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linux/arch/powerpc/lib/copyuser_power7.S
Anton Blanchard a66086b819 powerpc: POWER7 optimised copy_to_user/copy_from_user using VMX 
Implement a POWER7 optimised copy_to_user/copy_from_user using VMX.
For large aligned copies this new loop is over 10% faster, and for
large unaligned copies it is over 200% faster.

If we take a fault we fall back to the old version, this keeps
things relatively simple and easy to verify.

On POWER7 unaligned stores rarely slow down - they only flush when
a store crosses a 4KB page boundary. Furthermore this flush is
handled completely in hardware and should be 20-30 cycles.

Unaligned loads on the other hand flush much more often - whenever
crossing a 128 byte cache line, or a 32 byte sector if either sector
is an L1 miss.

Considering this information we really want to get the loads aligned
and not worry about the alignment of the stores. Microbenchmarks
confirm that this approach is much faster than the current unaligned
copy loop that uses shifts and rotates to ensure both loads and
stores are aligned.

We also want to try and do the stores in cacheline aligned, cacheline
sized chunks. If the store queue is unable to merge an entire
cacheline of stores then the L2 cache will have to do a
read/modify/write. Even worse, we will serialise this with the stores
in the next iteration of the copy loop since both iterations hit
the same cacheline.

Based on this, the new loop does the following things:

1 - 127 bytes
Get the source 8 byte aligned and use 8 byte loads and stores. Pretty
boring and similar to how the current loop works.

128 - 4095 bytes
Get the source 8 byte aligned and use 8 byte loads and stores,
1 cacheline at a time. We aren't doing the stores in cacheline
aligned chunks so we will potentially serialise once per cacheline.
Even so it is much better than the loop we have today.

4096 - bytes
If both source and destination have the same alignment get them both
16 byte aligned, then get the destination cacheline aligned. Do
cacheline sized loads and stores using VMX.

If source and destination do not have the same alignment, we get the
destination cacheline aligned, and use permute to do aligned loads.

In both cases the VMX loop should be optimal - we always do aligned
loads and stores and are always doing stores in cacheline aligned,
cacheline sized chunks.

To be able to use VMX we must be careful about interrupts and
sleeping. We don't use the VMX loop when in an interrupt (which should
be rare anyway) and we wrap the VMX loop in disable/enable_pagefault
and fall back to the existing copy_tofrom_user loop if we do need to
sleep.

The VMX breakpoint of 4096 bytes was chosen using this microbenchmark:

http://ozlabs.org/~anton/junkcode/copy_to_user.c

Since we are using VMX and there is a cost to saving and restoring
the user VMX state there are two broad cases we need to benchmark:

- Best case - userspace never uses VMX

- Worst case - userspace always uses VMX

In reality a userspace process will sit somewhere between these two
extremes. Since we need to test both aligned and unaligned copies we
end up with 4 combinations. The point at which the VMX loop begins to
win is:

0% VMX
aligned		2048 bytes
unaligned	2048 bytes

100% VMX
aligned		16384 bytes
unaligned	8192 bytes

Considering this is a microbenchmark, the data is hot in cache and
the VMX loop has better store queue merging properties we set the
breakpoint to 4096 bytes, a little below the unaligned breakpoints.

Some future optimisations we can look at:

- Looking at the perf data, a significant part of the cost when a
  task is always using VMX is the extra exception we take to restore
  the VMX state. As such we should do something similar to the x86
  optimisation that restores FPU state for heavy users. ie:

        /*
         * If the task has used fpu the last 5 timeslices, just do a full
         * restore of the math state immediately to avoid the trap; the
         * chances of needing FPU soon are obviously high now
         */
        preload_fpu = tsk_used_math(next_p) && next_p->fpu_counter > 5;

  and

        /*
         * fpu_counter contains the number of consecutive context switches
         * that the FPU is used. If this is over a threshold, the lazy fpu
         * saving becomes unlazy to save the trap. This is an unsigned char
         * so that after 256 times the counter wraps and the behavior turns
         * lazy again; this to deal with bursty apps that only use FPU for
         * a short time
         */

- We could create a paca bit to mirror the VMX enabled MSR bit and check
  that first, avoiding multiple calls to calling enable_kernel_altivec.
  That should help with iovec based system calls like readv.

