Re: [patch 05/14] percpu: Use a Kconfig variable to configure arch specific percpu setup

Christoph Lameter
2007-11-29T06:10:48Z

Second portion. Add a new seg_offset macro to calculate the offset. This
can be avoided if the linker relocates the per cpu area to zero. Includes
a patch to read trickle count via both methods to verify that it actually
works. Both patches on top of the per cpu cleanup patches that I sent
today too.

x86_64: Make the x86_32 percpu operations usable on x86_64

Calculate the offset relative to gs in order to be able to address
per cpu data using the x86_64 per cpu macros.

The subtraction of __per_cpu_start will make the offset based
from the beginning of the per cpu area. That is where gs points to.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
drivers/char/random.c | 2 +-
include/asm-x86/percpu.h | 29 ++++++++++++++++++-----------
init/main.c | 5 +++++
3 files changed, 24 insertions(+), 12 deletions(-)

Index: linux-2.6.24-rc3-mm2/include/asm-x86/percpu.h
===================================================================
--- linux-2.6.24-rc3-mm2.orig/include/asm-x86/percpu.h 2007-11-28 17:50:01.861182410 -0800
+++ linux-2.6.24-rc3-mm2/include/asm-x86/percpu.h 2007-11-28 21:22:50.845872906 -0800
@@ -16,7 +16,13 @@
#define __my_cpu_offset read_pda(data_offset)

#define per_cpu_offset(x) (__per_cpu_offset(x))
+#define __percpu_seg "%%gs:"
+/* Calculate the offset to use with the segment register */
+#define seg_offset(name) (*SHIFT_PTR(&per_cpu_var(name), - (unsigned long)__per_cpu_start))

+#else
+#define __percpu_seg ""
+#define seg_offset(name) per_cpu_var(name)
#endif
#include <asm-generic/percpu.h>

@@ -64,16 +70,11 @@ DECLARE_PER_CPU(struct x8664_pda, pda);
* PER_CPU(cpu_gdt_descr, %ebx)
*/
#ifdef CONFIG_SMP
-
#define __my_cpu_offset x86_read_percpu(this_cpu_off)
-
/* fs segment starts at (positive) offset == __per_cpu_offset[cpu] */
#define __percpu_seg "%%fs:"
-
#else /* !SMP */
-
#define __percpu_seg ""
-
#endif /* SMP */

#include <asm-generic/percpu.h>
@@ -81,6 +82,13 @@ DECLARE_PER_CPU(struct x8664_pda, pda);
/* We can use this directly for local CPU (faster). */
DECLARE_PER_CPU(unsigned long, this_cpu_off);

+#define seg_offset(name) per_cpu_var(name)
+
+#endif /* __ASSEMBLY__ */
+#endif /* !CONFIG_X86_64 */
+
+#ifndef __ASSEMBLY__
+
/* For arch-specific code, we can use direct single-insn ops (they
* don't give an lvalue though). */
extern void __bad_percpu_size(void);
@@ -132,11 +140,10 @@ extern void __bad_percpu_size(void);
} \
ret__; })

-#define x86_read_percpu(var) percpu_from_op("mov", per_cpu__##var)
-#define x86_write_percpu(var,val) percpu_to_op("mov", per_cpu__##var, val)
-#define x86_add_percpu(var,val) percpu_to_op("add", per_cpu__##var, val)
-#define x86_sub_percpu(var,val) percpu_to_op("sub", per_cpu__##var, val)
-#define x86_or_percpu(var,val) percpu_to_op("or", per_cpu__##var, val)
+#define x86_read_percpu(var) percpu_from_op("mov", seg_offset(var))
+#define x86_write_percpu(var,val) percpu_to_op("mov", seg_offset(var), val)
+#define x86_add_percpu(var,val) percpu_to_op("add", seg_offset(var), val)
+#define x86_sub_percpu(var,val) percpu_to_op("sub", seg_offset(var), val)
+#define x86_or_percpu(var,val) percpu_to_op("or", seg_offset(var), val)
#endif /* !__ASSEMBLY__ */
-#endif /* !CONFIG_X86_64 */
#endif /* _ASM_X86_PERCPU_H_ */
Index: linux-2.6.24-rc3-mm2/drivers/char/random.c
===================================================================
--- linux-2.6.24-rc3-mm2.orig/drivers/char/random.c 2007-11-28 21:20:58.225804398 -0800
+++ linux-2.6.24-rc3-mm2/drivers/char/random.c 2007-11-28 21:28:38.967363573 -0800
@@ -272,7 +272,7 @@ static int random_write_wakeup_thresh =

static int trickle_thresh __read_mostly = INPUT_POOL_WORDS * 28;

-static DEFINE_PER_CPU(int, trickle_count) = 0;
+DEFINE_PER_CPU(int, trickle_count) = 55;

/*
* A pool of size .poolwords is stirred with a primitive polynomial
Index: linux-2.6.24-rc3-mm2/init/main.c
===================================================================
--- linux-2.6.24-rc3-mm2.orig/init/main.c 2007-11-28 21:10:54.245804225 -0800
+++ linux-2.6.24-rc3-mm2/init/main.c 2007-11-28 21:22:17.769053628 -0800
@@ -504,6 +504,8 @@ void __init __attribute__((weak)) smp_se
{
}

+DECLARE_PER_CPU(int, trickle_count);
+
asmlinkage void __init start_kernel(void)
{
char * command_line;
@@ -645,6 +647,9 @@ asmlinkage void __init start_kernel(void

acpi_early_init(); /* before LAPIC and SMP init */

+ printk("Reading trickle cound =%lu. Is %lu\n",
+ x86_read_percpu(trickle_count),
+ __raw_get_cpu_var(trickle_count));
/* Do the rest non-__init'ed, we're now alive */
rest_init();
}