Le 10/03/2023 à 19:26, Christophe Leroy a écrit :
>
>
> Le 09/03/2023 à 19:02, Hari Bathini a écrit :
>> patch_instruction() entails setting up pte, patching the instruction,
>> clearing the pte and flushing the tlb. If multiple instructions need
>> to be patched, every instruction would have to go through the above
>> drill unnecessarily. Instead, introduce function patch_instructions()
>> that patches multiple instructions at one go while setting up the pte,
>> clearing the pte and flushing the tlb only once per page range of
>> instructions. Observed ~5X improvement in speed of execution using
>> patch_instructions() over patch_instructions(), when more instructions
>> are to be patched.
>
> I get a 13% degradation on the time needed to activate ftrace on a
> powerpc 8xx.
>
> Before your patch, activation ftrace takes 550k timebase ticks. After
> your patch it takes 620k timebase ticks.
>
More details about the problem:
Before your patch, patch_instruction() is a simple, stackless function
(Note that the first branch is noped out after startup).
00000254 <patch_instruction>:
254: 48 00 00 6c b 2c0 <patch_instruction+0x6c>
258: 7c e0 00 a6 mfmsr r7
25c: 7c 51 13 a6 mtspr 81,r2
260: 3d 40 00 00 lis r10,0
262: R_PPC_ADDR16_HA .data
264: 39 4a 00 00 addi r10,r10,0
266: R_PPC_ADDR16_LO .data
268: 7c 69 1b 78 mr r9,r3
26c: 3d 29 40 00 addis r9,r9,16384
270: 81 0a 00 08 lwz r8,8(r10)
274: 55 29 00 26 rlwinm r9,r9,0,0,19
278: 81 4a 00 04 lwz r10,4(r10)
27c: 61 29 01 25 ori r9,r9,293
280: 91 28 00 00 stw r9,0(r8)
284: 55 49 00 26 rlwinm r9,r10,0,0,19
288: 50 6a 05 3e rlwimi r10,r3,0,20,31
28c: 90 8a 00 00 stw r4,0(r10)
290: 7c 00 50 6c dcbst 0,r10
294: 7c 00 04 ac hwsync
298: 7c 00 1f ac icbi 0,r3
29c: 7c 00 04 ac hwsync
2a0: 4c 00 01 2c isync
2a4: 38 60 00 00 li r3,0
2a8: 39 40 00 00 li r10,0
2ac: 91 48 00 00 stw r10,0(r8)
2b0: 7c 00 4a 64 tlbie r9,r0
2b4: 7c 00 04 ac hwsync
2b8: 7c e0 01 24 mtmsr r7
2bc: 4e 80 00 20 blr
2c0: 90 83 00 00 stw r4,0(r3)
2c4: 7c 00 18 6c dcbst 0,r3
2c8: 7c 00 04 ac hwsync
2cc: 7c 00 1f ac icbi 0,r3
2d0: 7c 00 04 ac hwsync
2d4: 4c 00 01 2c isync
2d8: 38 60 00 00 li r3,0
2dc: 4e 80 00 20 blr
2e0: 38 60 ff ff li r3,-1
2e4: 4b ff ff c4 b 2a8 <patch_instruction+0x54>
2e8: 38 60 ff ff li r3,-1
2ec: 4e 80 00 20 blr
Once your patch is there, patch_instruction() becomes a function that
has to step up a stack in order to call __do_patch_instructions().
And __do_patch_instructions() is quite a big function.
0000022c <__do_patch_instructions>:
22c: 3d 20 00 00 lis r9,0
22e: R_PPC_ADDR16_HA .data
230: 39 29 00 00 addi r9,r9,0
232: R_PPC_ADDR16_LO .data
234: 81 69 00 04 lwz r11,4(r9)
238: 2c 05 00 00 cmpwi r5,0
23c: 81 89 00 08 lwz r12,8(r9)
240: 7c c3 32 14 add r6,r3,r6
244: 55 6b 00 26 rlwinm r11,r11,0,0,19
248: 38 00 00 00 li r0,0
24c: 54 6a 05 3e clrlwi r10,r3,20
250: 21 0a 10 00 subfic r8,r10,4096
254: 7d 03 42 14 add r8,r3,r8
258: 7c 69 1b 78 mr r9,r3
25c: 7f 88 30 40 cmplw cr7,r8,r6
260: 3d 29 40 00 addis r9,r9,16384
264: 55 29 00 26 rlwinm r9,r9,0,0,19
268: 61 29 01 25 ori r9,r9,293
26c: 91 2c 00 00 stw r9,0(r12)
270: 7d 4a 5b 78 or r10,r10,r11
274: 40 9d 00 08 ble cr7,27c <__do_patch_instructions+0x50>
278: 7c c8 33 78 mr r8,r6
27c: 7f 83 40 40 cmplw cr7,r3,r8
280: 40 9c 01 2c bge cr7,3ac <__do_patch_instructions+0x180>
284: 7c 69 18 f8 not r9,r3
288: 7d 28 4a 14 add r9,r8,r9
28c: 55 29 f7 fe rlwinm r9,r9,30,31,31
