Re: [PATCH] compiler_types: Introduce inline_for

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* Re: [PATCH] compiler_types: Introduce inline_for_performance
       [not found] <20260118152448.2560414-1-edumazet@google.com>
@ 2026-01-18 18:36 ` kernel test robot
  2026-01-18 22:33   ` David Laight
  2026-01-18 21:04 ` kernel test robot
  1 sibling, 1 reply; 3+ messages in thread
From: kernel test robot @ 2026-01-18 18:36 UTC (permalink / raw)
  To: Eric Dumazet, Andrew Morton
  Cc: oe-kbuild-all, Linux Memory Management List, linux-kernel,
	netdev, Jakub Kicinski, Eric Dumazet, Paolo Abeni, Nicolas Pitre

Hi Eric,

kernel test robot noticed the following build warnings:

[auto build test WARNING on e84d960149e71e8d5e4db69775ce31305898ed0c]

url:    https://github.com/intel-lab-lkp/linux/commits/Eric-Dumazet/compiler_types-Introduce-inline_for_performance/20260118-232653
base:   e84d960149e71e8d5e4db69775ce31305898ed0c
patch link:    https://lore.kernel.org/r/20260118152448.2560414-1-edumazet%40google.com
patch subject: [PATCH] compiler_types: Introduce inline_for_performance
config: m68k-amcore_defconfig (https://download.01.org/0day-ci/archive/20260119/202601190247.dDAvbbMH-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 15.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260119/202601190247.dDAvbbMH-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202601190247.dDAvbbMH-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from arch/m68k/include/asm/div64.h:6,
                    from include/linux/math.h:6,
                    from include/linux/kernel.h:27,
                    from arch/m68k/coldfire/cache.c:12:
>> include/asm-generic/div64.h:138:10: warning: '__arch_xprod_64' defined but not used [-Wunused-function]
     138 | uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
         |          ^~~~~~~~~~~~~~~


