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Message-ID: <4092f4e9-5b2a-a5ca-946b-bb7b92a74f7c@csgroup.eu>
Date: Fri, 26 Nov 2021 17:27:56 +0000
From: LEROY Christophe <christophe.leroy@...roup.eu>
To: Michael Ellerman <mpe@...erman.id.au>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
Segher Boessenkool <segher@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH v5 1/3] powerpc/bitops: Use immediate operand when
possible
Hi Michael,
Any chance to get this series merged this cycle ?
Thanks
Christophe
Le 21/09/2021 à 17:09, Christophe Leroy a écrit :
> Today we get the following code generation for bitops like
> set or clear bit:
>
> c0009fe0: 39 40 08 00 li r10,2048
> c0009fe4: 7c e0 40 28 lwarx r7,0,r8
> c0009fe8: 7c e7 53 78 or r7,r7,r10
> c0009fec: 7c e0 41 2d stwcx. r7,0,r8
>
> c000d568: 39 00 18 00 li r8,6144
> c000d56c: 7c c0 38 28 lwarx r6,0,r7
> c000d570: 7c c6 40 78 andc r6,r6,r8
> c000d574: 7c c0 39 2d stwcx. r6,0,r7
>
> Most set bits are constant on lower 16 bits, so it can easily
> be replaced by the "immediate" version of the operation. Allow
> GCC to choose between the normal or immediate form.
>
> For clear bits, on 32 bits 'rlwinm' can be used instead of 'andc' for
> when all bits to be cleared are consecutive.
>
> On 64 bits we don't have any equivalent single operation for clearing,
> single bits or a few bits, we'd need two 'rldicl' so it is not
> worth it, the li/andc sequence is doing the same.
>
> With this patch we get:
>
> c0009fe0: 7d 00 50 28 lwarx r8,0,r10
> c0009fe4: 61 08 08 00 ori r8,r8,2048
> c0009fe8: 7d 00 51 2d stwcx. r8,0,r10
>
> c000d558: 7c e0 40 28 lwarx r7,0,r8
> c000d55c: 54 e7 05 64 rlwinm r7,r7,0,21,18
> c000d560: 7c e0 41 2d stwcx. r7,0,r8
>
> On pmac32_defconfig, it reduces the text by approx 10 kbytes.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> Reviewed-by: Segher Boessenkool <segher@...nel.crashing.org>
> ---
> v5: Fixed the argument of is_rlwinm_mask_valid() in test_and_clear_bits()
>
> v4: Rebased
>
> v3:
> - Using the mask validation proposed by Segher
>
> v2:
> - Use "n" instead of "i" as constraint for the rlwinm mask
> - Improve mask verification to handle more than single bit masks
>
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
> arch/powerpc/include/asm/bitops.h | 89 ++++++++++++++++++++++++++++---
> 1 file changed, 81 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/bitops.h b/arch/powerpc/include/asm/bitops.h
> index 11847b6a244e..a05d8c62cbea 100644
> --- a/arch/powerpc/include/asm/bitops.h
> +++ b/arch/powerpc/include/asm/bitops.h
> @@ -71,19 +71,61 @@ static inline void fn(unsigned long mask, \
> __asm__ __volatile__ ( \
> prefix \
> "1:" PPC_LLARX "%0,0,%3,0\n" \
> - stringify_in_c(op) "%0,%0,%2\n" \
> + #op "%I2 %0,%0,%2\n" \
> PPC_STLCX "%0,0,%3\n" \
> "bne- 1b\n" \
> : "=&r" (old), "+m" (*p) \
> - : "r" (mask), "r" (p) \
> + : "rK" (mask), "r" (p) \
> : "cc", "memory"); \
> }
>
> DEFINE_BITOP(set_bits, or, "")
> -DEFINE_BITOP(clear_bits, andc, "")
> -DEFINE_BITOP(clear_bits_unlock, andc, PPC_RELEASE_BARRIER)
> DEFINE_BITOP(change_bits, xor, "")
>
