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arch/Timer: Make sure ARCH_TIMER_FREQ is a power of two

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(avoid division and modulo, division is slow)
Fortunately, GCC will optimize divisions by powers of two to simple bitwise shifts :)
This commit is contained in:
apio 2023-01-16 19:43:05 +01:00
parent d0600f5714
commit 1b807a4e06
Signed by: asleepymoon
GPG Key ID: B8A7D06E42258954
2 changed files with 6 additions and 3 deletions
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7
kernel/src/arch/Timer.cpp
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@ -2,8 +2,10 @@
#include "Log.h" #include "Log.h"
#include "arch/Serial.h" #include "arch/Serial.h"
#include "boot/bootboot.h" #include "boot/bootboot.h"
#include <luna/TypeTraits.h>
// FIXME: Storing these values as unsigned integers doesn't allow for pre-epoch times. // NOTE: Storing these values as unsigned integers doesn't allow for pre-epoch times.
// We are in 2023 anyway, not sure why anybody would want to set their computer's time to 1945.
static u64 timer_ticks = 0; static u64 timer_ticks = 0;
static u64 boot_timestamp; static u64 boot_timestamp;
@ -134,8 +136,9 @@ namespace Timer
} }
} }
static_assert(IsPowerOfTwo<usize, ARCH_TIMER_FREQ>, "ARCH_TIMER_FREQ must be a power of two");
bool should_invoke_scheduler() bool should_invoke_scheduler()
{ {
// FIXME: Modulo is SLOW. We're calling this every tick.
return (timer_ticks % ARCH_TIMER_FREQ) == 0; return (timer_ticks % ARCH_TIMER_FREQ) == 0;
} }

2
kernel/src/arch/x86_64/Timer.h
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@ -1,4 +1,4 @@
#pragma once #pragma once
#include <luna/Types.h> #include <luna/Types.h>
const usize ARCH_TIMER_FREQ = 5; const usize ARCH_TIMER_FREQ = 4;