9fd9f80431
rtm wrote: > Why does acquire() call cpuid()? Why does release() call cpuid()? The cpuid in acquire is redundant with the cmpxchg, as you said. I have removed the cpuid from acquire. The cpuid in release is actually doing something important, but not on the hardware. It keeps gcc from reordering the lock->locked assignment above the other two during optimization. (Not that current gcc -O2 would choose to do that, but it is allowed to.) I have replaced the cpuid in release with a "gcc barrier" that keeps gcc from moving things around but has no hardware effect. On a related note, I don't think the cpuid in mpmain is necessary, for the same reason that the cpuid wasn't needed in release. As to the question of whether acquire(); x = protected; release(); might read protected after release(), I still haven't convinced myself whether it can. I'll put the cpuid back into release if we determine that it can. Russ
85 lines
2 KiB
C
85 lines
2 KiB
C
#include "types.h"
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#include "defs.h"
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#include "param.h"
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#include "mmu.h"
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#include "proc.h"
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#include "x86.h"
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static void bootothers(void);
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static void mpmain(void) __attribute__((noreturn));
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// Bootstrap processor starts running C code here.
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int
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main(void)
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{
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extern char edata[], end[];
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// clear BSS
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memset(edata, 0, end - edata);
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mp_init(); // collect info about this machine
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lapic_init(mp_bcpu());
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cprintf("\ncpu%d: starting xv6\n\n", cpu());
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pinit(); // process table
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binit(); // buffer cache
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pic_init(); // interrupt controller
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ioapic_init(); // another interrupt controller
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kinit(); // physical memory allocator
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tvinit(); // trap vectors
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fileinit(); // file table
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iinit(); // inode cache
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console_init(); // I/O devices & their interrupts
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ide_init(); // disk
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if(!ismp)
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timer_init(); // uniprocessor timer
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userinit(); // first user process
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bootothers(); // start other processors
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// Finish setting up this processor in mpmain.
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mpmain();
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}
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// Bootstrap processor gets here after setting up the hardware.
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// Additional processors start here.
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static void
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mpmain(void)
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{
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cprintf("cpu%d: mpmain\n", cpu());
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idtinit();
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if(cpu() != mp_bcpu())
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lapic_init(cpu());
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setupsegs(0);
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cpus[cpu()].booted = 1;
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scheduler();
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}
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static void
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bootothers(void)
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{
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extern uchar _binary_bootother_start[], _binary_bootother_size[];
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uchar *code;
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struct cpu *c;
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char *stack;
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// Write bootstrap code to unused memory at 0x7000.
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code = (uchar*)0x7000;
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memmove(code, _binary_bootother_start, (uint)_binary_bootother_size);
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for(c = cpus; c < cpus+ncpu; c++){
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if(c == cpus+cpu()) // We've started already.
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continue;
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// Fill in %esp, %eip and start code on cpu.
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stack = kalloc(KSTACKSIZE);
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*(void**)(code-4) = stack + KSTACKSIZE;
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*(void**)(code-8) = mpmain;
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lapic_startap(c->apicid, (uint)code);
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// Wait for cpu to get through bootstrap.
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while(c->booted == 0)
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;
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}
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}
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