290: 7c e3 50 50 subf r7,r3,r10
294: 80 a4 00 00 lwz r5,0(r4)
298: 90 aa 00 00 stw r5,0(r10)
29c: 7c 00 50 6c dcbst 0,r10
2a0: 7c 00 04 ac hwsync
2a4: 7c 00 1f ac icbi 0,r3
2a8: 7c 00 04 ac hwsync
2ac: 4c 00 01 2c isync
2b0: 38 63 00 04 addi r3,r3,4
2b4: 40 82 00 08 bne 2bc <__do_patch_instructions+0x90>
2b8: 38 84 00 04 addi r4,r4,4
2bc: 7f 83 40 40 cmplw cr7,r3,r8
2c0: 40 9c 00 a4 bge cr7,364 <__do_patch_instructions+0x138>
2c4: 2f 89 00 00 cmpwi cr7,r9,0
2c8: 41 9e 00 38 beq cr7,300 <__do_patch_instructions+0xd4>
2cc: 7d 23 3a 14 add r9,r3,r7
2d0: 81 44 00 00 lwz r10,0(r4)
2d4: 91 49 00 00 stw r10,0(r9)
2d8: 7c 00 48 6c dcbst 0,r9
2dc: 7c 00 04 ac hwsync
2e0: 7c 00 1f ac icbi 0,r3
2e4: 7c 00 04 ac hwsync
2e8: 4c 00 01 2c isync
2ec: 38 63 00 04 addi r3,r3,4
2f0: 40 82 00 08 bne 2f8 <__do_patch_instructions+0xcc>
2f4: 38 84 00 04 addi r4,r4,4
2f8: 7f 83 40 40 cmplw cr7,r3,r8
2fc: 40 9c 00 68 bge cr7,364 <__do_patch_instructions+0x138>
300: 7d 23 3a 14 add r9,r3,r7
304: 81 44 00 00 lwz r10,0(r4)
308: 91 49 00 00 stw r10,0(r9)
30c: 7c 00 48 6c dcbst 0,r9
310: 7c 00 04 ac hwsync
314: 7c 00 1f ac icbi 0,r3
318: 7c 00 04 ac hwsync
31c: 4c 00 01 2c isync
320: 38 63 00 04 addi r3,r3,4
324: 7c 69 1b 78 mr r9,r3
328: 40 82 00 08 bne 330 <__do_patch_instructions+0x104>
32c: 38 84 00 04 addi r4,r4,4
330: 7d 49 3a 14 add r10,r9,r7
334: 80 a4 00 00 lwz r5,0(r4)
338: 90 aa 00 00 stw r5,0(r10)
33c: 7c 00 50 6c dcbst 0,r10
340: 7c 00 04 ac hwsync
344: 7c 00 4f ac icbi 0,r9
348: 7c 00 04 ac hwsync
34c: 4c 00 01 2c isync
350: 38 69 00 04 addi r3,r9,4
354: 7f 83 40 40 cmplw cr7,r3,r8
358: 40 82 00 08 bne 360 <__do_patch_instructions+0x134>
35c: 38 84 00 04 addi r4,r4,4
360: 41 9c ff a0 blt cr7,300 <__do_patch_instructions+0xd4>
364: 90 0c 00 00 stw r0,0(r12)
368: 39 20 00 00 li r9,0
36c: 7c 00 5a 64 tlbie r11,r0
370: 7c 00 04 ac hwsync
374: 2f 89 00 00 cmpwi cr7,r9,0
378: 40 9e 00 2c bne cr7,3a4 <__do_patch_instructions+0x178>
37c: 7f 86 18 40 cmplw cr7,r6,r3
380: 41 9d fe cc bgt cr7,24c <__do_patch_instructions+0x20>
384: 38 60 00 00 li r3,0
388: 4e 80 00 20 blr
38c: 90 0c 00 00 stw r0,0(r12)
390: 39 20 ff ff li r9,-1
394: 7c 00 5a 64 tlbie r11,r0
398: 7c 00 04 ac hwsync
39c: 2f 89 00 00 cmpwi cr7,r9,0
3a0: 41 9e ff dc beq cr7,37c <__do_patch_instructions+0x150>
3a4: 38 60 ff ff li r3,-1
3a8: 4e 80 00 20 blr
3ac: 39 20 00 00 li r9,0
3b0: 91 2c 00 00 stw r9,0(r12)
3b4: 7c 00 5a 64 tlbie r11,r0
3b8: 7c 00 04 ac hwsync
3bc: 4b ff ff c0 b 37c <__do_patch_instructions+0x150>
000003e8 <patch_instruction>:
3e8: 94 21 ff e0 stwu r1,-32(r1)
3ec: 90 81 00 08 stw r4,8(r1)
3f0: 48 00 00 40 b 430 <patch_instruction+0x48>
3f4: 7c 08 02 a6 mflr r0
3f8: 90 01 00 24 stw r0,36(r1)
3fc: 93 e1 00 1c stw r31,28(r1)
400: 7f e0 00 a6 mfmsr r31
404: 7c 51 13 a6 mtspr 81,r2
408: 38 c0 00 04 li r6,4
40c: 38 81 00 08 addi r4,r1,8
410: 38 a0 00 00 li r5,0
414: 4b ff fe 19 bl 22c <__do_patch_instructions>
418: 7f e0 01 24 mtmsr r31
41c: 80 01 00 24 lwz r0,36(r1)
420: 83 e1 00 1c lwz r31,28(r1)
424: 7c 08 03 a6 mtlr r0
428: 38 21 00 20 addi r1,r1,32
42c: 4e 80 00 20 blr
430: 81 21 00 08 lwz r9,8(r1)
434: 91 23 00 00 stw r9,0(r3)
438: 7c 00 18 6c dcbst 0,r3
43c: 7c 00 04 ac hwsync
440: 7c 00 1f ac icbi 0,r3
444: 7c 00 04 ac hwsync
448: 4c 00 01 2c isync
44c: 38 60 00 00 li r3,0
450: 4b ff ff d8 b 428 <patch_instruction+0x40>
454: 38 60 ff ff li r3,-1
458: 4b ff ff d0 b 428 <patch_instruction+0x40>
Christophe
