GCC rychle kopirovani pameti
Jaroslav Buchta
jaroslav.buchta na hascomp.cz
Sobota Červen 9 11:42:59 CEST 2018
To by asi slo ale zas tak kriticke to casove neni, par us uz je OK.
Jeste si sypu popel na hlavu s tou aritmetikou na void*, uz jsem to
opravil i kdyz GCC to dava spravne (tusim, ze to ma definovano jakop
nejake rozsireni)
Dne 09.06.2018 v 11:38 Stano napsal(a):
> Neskusali ste tu cast kopirujucu po 64..32bit nahradit DMA prenosom?
> 100B je pomerne malo alemyslim ze uz byto nieco malo usetrit mohlo.
>
> On 9. 6. 2018 11:20, Jaroslav Buchta wrote:
>> To je mi jasne, ze ten kod neni univerzalni ale je to urceno
>> specialne pro kopirovani jedne struktury dlouhe cca 100B v casove
>> kriticke ISR , ktera je zarovnana na 4B a tim padem OK. Predpokladam
>> tedy, ze instrukcim ldrd a strd neni potreba zarovnat adresu modulo 8
>> ? Ten druhy while ma byt samozrejme take if, ale prelozi se to
>> stejne. memcpy trvalo tusim pres 10us a tato funkce to zvladne pod
>> 3us (STM32F3)
>>
>> Dne 09.06.2018 v 8:07 Ondrej napsal(a):
>>> Ještě jeden dodatek: co když bude adresa SRC 1 a adresa DST 3 a LEN
>>> 15. Bude váš kód fungovat nebo vyhodí výjimku Unaligned memory
>>> access nebo zkopíruje něco někam kam nemá?
>>>
>>>
>>> Ondřej
>>>
>>>
>>> Dne 9.6.2018 v 7:33 Ondrej napsal(a):
>>>> Nevím jak GCC ale Visual Studio a Borland měli na memcopy také dost
>>>> odlišný názor. Řešení VS bylo asi 3x rychlejší, ale ten ASM kód byl
>>>> nepochopitelný - jako kdyby inicializoval nějaké DMA. A to stále
>>>> bavíme o kódu pro Windows.
>>>>
>>>> Ondřej
>>>>
>>>> Dne 8.6.2018 v 12:09 Jaroslav Buchta napsal(a):
>>>>> Resenim je dat fci fastcopy do jineho modulu ale stejne by me
>>>>> zajimalo, jestli to je normalni.
>>>>>
>>>>> Dne 08.06.2018 v 12:01 Jaroslav Buchta napsal(a):
>>>>>> Zdravim, dnes se zase nestiham divit, nevim, na cem je to jak
>>>>>> zavisle ale bezna funkce memcpy vede jak v optimalizovanem tak v
>>>>>> neoptimalizovanem prekladu k hloupemu kopirovani po 1B
>>>>>>
>>>>>> Zkusil jsem si napsat takovouto fci
>>>>>>
>>>>>> void fastcpy(void *dst, void *src, int len)
>>>>>> {
>>>>>> while (len >= 8)
>>>>>> {
>>>>>> *(uint64_t*)dst = *(uint64_t*)src;
>>>>>> dst += 8;
>>>>>> src += 8;
>>>>>> len -= 8;
>>>>>> }
>>>>>> while (len >= 4)
>>>>>> {
>>>>>> *(uint32_t*)dst = *(uint32_t*)src;
>>>>>> dst += 4;
>>>>>> src += 4;
>>>>>> len -= 4;
>>>>>> }
>>>>>> if (len >= 2)
>>>>>> {
>>>>>> *(uint16_t*)dst = *(uint16_t*)src;
>>>>>> dst += 2;
>>>>>> src += 2;
>>>>>> len -= 2;
>>>>>> }
>>>>>> if (len != 0)
>>>>>> {
>>>>>> *(uint8_t*)dst = *(uint8_t*)src;
>>>>>> }
>>>>>> }
>>>>>>
>>>>>> ktera vede ke kyzenemu vysledku, je to vyrazne rychlejsi, ovsem
>>>>>> POUZE, KDYZ NENI NASTAVENA OPTIMALIZACE O3, tam nejak prekladac
>>>>>> usoudi, ze je to kopirovani bloku a vola memcpy... Je to vubec
>>>>>> mozne, nebo delam nejakou chybu???
>>>>>>
>>>>>> Jak mam vynutit volani te funkce? (krome obchuzky, ze pro ni
>>>>>> zakazu optimalizaci...)
