* [PATCH 1/2] lib/math/test_div64: Correct the spelling of "dividend"
2021-04-22 20:36 [PATCH 0/2] MIPSr6 `do_div' support and typo fixes Maciej W. Rozycki
@ 2021-04-22 20:36 ` Maciej W. Rozycki
2021-04-22 20:36 ` [PATCH 2/2] MIPS: Avoid handcoded DIVU in `__div64_32' altogether Maciej W. Rozycki
2021-04-23 11:48 ` [PATCH 0/2] MIPSr6 `do_div' support and typo fixes Thomas Bogendoerfer
2 siblings, 0 replies; 4+ messages in thread
From: Maciej W. Rozycki @ 2021-04-22 20:36 UTC (permalink / raw)
To: Thomas Bogendoerfer
Cc: Huacai Chen, Huacai Chen, Jiaxun Yang, linux-mips, linux-kernel
The word is spelt with a final "d" of course. What a massive messup!
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
---
lib/math/test_div64.c | 38 +++++++++++++++++++-------------------
1 file changed, 19 insertions(+), 19 deletions(-)
linux-div64-test-dividend.diff
Index: linux-3maxp-div64/lib/math/test_div64.c
===================================================================
--- linux-3maxp-div64.orig/lib/math/test_div64.c
+++ linux-3maxp-div64/lib/math/test_div64.c
@@ -16,7 +16,7 @@
#define TEST_DIV64_N_ITER 1024
-static const u64 test_div64_dividents[] = {
+static const u64 test_div64_dividends[] = {
0x00000000ab275080,
0x0000000fe73c1959,
0x000000e54c0a74b1,
@@ -27,7 +27,7 @@ static const u64 test_div64_dividents[]
0x0842f488162e2284,
0xf66745411d8ab063,
};
-#define SIZE_DIV64_DIVIDENTS ARRAY_SIZE(test_div64_dividents)
+#define SIZE_DIV64_DIVIDENDS ARRAY_SIZE(test_div64_dividends)
#define TEST_DIV64_DIVISOR_0 0x00000009
#define TEST_DIV64_DIVISOR_1 0x0000007c
@@ -55,7 +55,7 @@ static const u32 test_div64_divisors[] =
static const struct {
u64 quotient;
u32 remainder;
-} test_div64_results[SIZE_DIV64_DIVISORS][SIZE_DIV64_DIVIDENTS] = {
+} test_div64_results[SIZE_DIV64_DIVISORS][SIZE_DIV64_DIVIDENDS] = {
{
{ 0x0000000013045e47, 0x00000001 },
{ 0x000000000161596c, 0x00000030 },
@@ -160,16 +160,16 @@ static inline bool test_div64_verify(u64
* to do constant propagation, and `do_div' may take a different path for
* constants, so we do want to verify that as well.
*/
-#define test_div64_one(divident, divisor, i, j) ({ \
+#define test_div64_one(dividend, divisor, i, j) ({ \
bool result = true; \
u64 quotient; \
u32 remainder; \
\
- quotient = divident; \
+ quotient = dividend; \
remainder = do_div(quotient, divisor); \
if (!test_div64_verify(quotient, remainder, i, j)) { \
pr_err("ERROR: %016llx / %08x => %016llx,%08x\n", \
- divident, divisor, quotient, remainder); \
+ dividend, divisor, quotient, remainder); \
pr_err("ERROR: expected value => %016llx,%08x\n",\
test_div64_results[i][j].quotient, \
test_div64_results[i][j].remainder); \
@@ -185,31 +185,31 @@ static inline bool test_div64_verify(u64
*/
static bool __init test_div64(void)
{
- u64 divident;
+ u64 dividend;
int i, j;
- for (i = 0; i < SIZE_DIV64_DIVIDENTS; i++) {
- divident = test_div64_dividents[i];
- if (!test_div64_one(divident, TEST_DIV64_DIVISOR_0, i, 0))
+ for (i = 0; i < SIZE_DIV64_DIVIDENDS; i++) {
+ dividend = test_div64_dividends[i];
+ if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_0, i, 0))
return false;
- if (!test_div64_one(divident, TEST_DIV64_DIVISOR_1, i, 1))
+ if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_1, i, 1))
return false;
- if (!test_div64_one(divident, TEST_DIV64_DIVISOR_2, i, 2))
+ if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_2, i, 2))
return false;
- if (!test_div64_one(divident, TEST_DIV64_DIVISOR_3, i, 3))
+ if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_3, i, 3))
return false;
- if (!test_div64_one(divident, TEST_DIV64_DIVISOR_4, i, 4))
+ if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_4, i, 4))
return false;
- if (!test_div64_one(divident, TEST_DIV64_DIVISOR_5, i, 5))
+ if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_5, i, 5))
return false;