vim +/__arch_xprod_64 +138 include/asm-generic/div64.h

461a5e51060c93 Nicolas Pitre 2015-10-30  125  
f682b27c57aec2 Nicolas Pitre 2015-10-30  126  #ifndef __arch_xprod_64
f682b27c57aec2 Nicolas Pitre 2015-10-30  127  /*
f682b27c57aec2 Nicolas Pitre 2015-10-30  128   * Default C implementation for __arch_xprod_64()
f682b27c57aec2 Nicolas Pitre 2015-10-30  129   *
f682b27c57aec2 Nicolas Pitre 2015-10-30  130   * Prototype: uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
f682b27c57aec2 Nicolas Pitre 2015-10-30  131   * Semantic:  retval = ((bias ? m : 0) + m * n) >> 64
f682b27c57aec2 Nicolas Pitre 2015-10-30  132   *
f682b27c57aec2 Nicolas Pitre 2015-10-30  133   * The product is a 128-bit value, scaled down to 64 bits.
00a31dd3acea0f Nicolas Pitre 2024-10-03  134   * Hoping for compile-time optimization of  conditional code.
f682b27c57aec2 Nicolas Pitre 2015-10-30  135   * Architectures may provide their own optimized assembly implementation.
f682b27c57aec2 Nicolas Pitre 2015-10-30  136   */
5f712d70e20a46 Eric Dumazet  2026-01-18  137  static inline_for_performance
d533cb2d2af400 Nicolas Pitre 2024-10-03 @138  uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
f682b27c57aec2 Nicolas Pitre 2015-10-30  139  {
f682b27c57aec2 Nicolas Pitre 2015-10-30  140  	uint32_t m_lo = m;
f682b27c57aec2 Nicolas Pitre 2015-10-30  141  	uint32_t m_hi = m >> 32;
f682b27c57aec2 Nicolas Pitre 2015-10-30  142  	uint32_t n_lo = n;
f682b27c57aec2 Nicolas Pitre 2015-10-30  143  	uint32_t n_hi = n >> 32;
00a31dd3acea0f Nicolas Pitre 2024-10-03  144  	uint64_t x, y;
f682b27c57aec2 Nicolas Pitre 2015-10-30  145  
00a31dd3acea0f Nicolas Pitre 2024-10-03  146  	/* Determine if overflow handling can be dispensed with. */
00a31dd3acea0f Nicolas Pitre 2024-10-03  147  	bool no_ovf = __builtin_constant_p(m) &&
00a31dd3acea0f Nicolas Pitre 2024-10-03  148  		      ((m >> 32) + (m & 0xffffffff) < 0x100000000);
f682b27c57aec2 Nicolas Pitre 2015-10-30  149  
00a31dd3acea0f Nicolas Pitre 2024-10-03  150  	if (no_ovf) {
00a31dd3acea0f Nicolas Pitre 2024-10-03  151  		x = (uint64_t)m_lo * n_lo + (bias ? m : 0);
00a31dd3acea0f Nicolas Pitre 2024-10-03  152  		x >>= 32;
00a31dd3acea0f Nicolas Pitre 2024-10-03  153  		x += (uint64_t)m_lo * n_hi;
00a31dd3acea0f Nicolas Pitre 2024-10-03  154  		x += (uint64_t)m_hi * n_lo;
00a31dd3acea0f Nicolas Pitre 2024-10-03  155  		x >>= 32;
00a31dd3acea0f Nicolas Pitre 2024-10-03  156  		x += (uint64_t)m_hi * n_hi;
f682b27c57aec2 Nicolas Pitre 2015-10-30  157  	} else {
00a31dd3acea0f Nicolas Pitre 2024-10-03  158  		x = (uint64_t)m_lo * n_lo + (bias ? m_lo : 0);
00a31dd3acea0f Nicolas Pitre 2024-10-03  159  		y = (uint64_t)m_lo * n_hi + (uint32_t)(x >> 32) + (bias ? m_hi : 0);
00a31dd3acea0f Nicolas Pitre 2024-10-03  160  		x = (uint64_t)m_hi * n_hi + (uint32_t)(y >> 32);
00a31dd3acea0f Nicolas Pitre 2024-10-03  161  		y = (uint64_t)m_hi * n_lo + (uint32_t)y;
00a31dd3acea0f Nicolas Pitre 2024-10-03  162  		x += (uint32_t)(y >> 32);
f682b27c57aec2 Nicolas Pitre 2015-10-30  163  	}
f682b27c57aec2 Nicolas Pitre 2015-10-30  164  
00a31dd3acea0f Nicolas Pitre 2024-10-03  165  	return x;
f682b27c57aec2 Nicolas Pitre 2015-10-30  166  }
f682b27c57aec2 Nicolas Pitre 2015-10-30  167  #endif
f682b27c57aec2 Nicolas Pitre 2015-10-30  168  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki


^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] compiler_types: Introduce inline_for_performance
  2026-01-18 18:36 ` [PATCH] compiler_types: Introduce inline_for_performance kernel test robot
@ 2026-01-18 22:33   ` David Laight
  0 siblings, 0 replies; 3+ messages in thread
From: David Laight @ 2026-01-18 22:33 UTC (permalink / raw)
  To: kernel test robot
  Cc: Eric Dumazet, Andrew Morton, oe-kbuild-all,
	Linux Memory Management List, linux-kernel, netdev,
	Jakub Kicinski, Eric Dumazet, Paolo Abeni, Nicolas Pitre

On Mon, 19 Jan 2026 02:36:18 +0800
kernel test robot <lkp@intel.com> wrote:

