linux/block/blk-iopoll.c

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/*
* Functions related to interrupt-poll handling in the block layer. This
* is similar to NAPI for network devices.
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/interrupt.h>
#include <linux/cpu.h>
#include <linux/blk-iopoll.h>
#include <linux/delay.h>
#include "blk.h"
static unsigned int blk_iopoll_budget __read_mostly = 256;
static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
/**
* blk_iopoll_sched - Schedule a run of the iopoll handler
* @iop: The parent iopoll structure
*
* Description:
* Add this blk_iopoll structure to the pending poll list and trigger the
* raise of the blk iopoll softirq. The driver must already have gotten a
* successful return from blk_iopoll_sched_prep() before calling this.
**/
void blk_iopoll_sched(struct blk_iopoll *iop)
{
unsigned long flags;
local_irq_save(flags);
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>
2013-10-15 20:22:29 +02:00
list_add_tail(&iop->list, this_cpu_ptr(&blk_cpu_iopoll));
__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
local_irq_restore(flags);
}
EXPORT_SYMBOL(blk_iopoll_sched);
/**
* __blk_iopoll_complete - Mark this @iop as un-polled again
* @iop: The parent iopoll structure
*
* Description:
* See blk_iopoll_complete(). This function must be called with interrupts
* disabled.
**/
void __blk_iopoll_complete(struct blk_iopoll *iop)
{
list_del(&iop->list);
smp_mb__before_atomic();
clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
}
EXPORT_SYMBOL(__blk_iopoll_complete);
/**
* blk_iopoll_complete - Mark this @iop as un-polled again
* @iop: The parent iopoll structure
*
* Description:
* If a driver consumes less than the assigned budget in its run of the
* iopoll handler, it'll end the polled mode by calling this function. The
* iopoll handler will not be invoked again before blk_iopoll_sched_prep()
* is called.
**/
void blk_iopoll_complete(struct blk_iopoll *iop)
{
unsigned long flags;
local_irq_save(flags);
__blk_iopoll_complete(iop);
local_irq_restore(flags);
}
EXPORT_SYMBOL(blk_iopoll_complete);
static void blk_iopoll_softirq(struct softirq_action *h)
{
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>
2013-10-15 20:22:29 +02:00
struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);
int rearm = 0, budget = blk_iopoll_budget;
unsigned long start_time = jiffies;
local_irq_disable();
while (!list_empty(list)) {
struct blk_iopoll *iop;
int work, weight;
/*
* If softirq window is exhausted then punt.
*/
if (budget <= 0 || time_after(jiffies, start_time)) {
rearm = 1;
break;
}
local_irq_enable();
/* Even though interrupts have been re-enabled, this
* access is safe because interrupts can only add new
* entries to the tail of this list, and only ->poll()
* calls can remove this head entry from the list.
*/
iop = list_entry(list->next, struct blk_iopoll, list);
weight = iop->weight;
work = 0;
if (test_bit(IOPOLL_F_SCHED, &iop->state))
work = iop->poll(iop, weight);
budget -= work;
local_irq_disable();
/*
* Drivers must not modify the iopoll state, if they
* consume their assigned weight (or more, some drivers can't
* easily just stop processing, they have to complete an
* entire mask of commands).In such cases this code
* still "owns" the iopoll instance and therefore can
* move the instance around on the list at-will.
*/
if (work >= weight) {
if (blk_iopoll_disable_pending(iop))
__blk_iopoll_complete(iop);
else
list_move_tail(&iop->list, list);
}
}
if (rearm)
__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
local_irq_enable();
}
/**
* blk_iopoll_disable - Disable iopoll on this @iop
* @iop: The parent iopoll structure
*
* Description:
* Disable io polling and wait for any pending callbacks to have completed.
**/
void blk_iopoll_disable(struct blk_iopoll *iop)
{
set_bit(IOPOLL_F_DISABLE, &iop->state);
while (test_and_set_bit(IOPOLL_F_SCHED, &iop->state))
msleep(1);
clear_bit(IOPOLL_F_DISABLE, &iop->state);
}
EXPORT_SYMBOL(blk_iopoll_disable);
/**
* blk_iopoll_enable - Enable iopoll on this @iop
* @iop: The parent iopoll structure
*
* Description:
* Enable iopoll on this @iop. Note that the handler run will not be
* scheduled, it will only mark it as active.
**/
void blk_iopoll_enable(struct blk_iopoll *iop)
{
BUG_ON(!test_bit(IOPOLL_F_SCHED, &iop->state));
smp_mb__before_atomic();
clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
}
EXPORT_SYMBOL(blk_iopoll_enable);
/**
* blk_iopoll_init - Initialize this @iop
* @iop: The parent iopoll structure
* @weight: The default weight (or command completion budget)
* @poll_fn: The handler to invoke
*
* Description:
* Initialize this blk_iopoll structure. Before being actively used, the
* driver must call blk_iopoll_enable().
**/
void blk_iopoll_init(struct blk_iopoll *iop, int weight, blk_iopoll_fn *poll_fn)
{
memset(iop, 0, sizeof(*iop));
INIT_LIST_HEAD(&iop->list);
iop->weight = weight;
iop->poll = poll_fn;
set_bit(IOPOLL_F_SCHED, &iop->state);
}
EXPORT_SYMBOL(blk_iopoll_init);
static int blk_iopoll_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
/*
* If a CPU goes away, splice its entries to the current CPU
* and trigger a run of the softirq
*/
if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
int cpu = (unsigned long) hcpu;
local_irq_disable();
list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
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>
2013-10-15 20:22:29 +02:00
this_cpu_ptr(&blk_cpu_iopoll));
__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
local_irq_enable();
}
return NOTIFY_OK;
}
static struct notifier_block blk_iopoll_cpu_notifier = {
.notifier_call = blk_iopoll_cpu_notify,
};
static __init int blk_iopoll_setup(void)
{
int i;
for_each_possible_cpu(i)
INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
open_softirq(BLOCK_IOPOLL_SOFTIRQ, blk_iopoll_softirq);
register_hotcpu_notifier(&blk_iopoll_cpu_notifier);
return 0;
}
subsys_initcall(blk_iopoll_setup);