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std.atomic: Implement specialized spinLoopHint() for more architectures.

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Alex Rønne Petersen 2024-07-27 12:03:05 +02:00
parent 5b68595255
commit 9d23e711ef
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1 changed files with 32 additions and 4 deletions
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36
lib/std/atomic.zig
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@ -378,21 +378,33 @@ pub inline fn spinLoopHint() void {
// No-op instruction that can hint to save (or share with a hardware-thread)
// pipelining/power resources
// https://software.intel.com/content/www/us/en/develop/articles/benefitting-power-and-performance-sleep-loops.html
.x86, .x86_64 => asm volatile ("pause" ::: "memory"),
.x86,
.x86_64,
=> asm volatile ("pause" ::: "memory"),
// No-op instruction that serves as a hardware-thread resource yield hint.
// https://stackoverflow.com/a/7588941
.powerpc64, .powerpc64le => asm volatile ("or 27, 27, 27" ::: "memory"),
.powerpc,
.powerpcle,
.powerpc64,
.powerpc64le,
=> asm volatile ("or 27, 27, 27" ::: "memory"),
// `isb` appears more reliable for releasing execution resources than `yield`
// on common aarch64 CPUs.
// https://bugs.java.com/bugdatabase/view_bug.do?bug_id=8258604
// https://bugs.mysql.com/bug.php?id=100664
.aarch64, .aarch64_be => asm volatile ("isb" ::: "memory"),
.aarch64,
.aarch64_be,
=> asm volatile ("isb" ::: "memory"),
// `yield` was introduced in v6k but is also available on v6m.
// https://www.keil.com/support/man/docs/armasm/armasm_dom1361289926796.htm
.arm, .armeb, .thumb, .thumbeb => {
.arm,
.armeb,
.thumb,
.thumbeb,
=> {
const can_yield = comptime std.Target.arm.featureSetHasAny(builtin.target.cpu.features, .{
.has_v6k, .has_v6m,
});
@ -402,6 +414,22 @@ pub inline fn spinLoopHint() void {
asm volatile ("" ::: "memory");
}
},
// The 8-bit immediate specifies the amount of cycles to pause for. We can't really be too
// opinionated here.
.hexagon,
=> asm volatile ("pause(#1)" ::: "memory"),
.riscv32,
.riscv64,
=> {
if (comptime std.Target.riscv.featureSetHas(builtin.target.cpu.features, .zihintpause)) {
asm volatile ("pause" ::: "memory");
} else {
asm volatile ("" ::: "memory");
}
},
// Memory barrier to prevent the compiler from optimizing away the spin-loop
// even if no hint_instruction was provided.
else => asm volatile ("" ::: "memory"),