> Hi Eric,
...
> vim +/__arch_xprod_64 +138 include/asm-generic/div64.h
> 
> 461a5e51060c93 Nicolas Pitre 2015-10-30  125  
> f682b27c57aec2 Nicolas Pitre 2015-10-30  126  #ifndef __arch_xprod_64
> f682b27c57aec2 Nicolas Pitre 2015-10-30  127  /*
> f682b27c57aec2 Nicolas Pitre 2015-10-30  128   * Default C implementation for __arch_xprod_64()
> f682b27c57aec2 Nicolas Pitre 2015-10-30  129   *
> f682b27c57aec2 Nicolas Pitre 2015-10-30  130   * Prototype: uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
> f682b27c57aec2 Nicolas Pitre 2015-10-30  131   * Semantic:  retval = ((bias ? m : 0) + m * n) >> 64
> f682b27c57aec2 Nicolas Pitre 2015-10-30  132   *
> f682b27c57aec2 Nicolas Pitre 2015-10-30  133   * The product is a 128-bit value, scaled down to 64 bits.
> 00a31dd3acea0f Nicolas Pitre 2024-10-03  134   * Hoping for compile-time optimization of  conditional code.
> f682b27c57aec2 Nicolas Pitre 2015-10-30  135   * Architectures may provide their own optimized assembly implementation.
> f682b27c57aec2 Nicolas Pitre 2015-10-30  136   */
> 5f712d70e20a46 Eric Dumazet  2026-01-18  137  static inline_for_performance
> d533cb2d2af400 Nicolas Pitre 2024-10-03 @138  uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
> f682b27c57aec2 Nicolas Pitre 2015-10-30  139  {
> f682b27c57aec2 Nicolas Pitre 2015-10-30  140  	uint32_t m_lo = m;
> f682b27c57aec2 Nicolas Pitre 2015-10-30  141  	uint32_t m_hi = m >> 32;
> f682b27c57aec2 Nicolas Pitre 2015-10-30  142  	uint32_t n_lo = n;
> f682b27c57aec2 Nicolas Pitre 2015-10-30  143  	uint32_t n_hi = n >> 32;
> 00a31dd3acea0f Nicolas Pitre 2024-10-03  144  	uint64_t x, y;
> f682b27c57aec2 Nicolas Pitre 2015-10-30  145  
> 00a31dd3acea0f Nicolas Pitre 2024-10-03  146  	/* Determine if overflow handling can be dispensed with. */
> 00a31dd3acea0f Nicolas Pitre 2024-10-03  147  	bool no_ovf = __builtin_constant_p(m) &&
> 00a31dd3acea0f Nicolas Pitre 2024-10-03  148  		      ((m >> 32) + (m & 0xffffffff) < 0x100000000);

Can that ever have got compiled?
Won't the compiler complain about 0x100000000 being out of range?
Lots of alternatives...

If u128 exists this should probably just be:
	return ((u128)m * n + (bias ? m : 0)) >> 64;

Which is probably the only alternative an architecture might provide (none do AFAICT).

	David


^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] compiler_types: Introduce inline_for_performance
       [not found] <20260118152448.2560414-1-edumazet@google.com>
  2026-01-18 18:36 ` [PATCH] compiler_types: Introduce inline_for_performance kernel test robot
@ 2026-01-18 21:04 ` kernel test robot
  1 sibling, 0 replies; 3+ messages in thread
From: kernel test robot @ 2026-01-18 21:04 UTC (permalink / raw)
  To: Eric Dumazet, Andrew Morton
  Cc: oe-kbuild-all, Linux Memory Management List, linux-kernel,
	netdev, Jakub Kicinski, Eric Dumazet, Paolo Abeni, Nicolas Pitre

Hi Eric,

kernel test robot noticed the following build warnings:

[auto build test WARNING on e84d960149e71e8d5e4db69775ce31305898ed0c]

url:    https://github.com/intel-lab-lkp/linux/commits/Eric-Dumazet/compiler_types-Introduce-inline_for_performance/20260118-232653
base:   e84d960149e71e8d5e4db69775ce31305898ed0c
patch link:    https://lore.kernel.org/r/20260118152448.2560414-1-edumazet%40google.com
patch subject: [PATCH] compiler_types: Introduce inline_for_performance
config: arm-randconfig-004-20260119 (https://download.01.org/0day-ci/archive/20260119/202601190420.RlBoZSGm-lkp@intel.com/config)
compiler: arm-linux-gnueabi-gcc (GCC) 14.3.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260119/202601190420.RlBoZSGm-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202601190420.RlBoZSGm-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from include/linux/math.h:6,
                    from include/linux/kernel.h:27,
                    from include/linux/random.h:7,
                    from include/linux/nodemask.h:94,
                    from include/linux/numa.h:6,
                    from include/linux/cpumask.h:15,
                    from include/linux/smp.h:13,
                    from include/linux/lockdep.h:14,
                    from include/linux/spinlock.h:63,
                    from lib/dec_and_lock.c:3:
>> arch/arm/include/asm/div64.h:56:10: warning: '__arch_xprod_64' defined but not used [-Wunused-function]
      56 | uint64_t __arch_xprod_64(uint64_t m, uint64_t n, bool bias)
         |          ^~~~~~~~~~~~~~~


