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SubjectRe: [PATCH] percpu updates
Andrew Morton wrote:
> Brian Gerst wrote:
>
>>These patches convert some of the existing arrays based on NR_CPUS to
>>use the new per cpu code.
>>
>
>
> Brian, I tested this patch (rediffed against 2.5.13, below)
> on the quad Xeon and it failed.
>
> The machine died when bringing up the secondary CPUs
> ("CPU#3 already started!" and "Unable to handle kernel...")
>
> I backed out the sched.c part and the machine booted. So
> I guess the secondary CPU bringup code uses the scheduler
> somehow.
>
> And again, the numbers in /proc/meminfo are whacko:
>
> LowFree: 94724 kB
> SwapTotal: 4000040 kB
> SwapFree: 3999700 kB
> Dirty: 7232 kB
> Writeback: 4294967264 kB
>
> Which never happens with the open-coded per-cpu accumulators.
> After a normal boot I see:
>
> LowFree: 95804 kB
> SwapTotal: 4000040 kB
> SwapFree: 3999940 kB
> Dirty: 1356 kB
> Writeback: 0 kB
>
>
> Now, it may be that some pages are being marked dirty before
> the per-cpu areas are set up, but there's no way in which
> any pages will have been marked for writeback by that time, so
> that "-32" value is definitely wrong.
>
> 'fraid I have to do a whine-and-run on this problem, but
> it does still appear that there is something fishy with
> the percpu infrastructure.
>

Andrew, could you try this patch? I suspect something in setup_arch()
is touching the per cpu area before it gets copied for the other cpus.
This patch makes certain the boot cpu area is setup ASAP.
--

Brian Gerst
diff -urN linux-2.5.13/arch/i386/vmlinux.lds linux/arch/i386/vmlinux.lds
--- linux-2.5.13/arch/i386/vmlinux.lds Thu Mar 7 21:18:16 2002
+++ linux/arch/i386/vmlinux.lds Sun May 5 11:46:26 2002
@@ -57,10 +57,13 @@
*(.initcall7.init)
}
__initcall_end = .;
+
. = ALIGN(32);
__per_cpu_start = .;
.data.percpu : { *(.data.percpu) }
+ . = ALIGN(32);
__per_cpu_end = .;
+
. = ALIGN(4096);
__init_end = .;

@@ -70,6 +73,10 @@
. = ALIGN(32);
.data.cacheline_aligned : { *(.data.cacheline_aligned) }

+ . = ALIGN(32);
+ __cpu0_data = .;
+ .data.cpu0 : { . += SIZEOF(.data.percpu); }
+
__bss_start = .; /* BSS */
.bss : {
*(.bss)
diff -urN linux-2.5.13/init/main.c linux/init/main.c
--- linux-2.5.13/init/main.c Wed May 1 08:40:14 2002
+++ linux/init/main.c Sun May 5 12:27:38 2002
@@ -272,28 +272,40 @@
#define smp_init() do { } while (0)
#endif

+static inline void setup_boot_cpu_area(void) { }
static inline void setup_per_cpu_areas(void) { }

#else

#ifdef __GENERIC_PER_CPU
+/* Created by linker magic */
+extern char __per_cpu_start[], __per_cpu_end[], __cpu0_data[];
unsigned long __per_cpu_offset[NR_CPUS];

+static void __init setup_boot_cpu_area(void)
+{
+ unsigned long size;
+
+ size = __per_cpu_end - __per_cpu_start;
+ if (!size)
+ return;
+ __per_cpu_offset[0] = __cpu0_data - __per_cpu_start;
+ memcpy(__cpu0_data, __per_cpu_start, size);
+}
+
static void __init setup_per_cpu_areas(void)
{
unsigned long size, i;
char *ptr;
- /* Created by linker magic */
- extern char __per_cpu_start[], __per_cpu_end[];

/* Copy section for each CPU (we discard the original) */
- size = ALIGN(__per_cpu_end - __per_cpu_start, SMP_CACHE_BYTES);
+ size = __per_cpu_end - __per_cpu_start;
if (!size)
return;

ptr = alloc_bootmem(size * NR_CPUS);

- for (i = 0; i < NR_CPUS; i++, ptr += size) {
+ for (i = 1; i < NR_CPUS; i++, ptr += size) {
__per_cpu_offset[i] = ptr - __per_cpu_start;
memcpy(ptr, __per_cpu_start, size);
}
@@ -340,6 +352,7 @@
* enable them
*/
lock_kernel();
+ setup_boot_cpu_area();
printk(linux_banner);
setup_arch(&command_line);
setup_per_cpu_areas();
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