- We could have two VMX breakpoints, one for when we know the user VMX
  state is loaded into the registers and one when it isn't. This could
  be a second bit in the paca so we can calculate the break points quickly.

- One suggestion from Ben was to save and restore the VSX registers
  we use inline instead of using enable_kernel_altivec.

[BenH: Fixed a problem with preempt and fixed build without CONFIG_ALTIVEC]

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2011-12-19 14:40:40 +11:00

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/*
* 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, 2011
*
* Author: Anton Blanchard <anton@au.ibm.com>
*/
#include <asm/ppc_asm.h>
#define STACKFRAMESIZE 256
#define STK_REG(i) (112 + ((i)-14)*8)
.macro err1
100:
.section __ex_table,"a"
.align 3
.llong 100b,.Ldo_err1
.previous
.endm
.macro err2
200:
.section __ex_table,"a"
.align 3
.llong 200b,.Ldo_err2
.previous
.endm
#ifdef CONFIG_ALTIVEC
.macro err3
300:
.section __ex_table,"a"
.align 3
.llong 300b,.Ldo_err3
.previous
.endm
.macro err4
400:
.section __ex_table,"a"
.align 3
.llong 400b,.Ldo_err4
.previous
.endm
.Ldo_err4:
ld r16,STK_REG(r16)(r1)
ld r15,STK_REG(r15)(r1)
ld r14,STK_REG(r14)(r1)
.Ldo_err3:
bl .exit_vmx_copy
ld r0,STACKFRAMESIZE+16(r1)
mtlr r0
b .Lexit
#endif /* CONFIG_ALTIVEC */
.Ldo_err2:
ld r22,STK_REG(r22)(r1)
ld r21,STK_REG(r21)(r1)
ld r20,STK_REG(r20)(r1)
ld r19,STK_REG(r19)(r1)
ld r18,STK_REG(r18)(r1)
ld r17,STK_REG(r17)(r1)
ld r16,STK_REG(r16)(r1)
ld r15,STK_REG(r15)(r1)
ld r14,STK_REG(r14)(r1)
.Lexit:
addi r1,r1,STACKFRAMESIZE
.Ldo_err1:
ld r3,48(r1)
ld r4,56(r1)
ld r5,64(r1)
b __copy_tofrom_user_base
_GLOBAL(__copy_tofrom_user_power7)
#ifdef CONFIG_ALTIVEC
cmpldi r5,16
cmpldi cr1,r5,4096
std r3,48(r1)
std r4,56(r1)
std r5,64(r1)
blt .Lshort_copy
bgt cr1,.Lvmx_copy
#else
cmpldi r5,16
std r3,48(r1)
std r4,56(r1)
std r5,64(r1)
blt .Lshort_copy
#endif
.Lnonvmx_copy:
/* Get the source 8B aligned */
neg r6,r4
mtocrf 0x01,r6
clrldi r6,r6,(64-3)
bf cr7*4+3,1f
err1; lbz r0,0(r4)
addi r4,r4,1
err1; stb r0,0(r3)
addi r3,r3,1
1: bf cr7*4+2,2f
err1; lhz r0,0(r4)
addi r4,r4,2
err1; sth r0,0(r3)
addi r3,r3,2
2: bf cr7*4+1,3f
err1; lwz r0,0(r4)
addi r4,r4,4
err1; stw r0,0(r3)
addi r3,r3,4
3: sub r5,r5,r6
cmpldi r5,128
blt 5f
mflr r0
stdu r1,-STACKFRAMESIZE(r1)
