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Commit 18ad51dd authored by Anton Blanchard's avatar Anton Blanchard Committed by Benjamin Herrenschmidt
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powerpc: Add VDSO version of getcpu 



We have a request for a fast method of getting CPU and NUMA node IDs
from userspace. This patch implements a getcpu VDSO function,
similar to x86.

Ben suggested we use SPRG3 which is userspace readable. SPRG3 can be
modified by a KVM guest, so we save the SPRG3 value in the paca and
restore it when transitioning from the guest to the host.

I have a glibc patch that implements sched_getcpu on top of this.
Testing on a POWER7:

baseline: 538 cycles
vdso:      30 cycles

Signed-off-by: default avatarAnton Blanchard <anton@samba.org>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent e6a74c6e

arch/powerpc/include/asm/kvm_book3s_asm.h

+1 −0
Original line number Diff line number Diff line
@@ -74,6 +74,7 @@ struct kvmppc_host_state { 
	ulong vmhandler;

	ulong scratch0;

	ulong scratch1;

	ulong sprg3;

	u8 in_guest;

	u8 restore_hid5;

	u8 napping;

arch/powerpc/include/asm/reg.h

+3 −2
Original line number Diff line number Diff line
@@ -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

arch/powerpc/include/asm/vdso.h

+2 −0
Original line number Diff line number Diff line
@@ -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__

arch/powerpc/kernel/asm-offsets.c

+1 −0
Original line number Diff line number Diff line
@@ -533,6 +533,7 @@ int main(void) 
	HSTATE_FIELD(HSTATE_VMHANDLER, vmhandler);

	HSTATE_FIELD(HSTATE_SCRATCH0, scratch0);

	HSTATE_FIELD(HSTATE_SCRATCH1, scratch1);

	HSTATE_FIELD(HSTATE_SPRG3, sprg3);

	HSTATE_FIELD(HSTATE_IN_GUEST, in_guest);

	HSTATE_FIELD(HSTATE_RESTORE_HID5, restore_hid5);

	HSTATE_FIELD(HSTATE_NAPPING, napping);

arch/powerpc/kernel/smp.c

+3 −0
Original line number Diff line number Diff line
@@ -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 *unused) 
#ifdef CONFIG_PPC64

	if (system_state == SYSTEM_RUNNING)

		vdso_data->processorCount++;



	vdso_getcpu_init();

#endif

	notify_cpu_starting(cpu);

	set_cpu_online(cpu, true);