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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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18ad51dd34
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: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
46 lines
1.2 KiB
ArmAsm
46 lines
1.2 KiB
ArmAsm
/*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright (C) IBM Corporation, 2012
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*
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* Author: Anton Blanchard <anton@au.ibm.com>
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*/
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#include <asm/ppc_asm.h>
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#include <asm/vdso.h>
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.text
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/*
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* Exact prototype of getcpu
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*
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* int __kernel_getcpu(unsigned *cpu, unsigned *node);
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*
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*/
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V_FUNCTION_BEGIN(__kernel_getcpu)
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.cfi_startproc
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mfspr r5,SPRN_USPRG3
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cmpdi cr0,r3,0
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cmpdi cr1,r4,0
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clrlwi r6,r5,16
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rlwinm r7,r5,16,31-15,31-0
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beq cr0,1f
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stw r6,0(r3)
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1: beq cr1,2f
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stw r7,0(r4)
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2: crclr cr0*4+so
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li r3,0 /* always success */
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blr
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.cfi_endproc
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V_FUNCTION_END(__kernel_getcpu)
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