> +static __always_inline bool is_rlwinm_mask_valid(unsigned long x)
> +{
> + if (!x)
> + return false;
> + if (x & 1)
> + x = ~x; // make the mask non-wrapping
> + x += x & -x; // adding the low set bit results in at most one bit set
> +
> + return !(x & (x - 1));
> +}
> +
> +#define DEFINE_CLROP(fn, prefix) \
> +static inline void fn(unsigned long mask, volatile unsigned long *_p) \
> +{ \
> + unsigned long old; \
> + unsigned long *p = (unsigned long *)_p; \
> + \
> + if (IS_ENABLED(CONFIG_PPC32) && \
> + __builtin_constant_p(mask) && is_rlwinm_mask_valid(~mask)) {\
> + asm volatile ( \
> + prefix \
> + "1:" "lwarx %0,0,%3\n" \
> + "rlwinm %0,%0,0,%2\n" \
> + "stwcx. %0,0,%3\n" \
> + "bne- 1b\n" \
> + : "=&r" (old), "+m" (*p) \
> + : "n" (~mask), "r" (p) \
> + : "cc", "memory"); \
> + } else { \
> + asm volatile ( \
> + prefix \
> + "1:" PPC_LLARX "%0,0,%3,0\n" \
> + "andc %0,%0,%2\n" \
> + PPC_STLCX "%0,0,%3\n" \
> + "bne- 1b\n" \
> + : "=&r" (old), "+m" (*p) \
> + : "r" (mask), "r" (p) \
> + : "cc", "memory"); \
> + } \
> +}
> +
> +DEFINE_CLROP(clear_bits, "")
> +DEFINE_CLROP(clear_bits_unlock, PPC_RELEASE_BARRIER)
> +
> static inline void arch_set_bit(int nr, volatile unsigned long *addr)
> {
> set_bits(BIT_MASK(nr), addr + BIT_WORD(nr));
> @@ -116,12 +158,12 @@ static inline unsigned long fn( \
> __asm__ __volatile__ ( \
> prefix \
> "1:" PPC_LLARX "%0,0,%3,%4\n" \
> - stringify_in_c(op) "%1,%0,%2\n" \
> + #op "%I2 %1,%0,%2\n" \
> PPC_STLCX "%1,0,%3\n" \
> "bne- 1b\n" \
> postfix \
> : "=&r" (old), "=&r" (t) \
> - : "r" (mask), "r" (p), "i" (IS_ENABLED(CONFIG_PPC64) ? eh : 0) \
> + : "rK" (mask), "r" (p), "i" (IS_ENABLED(CONFIG_PPC64) ? eh : 0) \
> : "cc", "memory"); \
> return (old & mask); \
> }
> @@ -130,11 +172,42 @@ DEFINE_TESTOP(test_and_set_bits, or, PPC_ATOMIC_ENTRY_BARRIER,
> PPC_ATOMIC_EXIT_BARRIER, 0)
> DEFINE_TESTOP(test_and_set_bits_lock, or, "",
> PPC_ACQUIRE_BARRIER, 1)
> -DEFINE_TESTOP(test_and_clear_bits, andc, PPC_ATOMIC_ENTRY_BARRIER,
> - PPC_ATOMIC_EXIT_BARRIER, 0)
> DEFINE_TESTOP(test_and_change_bits, xor, PPC_ATOMIC_ENTRY_BARRIER,
> PPC_ATOMIC_EXIT_BARRIER, 0)
>
> +static inline unsigned long test_and_clear_bits(unsigned long mask, volatile unsigned long *_p)
> +{
> + unsigned long old, t;
> + unsigned long *p = (unsigned long *)_p;
> +
> + if (IS_ENABLED(CONFIG_PPC32) &&
> + __builtin_constant_p(mask) && is_rlwinm_mask_valid(~mask)) {
> + asm volatile (
> + PPC_ATOMIC_ENTRY_BARRIER
> + "1:" "lwarx %0,0,%3\n"
> + "rlwinm %1,%0,0,%2\n"
> + "stwcx. %1,0,%3\n"
> + "bne- 1b\n"
> + PPC_ATOMIC_EXIT_BARRIER
> + : "=&r" (old), "=&r" (t)
> + : "n" (~mask), "r" (p)
> + : "cc", "memory");
> + } else {
> + asm volatile (
> + PPC_ATOMIC_ENTRY_BARRIER
> + "1:" PPC_LLARX "%0,0,%3,0\n"
> + "andc %1,%0,%2\n"
> + PPC_STLCX "%1,0,%3\n"
> + "bne- 1b\n"
> + PPC_ATOMIC_EXIT_BARRIER
> + : "=&r" (old), "=&r" (t)
> + : "r" (mask), "r" (p)
> + : "cc", "memory");
> + }
> +
> + return (old & mask);
> +}
> +
> static inline int arch_test_and_set_bit(unsigned long nr,
> volatile unsigned long *addr)
> {
>
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