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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Sep 2025 16:19:48.4784 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: dca9a745-077b-46f7-c51f-08ddf14f076d X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DU6PEPF0000A7DD.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PAXPR08MB7550 Hi Will, [...] > > arch/arm64/include/asm/futex.h | 43 ++++++++++++++++++++++++++++------ > > 1 file changed, 36 insertions(+), 7 deletions(-) > > > > diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h > > index ab7003cb4724..22a6301a9f3d 100644 > > --- a/arch/arm64/include/asm/futex.h > > +++ b/arch/arm64/include/asm/futex.h > > @@ -13,7 +13,7 @@ > > > > #define LLSC_MAX_LOOPS 128 /* What's the largest number you can think of? */ > > > > -#define LLSC_FUTEX_ATOMIC_OP(op, insn) \ > > +#define LLSC_FUTEX_ATOMIC_OP(op, asm_op) \ > > static __always_inline int \ > > __llsc_futex_atomic_##op(int oparg, u32 __user *uaddr, int *oval) \ > > { \ > > @@ -24,7 +24,7 @@ __llsc_futex_atomic_##op(int oparg, u32 __user *uaddr, int *oval) \ > > asm volatile("// __llsc_futex_atomic_" #op "\n" \ > > " prfm pstl1strm, %2\n" \ > > "1: ldxr %w1, %2\n" \ > > - insn "\n" \ > > +" " #asm_op " %w3, %w1, %w5\n" \ > > "2: stlxr %w0, %w3, %2\n" \ > > " cbz %w0, 3f\n" \ > > " sub %w4, %w4, %w0\n" \ > > @@ -46,11 +46,40 @@ __llsc_futex_atomic_##op(int oparg, u32 __user *uaddr, int *oval) \ > > return ret; \ > > } > > > > -LLSC_FUTEX_ATOMIC_OP(add, "add %w3, %w1, %w5") > > -LLSC_FUTEX_ATOMIC_OP(or, "orr %w3, %w1, %w5") > > -LLSC_FUTEX_ATOMIC_OP(and, "and %w3, %w1, %w5") > > -LLSC_FUTEX_ATOMIC_OP(eor, "eor %w3, %w1, %w5") > > -LLSC_FUTEX_ATOMIC_OP(set, "mov %w3, %w5") > > +LLSC_FUTEX_ATOMIC_OP(add, add) > > +LLSC_FUTEX_ATOMIC_OP(or, orr) > > +LLSC_FUTEX_ATOMIC_OP(and, and) > > +LLSC_FUTEX_ATOMIC_OP(eor, eor) > > + > > +static __always_inline int > > +__llsc_futex_atomic_set(int oparg, u32 __user *uaddr, int *oval) > > +{ > > + unsigned int loops = LLSC_MAX_LOOPS; > > + int ret, oldval; > > + > > + uaccess_enable_privileged(); > > + asm volatile("//__llsc_futex_xchg\n" > > +" prfm pstl1strm, %2\n" > > +"1: ldxr %w1, %2\n" > > +"2: stlxr %w0, %w4, %2\n" > > +" cbz %w3, 3f\n" > > +" sub %w3, %w3, %w0\n" > > +" cbnz %w3, 1b\n" > > +" mov %w0, %w5\n" > > +"3:\n" > > +" dmb ish\n" > > + _ASM_EXTABLE_UACCESS_ERR(1b, 3b, %w0) > > + _ASM_EXTABLE_UACCESS_ERR(2b, 3b, %w0) > > + : "=&r" (ret), "=&r" (oldval), "+Q" (*uaddr), "+r" (loops) > > + : "r" (oparg), "Ir" (-EAGAIN) > > + : "memory"); > > + uaccess_disable_privileged(); > > + > > + if (!ret) > > + *oval = oldval; > > Hmm, I'm really not sure this is worthwhile. I doubt the "optimisation" > actually does anything and adding a whole new block of asm just for the > SET case isn't much of an improvement on the maintainability side, either. TBH, I had the same question, but I thought this code seems to modify freqenetly, I decide even a small optimisation -- reduce one instruction only. But I don't have strong opinion for this patch. If it's not good for maintainability perspective, This patch can be dropped. Thanks! -- Sincerely, Yeoreum Yun