vim +/__arch_xprod_64 +56 arch/arm/include/asm/div64.h

fa4adc614922c2 include/asm-arm/div64.h      Nicolas Pitre 2006-12-06   54  
5f712d70e20a46 arch/arm/include/asm/div64.h Eric Dumazet  2026-01-18   55  static inline_for_performance
d533cb2d2af400 arch/arm/include/asm/div64.h Nicolas Pitre 2024-10-03  @56  uint64_t __arch_xprod_64(uint64_t m, uint64_t n, bool bias)
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   57  {
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   58  	unsigned long long res;
73e592f3bc2cdc arch/arm/include/asm/div64.h Nicolas Pitre 2016-01-27   59  	register unsigned int tmp asm("ip") = 0;
06508533d51a1d arch/arm/include/asm/div64.h Nicolas Pitre 2024-10-03   60  	bool no_ovf = __builtin_constant_p(m) &&
06508533d51a1d arch/arm/include/asm/div64.h Nicolas Pitre 2024-10-03   61  		      ((m >> 32) + (m & 0xffffffff) < 0x100000000);
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   62  
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   63  	if (!bias) {
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   64  		asm (	"umull	%Q0, %R0, %Q1, %Q2\n\t"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   65  			"mov	%Q0, #0"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   66  			: "=&r" (res)
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   67  			: "r" (m), "r" (n)
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   68  			: "cc");
06508533d51a1d arch/arm/include/asm/div64.h Nicolas Pitre 2024-10-03   69  	} else if (no_ovf) {
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   70  		res = m;
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   71  		asm (	"umlal	%Q0, %R0, %Q1, %Q2\n\t"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   72  			"mov	%Q0, #0"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   73  			: "+&r" (res)
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   74  			: "r" (m), "r" (n)
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   75  			: "cc");
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   76  	} else {
73e592f3bc2cdc arch/arm/include/asm/div64.h Nicolas Pitre 2016-01-27   77  		asm (	"umull	%Q0, %R0, %Q2, %Q3\n\t"
73e592f3bc2cdc arch/arm/include/asm/div64.h Nicolas Pitre 2016-01-27   78  			"cmn	%Q0, %Q2\n\t"
73e592f3bc2cdc arch/arm/include/asm/div64.h Nicolas Pitre 2016-01-27   79  			"adcs	%R0, %R0, %R2\n\t"
73e592f3bc2cdc arch/arm/include/asm/div64.h Nicolas Pitre 2016-01-27   80  			"adc	%Q0, %1, #0"
73e592f3bc2cdc arch/arm/include/asm/div64.h Nicolas Pitre 2016-01-27   81  			: "=&r" (res), "+&r" (tmp)
73e592f3bc2cdc arch/arm/include/asm/div64.h Nicolas Pitre 2016-01-27   82  			: "r" (m), "r" (n)
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   83  			: "cc");
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   84  	}
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   85  
06508533d51a1d arch/arm/include/asm/div64.h Nicolas Pitre 2024-10-03   86  	if (no_ovf) {
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   87  		asm (	"umlal	%R0, %Q0, %R1, %Q2\n\t"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   88  			"umlal	%R0, %Q0, %Q1, %R2\n\t"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   89  			"mov	%R0, #0\n\t"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   90  			"umlal	%Q0, %R0, %R1, %R2"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   91  			: "+&r" (res)
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   92  			: "r" (m), "r" (n)
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   93  			: "cc");
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   94  	} else {
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   95  		asm (	"umlal	%R0, %Q0, %R2, %Q3\n\t"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   96  			"umlal	%R0, %1, %Q2, %R3\n\t"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   97  			"mov	%R0, #0\n\t"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   98  			"adds	%Q0, %1, %Q0\n\t"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02   99  			"adc	%R0, %R0, #0\n\t"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02  100  			"umlal	%Q0, %R0, %R2, %R3"
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02  101  			: "+&r" (res), "+&r" (tmp)
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02  102  			: "r" (m), "r" (n)
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02  103  			: "cc");
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02  104  	}
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02  105  
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02  106  	return res;
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02  107  }
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02  108  #define __arch_xprod_64 __arch_xprod_64
040b323b5012b5 arch/arm/include/asm/div64.h Nicolas Pitre 2015-11-02  109  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki


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2026-01-18 18:36 ` [PATCH] compiler_types: Introduce inline_for_performance kernel test robot
2026-01-18 22:33   ` David Laight
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