- if (!test_div64_one(divident, TEST_DIV64_DIVISOR_6, i, 6))
+ if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_6, i, 6))
return false;
- if (!test_div64_one(divident, TEST_DIV64_DIVISOR_7, i, 7))
+ if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_7, i, 7))
return false;
- if (!test_div64_one(divident, TEST_DIV64_DIVISOR_8, i, 8))
+ if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_8, i, 8))
return false;
for (j = 0; j < SIZE_DIV64_DIVISORS; j++) {
- if (!test_div64_one(divident, test_div64_divisors[j],
+ if (!test_div64_one(dividend, test_div64_divisors[j],
i, j))
return false;
}
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH 2/2] MIPS: Avoid handcoded DIVU in `__div64_32' altogether
2021-04-22 20:36 [PATCH 0/2] MIPSr6 `do_div' support and typo fixes Maciej W. Rozycki
2021-04-22 20:36 ` [PATCH 1/2] lib/math/test_div64: Correct the spelling of "dividend" Maciej W. Rozycki
@ 2021-04-22 20:36 ` Maciej W. Rozycki
2021-04-23 11:48 ` [PATCH 0/2] MIPSr6 `do_div' support and typo fixes Thomas Bogendoerfer
2 siblings, 0 replies; 4+ messages in thread
From: Maciej W. Rozycki @ 2021-04-22 20:36 UTC (permalink / raw)
To: Thomas Bogendoerfer
Cc: Huacai Chen, Huacai Chen, Jiaxun Yang, linux-mips, linux-kernel
Remove the inline asm with a DIVU instruction from `__div64_32' and use
plain C code for the intended DIVMOD calculation instead. GCC is smart
enough to know that both the quotient and the remainder are calculated
with single DIVU, so with ISAs up to R5 the same instruction is actually
produced with overall similar code.
For R6 compiled code will work, but separate DIVU and MODU instructions
will be produced, which are also interlocked, so scalar implementations
will likely not perform as well as older ISAs with their asynchronous MD
unit. Likely still faster then the generic algorithm though.
This removes a compilation error for R6 however where the original DIVU
instruction is not supported anymore and the MDU accumulator registers
have been removed and consequently GCC complains as to a constraint it
cannot find a register for:
In file included from ./include/linux/math.h:5,
from ./include/linux/kernel.h:13,
from mm/page-writeback.c:15:
./include/linux/math64.h: In function 'div_u64_rem':
./arch/mips/include/asm/div64.h:76:17: error: inconsistent operand constraints in an 'asm'
76 | __asm__("divu $0, %z1, %z2" \
| ^~~~~~~
./include/asm-generic/div64.h:245:25: note: in expansion of macro '__div64_32'
245 | __rem = __div64_32(&(n), __base); \
| ^~~~~~~~~~
./include/linux/math64.h:91:22: note: in expansion of macro 'do_div'
91 | *remainder = do_div(dividend, divisor);
| ^~~~~~
This has passed correctness verification with test_div64 and reduced the
module's average execution time down to 1.0404s from 1.0445s with R3400
@40MHz. The module's MIPS I machine code has also shrunk by 12 bytes or
3 instructions.
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
---
arch/mips/include/asm/div64.h | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
Index: linux-3maxp-div64/arch/mips/include/asm/div64.h
===================================================================
--- linux-3maxp-div64.orig/arch/mips/include/asm/div64.h
+++ linux-3maxp-div64/arch/mips/include/asm/div64.h
@@ -58,7 +58,6 @@
#define __div64_32(n, base) ({ \
unsigned long __upper, __low, __high, __radix; \
- unsigned long long __modquot; \
unsigned long long __quot; \
unsigned long long __div; \
unsigned long __mod; \
@@ -73,11 +72,8 @@
__upper = __high; \
__high = 0; \
} else { \
- __asm__("divu $0, %z1, %z2" \
- : "=x" (__modquot) \
- : "Jr" (__high), "Jr" (__radix)); \
- __upper = __modquot >> 32; \
- __high = __modquot; \
+ __upper = __high % __radix; \
+ __high /= __radix; \
} \
\
__mod = do_div64_32(__low, __upper, __low, __radix); \
^ permalink raw reply [flat|nested] 4+ messages in thread