forked from Minki/linux
494fc42170
__get_cpu_var() is used for multiple purposes in the kernel source. One of
them is address calculation via the form &__get_cpu_var(x). This calculates
the address for the instance of the percpu variable of the current processor
based on an offset.
Other use cases are for storing and retrieving data from the current
processors percpu area. __get_cpu_var() can be used as an lvalue when
writing data or on the right side of an assignment.
__get_cpu_var() is defined as :
#define __get_cpu_var(var) (*this_cpu_ptr(&(var)))
__get_cpu_var() always only does an address determination. However, store
and retrieve operations could use a segment prefix (or global register on
other platforms) to avoid the address calculation.
this_cpu_write() and this_cpu_read() can directly take an offset into a
percpu area and use optimized assembly code to read and write per cpu
variables.
This patch converts __get_cpu_var into either an explicit address
calculation using this_cpu_ptr() or into a use of this_cpu operations that
use the offset. Thereby address calculations are avoided and less registers
are used when code is generated.
At the end of the patch set all uses of __get_cpu_var have been removed so
the macro is removed too.
The patch set includes passes over all arches as well. Once these operations
are used throughout then specialized macros can be defined in non -x86
arches as well in order to optimize per cpu access by f.e. using a global
register that may be set to the per cpu base.
Transformations done to __get_cpu_var()
1. Determine the address of the percpu instance of the current processor.
DEFINE_PER_CPU(int, y);
int *x = &__get_cpu_var(y);
Converts to
int *x = this_cpu_ptr(&y);
2. Same as #1 but this time an array structure is involved.
DEFINE_PER_CPU(int, y[20]);
int *x = __get_cpu_var(y);
Converts to
int *x = this_cpu_ptr(y);
3. Retrieve the content of the current processors instance of a per cpu
variable.
DEFINE_PER_CPU(int, y);
int x = __get_cpu_var(y)
Converts to
int x = __this_cpu_read(y);
4. Retrieve the content of a percpu struct
DEFINE_PER_CPU(struct mystruct, y);
struct mystruct x = __get_cpu_var(y);
Converts to
memcpy(&x, this_cpu_ptr(&y), sizeof(x));
5. Assignment to a per cpu variable
DEFINE_PER_CPU(int, y)
__get_cpu_var(y) = x;
Converts to
__this_cpu_write(y, x);
6. Increment/Decrement etc of a per cpu variable
DEFINE_PER_CPU(int, y);
__get_cpu_var(y)++
Converts to
__this_cpu_inc(y)
Cc: sparclinux@vger.kernel.org
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
40 lines
945 B
C
40 lines
945 B
C
/* cpudata.h: Per-cpu parameters.
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*
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* Copyright (C) 2003, 2005, 2006 David S. Miller (davem@davemloft.net)
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*/
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#ifndef _SPARC64_CPUDATA_H
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#define _SPARC64_CPUDATA_H
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#ifndef __ASSEMBLY__
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typedef struct {
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/* Dcache line 1 */
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unsigned int __softirq_pending; /* must be 1st, see rtrap.S */
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unsigned int __nmi_count;
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unsigned long clock_tick; /* %tick's per second */
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unsigned long __pad;
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unsigned int irq0_irqs;
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unsigned int __pad2;
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/* Dcache line 2, rarely used */
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unsigned int dcache_size;
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unsigned int dcache_line_size;
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unsigned int icache_size;
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unsigned int icache_line_size;
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unsigned int ecache_size;
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unsigned int ecache_line_size;
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int core_id;
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int proc_id;
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} cpuinfo_sparc;
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DECLARE_PER_CPU(cpuinfo_sparc, __cpu_data);
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#define cpu_data(__cpu) per_cpu(__cpu_data, (__cpu))
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#define local_cpu_data() (*this_cpu_ptr(&__cpu_data))
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#endif /* !(__ASSEMBLY__) */
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#include <asm/trap_block.h>
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#endif /* _SPARC64_CPUDATA_H */
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