std r14,STK_REG(r14)(r1)
std r15,STK_REG(r15)(r1)
std r16,STK_REG(r16)(r1)
std r17,STK_REG(r17)(r1)
std r18,STK_REG(r18)(r1)
std r19,STK_REG(r19)(r1)
std r20,STK_REG(r20)(r1)
std r21,STK_REG(r21)(r1)
std r22,STK_REG(r22)(r1)
std r0,STACKFRAMESIZE+16(r1)
srdi r6,r5,7
mtctr r6
/* Now do cacheline (128B) sized loads and stores. */
.align 5
4:
err2; ld r0,0(r4)
err2; ld r6,8(r4)
err2; ld r7,16(r4)
err2; ld r8,24(r4)
err2; ld r9,32(r4)
err2; ld r10,40(r4)
err2; ld r11,48(r4)
err2; ld r12,56(r4)
err2; ld r14,64(r4)
err2; ld r15,72(r4)
err2; ld r16,80(r4)
err2; ld r17,88(r4)
err2; ld r18,96(r4)
err2; ld r19,104(r4)
err2; ld r20,112(r4)
err2; ld r21,120(r4)
addi r4,r4,128
err2; std r0,0(r3)
err2; std r6,8(r3)
err2; std r7,16(r3)
err2; std r8,24(r3)
err2; std r9,32(r3)
err2; std r10,40(r3)
err2; std r11,48(r3)
err2; std r12,56(r3)
err2; std r14,64(r3)
err2; std r15,72(r3)
err2; std r16,80(r3)
err2; std r17,88(r3)
err2; std r18,96(r3)
err2; std r19,104(r3)
err2; std r20,112(r3)
err2; std r21,120(r3)
addi r3,r3,128
bdnz 4b
clrldi r5,r5,(64-7)
ld r14,STK_REG(r14)(r1)
ld r15,STK_REG(r15)(r1)
ld r16,STK_REG(r16)(r1)
ld r17,STK_REG(r17)(r1)
ld r18,STK_REG(r18)(r1)
ld r19,STK_REG(r19)(r1)
ld r20,STK_REG(r20)(r1)
ld r21,STK_REG(r21)(r1)
ld r22,STK_REG(r22)(r1)
addi r1,r1,STACKFRAMESIZE
/* Up to 127B to go */
5: srdi r6,r5,4
mtocrf 0x01,r6
6: bf cr7*4+1,7f
err1; ld r0,0(r4)
err1; ld r6,8(r4)
err1; ld r7,16(r4)
err1; ld r8,24(r4)
err1; ld r9,32(r4)
err1; ld r10,40(r4)
err1; ld r11,48(r4)
err1; ld r12,56(r4)
addi r4,r4,64
err1; std r0,0(r3)
err1; std r6,8(r3)
err1; std r7,16(r3)
err1; std r8,24(r3)
err1; std r9,32(r3)
err1; std r10,40(r3)
err1; std r11,48(r3)
err1; std r12,56(r3)
addi r3,r3,64
/* Up to 63B to go */
7: bf cr7*4+2,8f
err1; ld r0,0(r4)
err1; ld r6,8(r4)
err1; ld r7,16(r4)
err1; ld r8,24(r4)
addi r4,r4,32
err1; std r0,0(r3)
err1; std r6,8(r3)
err1; std r7,16(r3)
err1; std r8,24(r3)
addi r3,r3,32
/* Up to 31B to go */
8: bf cr7*4+3,9f
err1; ld r0,0(r4)
err1; ld r6,8(r4)
addi r4,r4,16
err1; std r0,0(r3)
err1; std r6,8(r3)
addi r3,r3,16
9: clrldi r5,r5,(64-4)
/* Up to 15B to go */
.Lshort_copy:
mtocrf 0x01,r5
bf cr7*4+0,12f
err1; lwz r0,0(r4) /* Less chance of a reject with word ops */
err1; lwz r6,4(r4)
addi r4,r4,8
err1; stw r0,0(r3)
err1; stw r6,4(r3)
addi r3,r3,8
