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rp: optimize rom-func-cache for runtime

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storing a full function pointer initialized to a resolver trampoline
lets us avoid the runtime cost of checking whether we need to do the
initialization.
This commit is contained in:
pennae 2023-04-19 21:56:18 +02:00
parent 41e90e22e2
commit 837cdacd16
1 changed files with 55 additions and 62 deletions
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117
embassy-rp/src/rom_data.rs
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@ -56,50 +56,11 @@ macro_rules! declare_rom_function {
fn $name:ident( $($argname:ident: $ty:ty),* ) -> $ret:ty
$lookup:block
) => {
#[doc = r"Additional access for the `"]
#[doc = stringify!($name)]
#[doc = r"` ROM function."]
pub mod $name {
/// Retrieve a function pointer.
#[cfg(not(feature = "rom-func-cache"))]
pub fn ptr() -> extern "C" fn( $($argname: $ty),* ) -> $ret {
let p: *const u32 = $lookup;
unsafe {
let func : extern "C" fn( $($argname: $ty),* ) -> $ret = core::mem::transmute(p);
func
}
}
/// Retrieve a function pointer.
#[cfg(feature = "rom-func-cache")]
pub fn ptr() -> extern "C" fn( $($argname: $ty),* ) -> $ret {
use core::sync::atomic::{AtomicU16, Ordering};
// All pointers in the ROM fit in 16 bits, so we don't need a
// full width word to store the cached value.
static CACHED_PTR: AtomicU16 = AtomicU16::new(0);
// This is safe because the lookup will always resolve
// to the same value. So even if an interrupt or another
// core starts at the same time, it just repeats some
// work and eventually writes back the correct value.
let p: *const u32 = match CACHED_PTR.load(Ordering::Relaxed) {
0 => {
let raw: *const u32 = $lookup;
CACHED_PTR.store(raw as u16, Ordering::Relaxed);
raw
},
val => val as *const u32,
};
unsafe {
let func : extern "C" fn( $($argname: $ty),* ) -> $ret = core::mem::transmute(p);
func
}
}
}
$(#[$outer])*
pub extern "C" fn $name( $($argname: $ty),* ) -> $ret {
$name::ptr()($($argname),*)
declare_rom_function!{
__internal ,
$(#[$outer])*
fn $name( $($argname: $ty),* ) -> $ret
$lookup
}
};
@ -107,6 +68,21 @@ macro_rules! declare_rom_function {
$(#[$outer:meta])*
unsafe fn $name:ident( $($argname:ident: $ty:ty),* ) -> $ret:ty
$lookup:block
) => {
declare_rom_function!{
__internal unsafe ,
$(#[$outer])*
fn $name( $($argname: $ty),* ) -> $ret
$lookup
}
};
(
__internal
$( $maybe_unsafe:ident )? ,
$(#[$outer:meta])*
fn $name:ident( $($argname:ident: $ty:ty),* ) -> $ret:ty
$lookup:block
) => {
#[doc = r"Additional access for the `"]
#[doc = stringify!($name)]
@ -114,43 +90,58 @@ macro_rules! declare_rom_function {
pub mod $name {
/// Retrieve a function pointer.
#[cfg(not(feature = "rom-func-cache"))]
pub fn ptr() -> unsafe extern "C" fn( $($argname: $ty),* ) -> $ret {
pub fn ptr() -> $( $maybe_unsafe )? extern "C" fn( $($argname: $ty),* ) -> $ret {
let p: *const u32 = $lookup;
unsafe {
let func : unsafe extern "C" fn( $($argname: $ty),* ) -> $ret = core::mem::transmute(p);
let func : $( $maybe_unsafe )? extern "C" fn( $($argname: $ty),* ) -> $ret
= core::mem::transmute(p);
func
}
}
#[cfg(feature = "rom-func-cache")]
// unlike rp2040-hal we store a full word, containing the full function pointer.
// rp2040-hal saves two bytes by storing only the rom offset, at the cost of
// having to do an indirection and an atomic operation on every rom call.
static mut CACHE: $( $maybe_unsafe )? extern "C" fn( $($argname: $ty),* ) -> $ret
= trampoline;
#[cfg(feature = "rom-func-cache")]
$( $maybe_unsafe )? extern "C" fn trampoline( $($argname: $ty),* ) -> $ret {
use core::sync::atomic::{compiler_fence, Ordering};
let p: *const u32 = $lookup;
#[allow(unused_unsafe)]
unsafe {
CACHE = core::mem::transmute(p);
compiler_fence(Ordering::Release);
CACHE($($argname),*)
}
}
/// Retrieve a function pointer.
#[cfg(feature = "rom-func-cache")]
pub fn ptr() -> unsafe extern "C" fn( $($argname: $ty),* ) -> $ret {
use core::sync::atomic::{AtomicU16, Ordering};
pub fn ptr() -> $( $maybe_unsafe )? extern "C" fn( $($argname: $ty),* ) -> $ret {
use core::sync::atomic::{compiler_fence, Ordering};
// All pointers in the ROM fit in 16 bits, so we don't need a
// full width word to store the cached value.
static CACHED_PTR: AtomicU16 = AtomicU16::new(0);
// This is safe because the lookup will always resolve
// to the same value. So even if an interrupt or another
// core starts at the same time, it just repeats some
// work and eventually writes back the correct value.
let p: *const u32 = match CACHED_PTR.load(Ordering::Relaxed) {
0 => {
let raw: *const u32 = $lookup;
CACHED_PTR.store(raw as u16, Ordering::Relaxed);
raw
},
val => val as *const u32,
};
//
// We easily get away with using only compiler fences here
// because RP2040 SRAM is not cached. If it were we'd need
// to make sure updates propagate quickly, or just take the
// hit and let each core resolve every function once.
compiler_fence(Ordering::Acquire);
unsafe {
let func : unsafe extern "C" fn( $($argname: $ty),* ) -> $ret = core::mem::transmute(p);
func
CACHE
}
}
}
$(#[$outer])*
pub unsafe extern "C" fn $name( $($argname: $ty),* ) -> $ret {
pub $( $maybe_unsafe )? extern "C" fn $name( $($argname: $ty),* ) -> $ret {
$name::ptr()($($argname),*)
}
};
@ -369,6 +360,7 @@ pub fn fplib_start() -> *const u8 {
}
/// See Table 180 in the RP2040 datasheet for the contents of this table.
#[cfg_attr(feature = "rom-func-cache", inline(never))]
pub fn soft_float_table() -> *const usize {
rom_table_lookup(DATA_TABLE, *b"SF")
}
@ -379,6 +371,7 @@ pub fn fplib_end() -> *const u8 {
}
/// This entry is only present in the V2 bootrom. See Table 182 in the RP2040 datasheet for the contents of this table.
#[cfg_attr(feature = "rom-func-cache", inline(never))]
pub fn soft_double_table() -> *const usize {
if rom_version_number() < 2 {
panic!(