>>>>>>
>>>>>>
>>>>>> ////////////////////////////////
>>>>>>
>>>>>> Optimalizovany kod:
>>>>>>
>>>>>> 100 mccState.iB = (float)(mccState.bufAdc1[2]);
>>>>>> 080004c2: vstr s14, [r4, #68] ; 0x44
>>>>>> 080004c6: vstr s15, [r4, #72] ; 0x48
>>>>>> 102 if (!mccStateCopy.f_LockCopy)
>>>>>> 080004ca: bmi.n 0x8000400 <HAL_ADC_ConvCpltCallback+24>
>>>>>> 080004cc: movs r2, #72 ; 0x48
>>>>>> 080004ce: mov r1, r4
>>>>>> 080004d0: add.w r0, r4, #76 ; 0x4c
>>>>>> 080004d4: bl 0x8005e00 <memcpy>
>>>>>> 72 *(uint32_t*)dst = *(uint32_t*)src;
>>>>>>
>>>>>>
>>>>>> Neoptimalizovany kod:
>>>>>>
>>>>>> 101 mccState.iC = (float)(mccState.bufAdc1[3]);
>>>>>> 08000528: vmov s15, r1
>>>>>> 0800052c: vcvt.f32.u32 s15, s15
>>>>>> 08000530: vstr s15, [r3, #72] ; 0x48
>>>>>> 102 if (!mccStateCopy.f_LockCopy)
>>>>>> 08000534: ldrb.w r3, [r3, #76] ; 0x4c
>>>>>> 08000538: tst.w r3, #2
>>>>>> 0800053c: bne.n 0x8000470 <HAL_ADC_ConvCpltCallback+24>
>>>>>> 104 fastcpy((void *)&mccStateCopy, (void
>>>>>> *)&mccState, sizeof(MCCOMSTATE));
>>>>>> 0800053e: ldr r0, [pc, #16] ; (0x8000550
>>>>>> <HAL_ADC_ConvCpltCallback+248>)
>>>>>> 08000540: movs r2, #76 ; 0x4c
>>>>>> 08000542: mov r1, r0
>>>>>> 08000544: add r0, r2
>>>>>> 08000546: bl 0x80003f4 <fastcpy>
>>>>>>
>>>>>>
>>>>>> fastcpy:
>>>>>> 080003f4: cmp r2, #7
>>>>>> 080003f6: ble.n 0x800043a <fastcpy+70>
>>>>>> 62 {
>>>>>> 080003f8: push {r4, r5}
>>>>>> 65 *(uint64_t*)dst = *(uint64_t*)src;
>>>>>> 080003fa: ldrd r4, r5, [r1], #8
>>>>>> 080003fe: strd r4, r5, [r0], #8
>>>>>> 68 len -= 8;
>>>>>> 08000402: subs r2, #8
>>>>>> 63 while (len >= 8)
>>>>>> 08000404: cmp r2, #7
>>>>>> 08000406: bgt.n 0x80003fa <fastcpy+6>
>>>>>> 08000408: b.n 0x8000414 <fastcpy+32>
>>>>>> 72 *(uint32_t*)dst = *(uint32_t*)src;
>>>>>> 0800040a: ldr.w r3, [r1], #4
>>>>>> 0800040e: str.w r3, [r0], #4
>>>>>> 75 len -= 4;
>>>>>> 08000412: subs r2, #4
>>>>>> 70 while (len >= 4)
>>>>>> 08000414: cmp r2, #3
>>>>>> 08000416: bgt.n 0x800040a <fastcpy+22>
>>>>>> 77 if (len >= 2)
>>>>>> 08000418: cmp r2, #1
>>>>>> 0800041a: ble.n 0x8000426 <fastcpy+50>
>>>>>> 79 *(uint16_t*)dst = *(uint16_t*)src;
>>>>>> 0800041c: ldrh.w r3, [r1], #2
>>>>>> 08000420: strh.w r3, [r0], #2
>>>>>> 82 len -= 2;
>>>>>> 08000424: subs r2, #2
>>>>>> 84 if (len != 0)
>>>>>> 08000426: cbz r2, 0x800042c <fastcpy+56>
>>>>>> 86 *(uint8_t*)dst = *(uint8_t*)src;
>>>>>> 08000428: ldrb r3, [r1, #0]
>>>>>> 0800042a: strb r3, [r0, #0]
>>>>>> 88 }
>>>>>> 0800042c: pop {r4, r5}
>>>>>> 0800042e: bx lr
>>>>>> 08000430: ldr.w r3, [r1], #4
>>>>>> 08000434: str.w r3, [r0], #4
>>>>>> 75 len -= 4;
>>>>>> 08000438: subs r2, #4
>>>>>> 0800043a: cmp r2, #3
>>>>>> 0800043c: bgt.n 0x8000430 <fastcpy+60>
>>>>>> 0800043e: cmp r2, #1
>>>>>> 08000440: ble.n 0x800044c <fastcpy+88>
>>>>>> 08000442: ldrh.w r3, [r1], #2
>>>>>> 08000446: strh.w r3, [r0], #2
>>>>>> 82 len -= 2;
>>>>>> 0800044a: subs r2, #2
>>>>>> 84 if (len != 0)
>>>>>> 0800044c: cmp r2, #0
>>>>>> 0800044e: beq.n 0x800042e <fastcpy+58>
>>>>>> 86 *(uint8_t*)dst = *(uint8_t*)src;
>>>>>> 08000450: ldrb r3, [r1, #0]
>>>>>> 08000452: strb r3, [r0, #0]
>>>>>> 08000454: bx lr
>>>>>>
>>>>>>
>>>>>>
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