12: bf cr7*4+1,13f
err1; lwz r0,0(r4)
addi r4,r4,4
err1; stw r0,0(r3)
addi r3,r3,4
13: bf cr7*4+2,14f
err1; lhz r0,0(r4)
addi r4,r4,2
err1; sth r0,0(r3)
addi r3,r3,2
14: bf cr7*4+3,15f
err1; lbz r0,0(r4)
err1; stb r0,0(r3)
15: li r3,0
blr
.Lunwind_stack_nonvmx_copy:
addi r1,r1,STACKFRAMESIZE
b .Lnonvmx_copy
#ifdef CONFIG_ALTIVEC
.Lvmx_copy:
mflr r0
std r0,16(r1)
stdu r1,-STACKFRAMESIZE(r1)
bl .enter_vmx_copy
cmpwi r3,0
ld r0,STACKFRAMESIZE+16(r1)
ld r3,STACKFRAMESIZE+48(r1)
ld r4,STACKFRAMESIZE+56(r1)
ld r5,STACKFRAMESIZE+64(r1)
mtlr r0
beq .Lunwind_stack_nonvmx_copy
/*
* If source and destination are not relatively aligned we use a
* slower permute loop.
*/
xor r6,r4,r3
rldicl. r6,r6,0,(64-4)
bne .Lvmx_unaligned_copy
/* Get the destination 16B aligned */
neg r6,r3
mtocrf 0x01,r6
clrldi r6,r6,(64-4)
bf cr7*4+3,1f
err3; lbz r0,0(r4)
addi r4,r4,1
err3; stb r0,0(r3)
addi r3,r3,1
1: bf cr7*4+2,2f
err3; lhz r0,0(r4)
addi r4,r4,2
err3; sth r0,0(r3)
addi r3,r3,2
2: bf cr7*4+1,3f
err3; lwz r0,0(r4)
addi r4,r4,4
err3; stw r0,0(r3)
addi r3,r3,4
3: bf cr7*4+0,4f
err3; ld r0,0(r4)
addi r4,r4,8
err3; std r0,0(r3)
addi r3,r3,8
4: sub r5,r5,r6
/* Get the desination 128B aligned */
neg r6,r3
srdi r7,r6,4
mtocrf 0x01,r7
clrldi r6,r6,(64-7)
li r9,16
li r10,32
li r11,48
bf cr7*4+3,5f
err3; lvx vr1,r0,r4
addi r4,r4,16
err3; stvx vr1,r0,r3
addi r3,r3,16
5: bf cr7*4+2,6f
err3; lvx vr1,r0,r4
err3; lvx vr0,r4,r9
addi r4,r4,32
err3; stvx vr1,r0,r3
err3; stvx vr0,r3,r9
addi r3,r3,32
6: bf cr7*4+1,7f
err3; lvx vr3,r0,r4
err3; lvx vr2,r4,r9
err3; lvx vr1,r4,r10
err3; lvx vr0,r4,r11
addi r4,r4,64
err3; stvx vr3,r0,r3
err3; stvx vr2,r3,r9
err3; stvx vr1,r3,r10
err3; stvx vr0,r3,r11
addi r3,r3,64
7: sub r5,r5,r6
srdi r6,r5,7
std r14,STK_REG(r14)(r1)
std r15,STK_REG(r15)(r1)
std r16,STK_REG(r16)(r1)
li r12,64
li r14,80
li r15,96
li r16,112
mtctr r6
/*
* Now do cacheline sized loads and stores. By this stage the
* cacheline stores are also cacheline aligned.
*/
.align 5
8:
err4; lvx vr7,r0,r4
err4; lvx vr6,r4,r9
err4; lvx vr5,r4,r10
err4; lvx vr4,r4,r11
err4; lvx vr3,r4,r12
err4; lvx vr2,r4,r14
err4; lvx vr1,r4,r15
err4; lvx vr0,r4,r16
addi r4,r4,128
err4; stvx vr7,r0,r3
err4; stvx vr6,r3,r9
err4; stvx vr5,r3,r10
err4; stvx vr4,r3,r11
err4; stvx vr3,r3,r12
err4; stvx vr2,r3,r14
err4; stvx vr1,r3,r15
