a fast way to do this in a vsyscall. This adds a generic syscall for other architectures to make it a generic portable facility. I expect some of them will also implement it as a faster vsyscall. The cache is an optimization for the x86-64 vsyscall optimization. Since what the syscall returns is an approximation anyways and user space often wants very fast results it can be cached for some time. The norma methods to get this information in user space are relatively slow The vsyscall is in a better position to manage the cache because it has direct access to a fast time stamp (jiffies). For the generic syscall optimization it doesn't help much, but enforce a valid argument to keep programs portable I only added an i386 syscall entry for now. Other architectures can follow as needed. AK: Also added some cleanups from Andrew Morton Signed-off-by: Andi Kleen <ak@suse.de>

[PATCH] x86: Add portable getcpu call
For NUMA optimization and some other algorithms it is useful to have a fast to get the current CPU and node numbers in user space. x86-64 added a fast way to do this in a vsyscall. This adds a generic syscall for other architectures to make it a generic portable facility. I expect some of them will also implement it as a faster vsyscall. The cache is an optimization for the x86-64 vsyscall optimization. Since what the syscall returns is an approximation anyways and user space often wants very fast results it can be cached for some time. The norma methods to get this information in user space are relatively slow The vsyscall is in a better position to manage the cache because it has direct access to a fast time stamp (jiffies). For the generic syscall optimization it doesn't help much, but enforce a valid argument to keep programs portable I only added an i386 syscall entry for now. Other architectures can follow as needed. AK: Also added some cleanups from Andrew Morton Signed-off-by: Andi Kleen <ak@suse.de>
Andi Kleen · Andi Kleen
1 parent c08c820508
Showing 5 changed files with 37 additions and 1 deletions Side-by-side Diff
arch/i386/kernel/syscall_table.S
arch/x86_64/ia32/ia32entry.S
include/asm-i386/unistd.h
include/linux/syscalls.h
kernel/sys.c
@@ -317,4 +317,5 @@
 	.long sys_tee			/* 315 */
 	.long sys_vmsplice
 	.long sys_move_pages
+	.long sys_getcpu
@@ -713,5 +713,6 @@
 	.quad sys_tee
 	.quad compat_sys_vmsplice
 	.quad compat_sys_move_pages
+	.quad sys_getcpu
 ia32_syscall_end:		
@@ -323,10 +323,11 @@
 #define __NR_tee		315
 #define __NR_vmsplice		316
 #define __NR_move_pages		317
+#define __NR_getcpu		318
  
 #ifdef __KERNEL__
  
-#define NR_syscalls 318
+#define NR_syscalls 319
  
 /*
  * user-visible error numbers are in the range -1 - -128: see
@@ -53,6 +53,7 @@
 struct compat_stat;
 struct compat_timeval;
 struct robust_list_head;
+struct getcpu_cache;
  
 #include <linux/types.h>
 #include <linux/aio_abi.h>
@@ -596,6 +597,7 @@
 				    size_t __user *len_ptr);
 asmlinkage long sys_set_robust_list(struct robust_list_head __user *head,
 				    size_t len);
+asmlinkage long sys_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *cache);
  
 #endif
@@ -28,6 +28,7 @@
 #include <linux/tty.h>
 #include <linux/signal.h>
 #include <linux/cn_proc.h>
+#include <linux/getcpu.h>
  
