path: root/block/blk-softirq.c
diff options
authorChristoph Lameter <cl@linux.com>2013-10-15 12:22:29 -0600
committerJens Axboe <axboe@kernel.dk>2013-11-08 08:59:58 -0700
commit170d800af83f3ab2b5ced0e370a861e023dee22a (patch)
treebcb9225dbb73e641f74ef20ec1e7aff03667e18b /block/blk-softirq.c
parent8077c0d983ab276ec5f2700df56a64d671781905 (diff)
block: Replace __get_cpu_var uses
__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) Signed-off-by: Christoph Lameter <cl@linux.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-softirq.c')
1 files changed, 4 insertions, 4 deletions
diff --git a/block/blk-softirq.c b/block/blk-softirq.c
index ec9e60636f43..ce4b8bfd3d27 100644
--- a/block/blk-softirq.c
+++ b/block/blk-softirq.c
@@ -23,7 +23,7 @@ static void blk_done_softirq(struct softirq_action *h)
struct list_head *cpu_list, local_list;
- cpu_list = &__get_cpu_var(blk_cpu_done);
+ cpu_list = this_cpu_ptr(&blk_cpu_done);
list_replace_init(cpu_list, &local_list);
@@ -44,7 +44,7 @@ static void trigger_softirq(void *data)
struct list_head *list;
- list = &__get_cpu_var(blk_cpu_done);
+ list = this_cpu_ptr(&blk_cpu_done);
list_add_tail(&rq->csd.list, list);
if (list->next == &rq->csd.list)
@@ -90,7 +90,7 @@ static int blk_cpu_notify(struct notifier_block *self, unsigned long action,
list_splice_init(&per_cpu(blk_cpu_done, cpu),
- &__get_cpu_var(blk_cpu_done));
+ this_cpu_ptr(&blk_cpu_done));
@@ -135,7 +135,7 @@ void __blk_complete_request(struct request *req)
if (ccpu == cpu || shared) {
struct list_head *list;
- list = &__get_cpu_var(blk_cpu_done);
+ list = this_cpu_ptr(&blk_cpu_done);
list_add_tail(&req->csd.list, list);