err4; stvx vr0,r3,r16
addi r3,r3,128
bdnz 8b
ld r14,STK_REG(r14)(r1)
ld r15,STK_REG(r15)(r1)
ld r16,STK_REG(r16)(r1)
/* Up to 127B to go */
clrldi r5,r5,(64-7)
srdi r6,r5,4
mtocrf 0x01,r6
bf cr7*4+1,9f
err3; lvx vr3,r0,r4
err3; lvx vr2,r4,r9
err3; lvx vr1,r4,r10
err3; lvx vr0,r4,r11
addi r4,r4,64
err3; stvx vr3,r0,r3
err3; stvx vr2,r3,r9
err3; stvx vr1,r3,r10
err3; stvx vr0,r3,r11
addi r3,r3,64
9: bf cr7*4+2,10f
err3; lvx vr1,r0,r4
err3; lvx vr0,r4,r9
addi r4,r4,32
err3; stvx vr1,r0,r3
err3; stvx vr0,r3,r9
addi r3,r3,32
10: bf cr7*4+3,11f
err3; lvx vr1,r0,r4
addi r4,r4,16
err3; stvx vr1,r0,r3
addi r3,r3,16
/* Up to 15B to go */
11: clrldi r5,r5,(64-4)
mtocrf 0x01,r5
bf cr7*4+0,12f
err3; ld r0,0(r4)
addi r4,r4,8
err3; std r0,0(r3)
addi r3,r3,8
12: bf cr7*4+1,13f
err3; lwz r0,0(r4)
addi r4,r4,4
err3; stw r0,0(r3)
addi r3,r3,4
13: bf cr7*4+2,14f
err3; lhz r0,0(r4)
addi r4,r4,2
err3; sth r0,0(r3)
addi r3,r3,2
14: bf cr7*4+3,15f
err3; lbz r0,0(r4)
err3; stb r0,0(r3)
15: addi r1,r1,STACKFRAMESIZE
b .exit_vmx_copy /* tail call optimise */
.Lvmx_unaligned_copy:
/* Get the destination 16B aligned */
neg r6,r3
mtocrf 0x01,r6
clrldi r6,r6,(64-4)
bf cr7*4+3,1f
err3; lbz r0,0(r4)
addi r4,r4,1
err3; stb r0,0(r3)
addi r3,r3,1
1: bf cr7*4+2,2f
err3; lhz r0,0(r4)
addi r4,r4,2
err3; sth r0,0(r3)
addi r3,r3,2
2: bf cr7*4+1,3f
err3; lwz r0,0(r4)
addi r4,r4,4
err3; stw r0,0(r3)
addi r3,r3,4
3: bf cr7*4+0,4f
err3; lwz r0,0(r4) /* Less chance of a reject with word ops */
err3; lwz r7,4(r4)
addi r4,r4,8
err3; stw r0,0(r3)
err3; stw r7,4(r3)
addi r3,r3,8
4: sub r5,r5,r6
/* Get the desination 128B aligned */
neg r6,r3
srdi r7,r6,4
mtocrf 0x01,r7
clrldi r6,r6,(64-7)
li r9,16
li r10,32
li r11,48
lvsl vr16,0,r4 /* Setup permute control vector */
err3; lvx vr0,0,r4
addi r4,r4,16
bf cr7*4+3,5f
err3; lvx vr1,r0,r4
vperm vr8,vr0,vr1,vr16
addi r4,r4,16
err3; stvx vr8,r0,r3
addi r3,r3,16
vor vr0,vr1,vr1
5: bf cr7*4+2,6f
err3; lvx vr1,r0,r4
vperm vr8,vr0,vr1,vr16
err3; lvx vr0,r4,r9
vperm vr9,vr1,vr0,vr16
addi r4,r4,32
err3; stvx vr8,r0,r3
err3; stvx vr9,r3,r9
addi r3,r3,32
6: bf cr7*4+1,7f
err3; lvx vr3,r0,r4
vperm vr8,vr0,vr3,vr16
err3; lvx vr2,r4,r9
vperm vr9,vr3,vr2,vr16
err3; lvx vr1,r4,r10
vperm vr10,vr2,vr1,vr16
err3; lvx vr0,r4,r11
vperm vr11,vr1,vr0,vr16
addi r4,r4,64
err3; stvx vr8,r0,r3
