In message <3C57207E.28598C1F@zip.com.au> you write:
> Rusty Russell wrote:
> > Yes. But for a large amount of code it doesn't matter, and most
> > architectures don't know how many CPUs there are before smp_init().
> > Of course, we could make it NR_CPUS...
>
> I don't think there's a need. You can use .data.percpu directly
> for the boot CPU, dynamically allocate storage for the others.
> This actually saves one CPU's worth of memory :)
No it doesn't: we discard the original anyway (it's within the init
section). You also destroy the "derive smp_processor_id from per-cpu
pointer register" idea by making them non-contiguous.
> unsigned long __per_cpu_offset[NR_CPUS] = { (unsigned long *)&__per_cpu_star
t, };
>
> Then each CPU has, at all times, a valid personal __per_cpu_offset[]
> entry. The only restriction is that the boot CPU cannot
> touch other CPU's per-cpu data before those CPUs are brought
> up.
You still can't use anything like the slab allocator in
eg. cpu_init(), which is inviting trouble. I think we really are best
off allocating up front and avoiding this whole mess. Patch below
(no, it won't boot at the moment, since the per_cpu area will be size
0, and that hits a BUG() in alloc_bootmem, but if you put something in
it it works).
Other patches to follow...
Rusty.
diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.3-pre6/arch/i386/vmlinux.lds working-2.5.3-pre6-percpu/arch/i386/vmlinux.lds
--- linux-2.5.3-pre6/arch/i386/vmlinux.lds Tue Jan 29 09:16:52 2002
+++ working-2.5.3-pre6-percpu/arch/i386/vmlinux.lds Wed Jan 30 10:17:38 2002
@@ -58,6 +58,10 @@
*(.initcall7.init)
}
__initcall_end = .;
+ . = ALIGN(32);
+ __per_cpu_start = .;
+ .data.percpu : { *(.data.percpu) }
+ __per_cpu_end = .;
. = ALIGN(4096);
__init_end = .;
diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.3-pre6/arch/ppc/vmlinux.lds working-2.5.3-pre6-percpu/arch/ppc/vmlinux.lds
--- linux-2.5.3-pre6/arch/ppc/vmlinux.lds Tue Jan 29 09:16:53 2002
+++ working-2.5.3-pre6-percpu/arch/ppc/vmlinux.lds Wed Jan 30 10:17:38 2002
@@ -104,6 +104,10 @@
*(.initcall7.init)
}
__initcall_end = .;
+ . = ALIGN(32);
+ __per_cpu_start = .;
+ .data.percpu : { *(.data.percpu) }
+ __per_cpu_end = .;
. = ALIGN(4096);
__init_end = .;
diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.3-pre6/include/linux/smp.h working-2.5.3-pre6-percpu/include/linux/smp.h
--- linux-2.5.3-pre6/include/linux/smp.h Thu Jan 17 16:35:24 2002
+++ working-2.5.3-pre6-percpu/include/linux/smp.h Wed Jan 30 10:17:38 2002
@@ -71,7 +71,17 @@
#define MSG_RESCHEDULE 0x0003 /* Reschedule request from master CPU*/
#define MSG_CALL_FUNCTION 0x0004 /* Call function on all other CPUs */
-#else
+#define __per_cpu_data __attribute__((section(".data.percpu")))
+
+#ifndef __HAVE_ARCH_CPU_OFFSET
+#define per_cpu_offset(cpu) (__per_cpu_offset[(cpu)])
+#endif
+
+#define per_cpu(var, cpu) \
+(*(__typeof__(&var)((void *)&var + per_cpu_offset(cpu))))
+
+extern unsigned long __per_cpu_offset[NR_CPUS];
+#else /* !SMP */
/*
* These macros fold the SMP functionality into a single CPU system
@@ -88,6 +98,10 @@
#define cpu_online_map 1
static inline void smp_send_reschedule(int cpu) { }
static inline void smp_send_reschedule_all(void) { }
+#define __per_cpu_data
+#define per_cpu(var, cpu) var
#endif
+
+#define this_cpu(var) per_cpu(var,smp_processor_id())
#endif
diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.3-pre6/init/main.c working-2.5.3-pre6-percpu/init/main.c
--- linux-2.5.3-pre6/init/main.c Tue Jan 29 09:17:09 2002
+++ working-2.5.3-pre6-percpu/init/main.c Wed Jan 30 10:43:33 2002
@@ -272,8 +272,33 @@
#define smp_init() do { } while (0)
#endif
+static inline void setup_per_cpu_areas(void)
+{
+}
#else
+unsigned long __per_cpu_offset[NR_CPUS];
+/* Created by linker magic */
+extern char __per_cpu_start, __per_cpu_end;
+
+static void setup_per_cpu_areas(void)
+{
+ unsigned int i;
+ size_t per_cpu_size;
+ char *region;
+
+ /* Set up per-CPU offset pointers. Page align to be safe. */
+ per_cpu_size = ((&__per_cpu_end - &__per_cpu_start) + PAGE_SIZE-1)
+ & ~(PAGE_SIZE-1);
+ region = alloc_bootmem_pages(per_cpu_size*NR_CPUS);
+ for (i = 0; i < NR_CPUS; i++) {
+ memcpy(region + per_cpu_size*i, &__per_cpu_start,
+ &__per_cpu_end - &__per_cpu_start);
+ __per_cpu_offset[i]
+ = (region + per_cpu_size*i) - &__per_cpu_start;
+ }
+}
+
/* Called by boot processor to activate the rest. */
static void __init smp_init(void)
{
@@ -316,6 +341,7 @@
lock_kernel();
printk(linux_banner);
setup_arch(&command_line);
+ setup_per_cpu_areas();
printk("Kernel command line: %s\n", saved_command_line);
parse_options(command_line);
trap_init();
-- Anyone who quotes me in their sig is an idiot. -- Rusty Russell. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Thu Jan 31 2002 - 21:01:10 EST