linux/block/blk-iopoll.c
Jens Axboe 89f8b33ca1 block: remove old blk_iopoll_enabled variable
This was a debugging measure to toggle enabled/disabled
when testing. But for real production setups, it's not
safe to toggle this setting without either reloading
drivers of quiescing IO first. Neither of which the toggle
enforces.

Additionally, it makes drivers deal with the conditional
state.

Remove it completely. It's up to the driver whether iopoll
is enabled or not.

Signed-off-by: Jens Axboe <axboe@fb.com>
2014-03-13 09:38:42 -06:00

225 lines
5.9 KiB
C

/*
* 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);
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_clear_bit();
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 *iopoll)
{
unsigned long flags;
local_irq_save(flags);
__blk_iopoll_complete(iopoll);
local_irq_restore(flags);
}
EXPORT_SYMBOL(blk_iopoll_complete);
static void blk_iopoll_softirq(struct softirq_action *h)
{
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_clear_bit();
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),
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);