We had a request for a fast method of getting CPU and NUMA node IDs
from userspace. Ben suggested we use SPRG3 which is userspace
readable. This is a quick hack to try that out.
I have a glibc patch to implement sched_getcpu using this. Testing
on a POWER7:
baseline: 538 cycles
vdso: 30 cycles
Signed-off-by: Anton Blanchard <an...@samba.org>
---
Outstanding issues:
- Do we have any KVM issues?
- This will only work with 64 bit kernels for now, do we need to come up
with a scheme for 32 bit?
- Implement 32 bit userspace version (running on 64 bit kernels)
Index: linux-build/arch/powerpc/include/asm/reg.h
===================================================================
--- linux-build.orig/arch/powerpc/include/asm/reg.h 2012-06-25
10:05:52.193076424 +1000
+++ linux-build/arch/powerpc/include/asm/reg.h 2012-06-25 10:09:02.932316659
+1000
@@ -491,6 +491,7 @@
#define SPRN_SPRG1 0x111 /* Special Purpose Register General 1 */
#define SPRN_SPRG2 0x112 /* Special Purpose Register General 2 */
#define SPRN_SPRG3 0x113 /* Special Purpose Register General 3 */
+#define SPRN_USPRG3 0x103 /* SPRG3 userspace read */
#define SPRN_SPRG4 0x114 /* Special Purpose Register General 4 */
#define SPRN_SPRG5 0x115 /* Special Purpose Register General 5 */
#define SPRN_SPRG6 0x116 /* Special Purpose Register General 6 */
@@ -753,14 +754,14 @@
* 64-bit server:
* - SPRG0 unused (reserved for HV on Power4)
* - SPRG2 scratch for exception vectors
- * - SPRG3 unused (user visible)
+ * - SPRG3 CPU and NUMA node for VDSO getcpu (user visible)
* - HSPRG0 stores PACA in HV mode
* - HSPRG1 scratch for "HV" exceptions
*
* 64-bit embedded
* - SPRG0 generic exception scratch
* - SPRG2 TLB exception stack
- * - SPRG3 unused (user visible)
+ * - SPRG3 CPU and NUMA node for VDSO getcpu (user visible)
* - SPRG4 unused (user visible)
* - SPRG6 TLB miss scratch (user visible, sorry !)
* - SPRG7 critical exception scratch
Index: linux-build/arch/powerpc/kernel/vdso.c
===================================================================
--- linux-build.orig/arch/powerpc/kernel/vdso.c 2012-06-25 10:05:52.229077036
+1000
+++ linux-build/arch/powerpc/kernel/vdso.c 2012-06-25 10:12:50.256171890
+1000
@@ -706,6 +706,25 @@ static void __init vdso_setup_syscall_ma
}
}
+#ifdef CONFIG_PPC64
+int __cpuinit vdso_getcpu_init(void)
+{
+ unsigned long cpu, node;
+
+ /*
+ * SPRG3 contains the CPU in the bottom 32 bits and the NUMA node in the
+ * top 32 bits.
+ */
+ cpu = get_cpu();
+ node = cpu_to_node(cpu);
+ mtspr(SPRN_SPRG3, cpu | (node << 32));
+ put_cpu();
+
+ return 0;
+}
+/* We need to call this before SMP init */
+early_initcall(vdso_getcpu_init);
+#endif
static int __init vdso_init(void)
{
Index: linux-build/arch/powerpc/kernel/vdso64/Makefile
===================================================================
--- linux-build.orig/arch/powerpc/kernel/vdso64/Makefile 2012-06-25
10:05:52.209076696 +1000
+++ linux-build/arch/powerpc/kernel/vdso64/Makefile 2012-06-25
10:05:53.737102674 +1000
@@ -1,6 +1,6 @@
# List of files in the vdso, has to be asm only for now
-obj-vdso64 = sigtramp.o gettimeofday.o datapage.o cacheflush.o note.o
+obj-vdso64 = sigtramp.o gettimeofday.o datapage.o cacheflush.o note.o getcpu.o
# Build rules
Index: linux-build/arch/powerpc/kernel/vdso64/vdso64.lds.S
===================================================================
--- linux-build.orig/arch/powerpc/kernel/vdso64/vdso64.lds.S 2012-06-25
10:05:52.217076832 +1000
+++ linux-build/arch/powerpc/kernel/vdso64/vdso64.lds.S 2012-06-25
10:05:53.737102674 +1000
@@ -146,6 +146,7 @@ VERSION
__kernel_sync_dicache;
__kernel_sync_dicache_p5;
__kernel_sigtramp_rt64;
+ __kernel_getcpu;
local: *;
};
Index: linux-build/arch/powerpc/kernel/vdso64/getcpu.S
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-build/arch/powerpc/kernel/vdso64/getcpu.S 2012-06-25
10:09:11.796467121 +1000
@@ -0,0 +1,44 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2012
+ *
+ * Author: Anton Blanchard <an...@au.ibm.com>
+ */
+#include <asm/ppc_asm.h>
+#include <asm/vdso.h>
+
+ .text
+/*
+ * Exact prototype of getcpu
+ *
+ * int __kernel_getcpu(unsigned *cpu, unsigned *node);
+ *
+ */
+V_FUNCTION_BEGIN(__kernel_getcpu)
+ .cfi_startproc
+ mfspr r5,SPRN_USPRG3
+ cmpdi cr0,r3,0
+ cmpdi cr1,r4,0
+ srdi r6,r5,32
+ beq cr0,1f
+ stw r5,0(r3)
+1: beq cr1,2f
+ stw r6,0(r4)
+2: crclr cr0*4+so
+ li r3,0 /* always success */
+ blr
+ .cfi_endproc
+V_FUNCTION_END(__kernel_getcpu)
Index: linux-build/arch/powerpc/kernel/smp.c
===================================================================
--- linux-build.orig/arch/powerpc/kernel/smp.c 2012-06-25 10:05:52.197076492
+1000
+++ linux-build/arch/powerpc/kernel/smp.c 2012-06-25 10:13:54.897266908
+1000
@@ -48,6 +48,7 @@
#ifdef CONFIG_PPC64
#include <asm/paca.h>
#endif
+#include <asm/vdso.h>
#include <asm/debug.h>
#ifdef DEBUG
@@ -570,6 +571,8 @@ void __devinit start_secondary(void *unu
#ifdef CONFIG_PPC64
if (system_state == SYSTEM_RUNNING)
vdso_data->processorCount++;
+
+ vdso_getcpu_init();
#endif
ipi_call_lock();
notify_cpu_starting(cpu);
Index: linux-build/arch/powerpc/include/asm/vdso.h
===================================================================
--- linux-build.orig/arch/powerpc/include/asm/vdso.h 2012-06-25
10:05:52.181076220 +1000
+++ linux-build/arch/powerpc/include/asm/vdso.h 2012-06-25 10:05:53.737102674
+1000
@@ -22,6 +22,8 @@ extern unsigned long vdso64_rt_sigtramp;
extern unsigned long vdso32_sigtramp;
extern unsigned long vdso32_rt_sigtramp;
+int __cpuinit vdso_getcpu_init(void);
+
#else /* __ASSEMBLY__ */
#ifdef __VDSO64__
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