err3; stvx vr9,r3,r9
err3; stvx vr10,r3,r10
err3; stvx vr11,r3,r11
addi r3,r3,64
7: sub r5,r5,r6
srdi r6,r5,7
std r14,STK_REG(r14)(r1)
std r15,STK_REG(r15)(r1)
std r16,STK_REG(r16)(r1)
li r12,64
li r14,80
li r15,96
li r16,112
mtctr r6
/*
* Now do cacheline sized loads and stores. By this stage the
* cacheline stores are also cacheline aligned.
*/
.align 5
8:
err4; lvx vr7,r0,r4
vperm vr8,vr0,vr7,vr16
err4; lvx vr6,r4,r9
vperm vr9,vr7,vr6,vr16
err4; lvx vr5,r4,r10
vperm vr10,vr6,vr5,vr16
err4; lvx vr4,r4,r11
vperm vr11,vr5,vr4,vr16
err4; lvx vr3,r4,r12
vperm vr12,vr4,vr3,vr16
err4; lvx vr2,r4,r14
vperm vr13,vr3,vr2,vr16
err4; lvx vr1,r4,r15
vperm vr14,vr2,vr1,vr16
err4; lvx vr0,r4,r16
vperm vr15,vr1,vr0,vr16
addi r4,r4,128
err4; stvx vr8,r0,r3
err4; stvx vr9,r3,r9
err4; stvx vr10,r3,r10
err4; stvx vr11,r3,r11
err4; stvx vr12,r3,r12
err4; stvx vr13,r3,r14
err4; stvx vr14,r3,r15
err4; stvx vr15,r3,r16
addi r3,r3,128
bdnz 8b
ld r14,STK_REG(r14)(r1)
ld r15,STK_REG(r15)(r1)
ld r16,STK_REG(r16)(r1)
/* Up to 127B to go */
clrldi r5,r5,(64-7)
srdi r6,r5,4
mtocrf 0x01,r6
bf cr7*4+1,9f
err3; lvx vr3,r0,r4
vperm vr8,vr0,vr3,vr16
err3; lvx vr2,r4,r9
vperm vr9,vr3,vr2,vr16
err3; lvx vr1,r4,r10
vperm vr10,vr2,vr1,vr16
err3; lvx vr0,r4,r11
vperm vr11,vr1,vr0,vr16
addi r4,r4,64
err3; stvx vr8,r0,r3
err3; stvx vr9,r3,r9
err3; stvx vr10,r3,r10
err3; stvx vr11,r3,r11
addi r3,r3,64
9: bf cr7*4+2,10f
err3; lvx vr1,r0,r4
vperm vr8,vr0,vr1,vr16
err3; lvx vr0,r4,r9
vperm vr9,vr1,vr0,vr16
addi r4,r4,32
err3; stvx vr8,r0,r3
err3; stvx vr9,r3,r9
addi r3,r3,32
10: bf cr7*4+3,11f
err3; lvx vr1,r0,r4
vperm vr8,vr0,vr1,vr16
addi r4,r4,16
err3; stvx vr8,r0,r3
addi r3,r3,16
/* Up to 15B to go */
11: clrldi r5,r5,(64-4)
addi r4,r4,-16 /* Unwind the +16 load offset */
mtocrf 0x01,r5
bf cr7*4+0,12f
err3; lwz r0,0(r4) /* Less chance of a reject with word ops */
err3; lwz r6,4(r4)
addi r4,r4,8
err3; stw r0,0(r3)
err3; stw r6,4(r3)
addi r3,r3,8
12: bf cr7*4+1,13f
err3; lwz r0,0(r4)
addi r4,r4,4
err3; stw r0,0(r3)
addi r3,r3,4
13: bf cr7*4+2,14f
err3; lhz r0,0(r4)
addi r4,r4,2
err3; sth r0,0(r3)
addi r3,r3,2
14: bf cr7*4+3,15f
err3; lbz r0,0(r4)
err3; stb r0,0(r3)
15: addi r1,r1,STACKFRAMESIZE
b .exit_vmx_copy /* tail call optimise */
#endif /* CONFiG_ALTIVEC */
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