 #include <linux/compat.h>
 #include <linux/syscalls.h>
@@ -2061,5 +2062,35 @@
 			break;
 	}
 	return error;
+}
+
+asmlinkage long sys_getcpu(unsigned __user *cpup, unsigned __user *nodep,
+	   		   struct getcpu_cache __user *cache)
+{
+	int err = 0;
+	int cpu = raw_smp_processor_id();
+	if (cpup)
+		err |= put_user(cpu, cpup);
+	if (nodep)
+		err |= put_user(cpu_to_node(cpu), nodep);
+	if (cache) {
+		/*
+		 * The cache is not needed for this implementation,
+		 * but make sure user programs pass something
+		 * valid. vsyscall implementations can instead make
+		 * good use of the cache. Only use t0 and t1 because
+		 * these are available in both 32bit and 64bit ABI (no
+		 * need for a compat_getcpu). 32bit has enough
+		 * padding
+		 */
+		unsigned long t0, t1;
+		get_user(t0, &cache->t0);
+		get_user(t1, &cache->t1);
+		t0++;
+		t1++;
+		put_user(t0, &cache->t0);
+		put_user(t1, &cache->t1);
+	}
+	return err ? -EFAULT : 0;
 }
...	...	@@ -317,4 +317,5 @@
317	317	.long sys_tee /* 315 */
318	318	.long sys_vmsplice
319	319	.long sys_move_pages
	320	+ .long sys_getcpu
...	...	@@ -713,5 +713,6 @@
713	713	.quad sys_tee
714	714	.quad compat_sys_vmsplice
715	715	.quad compat_sys_move_pages
	716	+ .quad sys_getcpu
716	717	ia32_syscall_end:
...	...	@@ -323,10 +323,11 @@
323	323	#define __NR_tee 315
324	324	#define __NR_vmsplice 316
325	325	#define __NR_move_pages 317
	326	+#define __NR_getcpu 318
326	327
327	328	#ifdef __KERNEL__
328	329
329		-#define NR_syscalls 318
	330	+#define NR_syscalls 319
330	331
331	332	/*
332	333	* user-visible error numbers are in the range -1 - -128: see
...	...	@@ -53,6 +53,7 @@
53	53	struct compat_stat;
54	54	struct compat_timeval;
55	55	struct robust_list_head;
	56	+struct getcpu_cache;
56	57
57	58	#include <linux/types.h>
58	59	#include <linux/aio_abi.h>
...	...	@@ -596,6 +597,7 @@
596	597	size_t __user *len_ptr);
597	598	asmlinkage long sys_set_robust_list(struct robust_list_head __user *head,
598	599	size_t len);
	600	+asmlinkage long sys_getcpu(unsigned cpu, unsigned node, struct getcpu_cache *cache);
599	601
600	602	#endif
...	...	@@ -28,6 +28,7 @@
28	28	#include <linux/tty.h>
29	29	#include <linux/signal.h>
30	30	#include <linux/cn_proc.h>
	31	+#include <linux/getcpu.h>
31	32
32	33	#include <linux/compat.h>
33	34	#include <linux/syscalls.h>
...	...	@@ -2061,5 +2062,35 @@
2061	2062	break;
2062	2063	}
2063	2064	return error;
	2065	+}
	2066	+
	2067	+asmlinkage long sys_getcpu(unsigned __user cpup, unsigned __user nodep,
	2068	+ struct getcpu_cache __user *cache)
	2069	+{
	2070	+ int err = 0;
	2071	+ int cpu = raw_smp_processor_id();
	2072	+ if (cpup)
	2073	+ err \|= put_user(cpu, cpup);
	2074	+ if (nodep)
	2075	+ err \|= put_user(cpu_to_node(cpu), nodep);
	2076	+ if (cache) {
	2077	+ /*
	2078	+ * The cache is not needed for this implementation,
	2079	+ * but make sure user programs pass something
	2080	+ * valid. vsyscall implementations can instead make
	2081	+ * good use of the cache. Only use t0 and t1 because
	2082	+ * these are available in both 32bit and 64bit ABI (no
	2083	+ * need for a compat_getcpu). 32bit has enough
	2084	+ * padding
	2085	+ */
	2086	+ unsigned long t0, t1;
	2087	+ get_user(t0, &cache->t0);
	2088	+ get_user(t1, &cache->t1);
	2089	+ t0++;
	2090	+ t1++;
	2091	+ put_user(t0, &cache->t0);
	2092	+ put_user(t1, &cache->t1);
	2093	+ }
	2094	+ return err ? -EFAULT : 0;
2064	2095	}