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workqueue: introduce WORK_OFFQ_FLAG_*

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Low WORK_STRUCT_FLAG_BITS bits of work_struct->data contain
WORK_STRUCT_FLAG_* and flush color.  If the work item is queued, the
rest point to the cpu_workqueue with WORK_STRUCT_CWQ set; otherwise,
WORK_STRUCT_CWQ is clear and the bits contain the last CPU number -
either a real CPU number or one of WORK_CPU_*.

Scheduled addition of mod_delayed_work[_on]() requires an additional
flag, which is used only while a work item is off queue.  There are
more than enough bits to represent off-queue CPU number on both 32 and
64bits.  This patch introduces WORK_OFFQ_FLAG_* which occupy the lower
part of the @work->data high bits while off queue.  This patch doesn't
define any actual OFFQ flag yet.

Off-queue CPU number is now shifted by WORK_OFFQ_CPU_SHIFT, which adds
the number of bits used by OFFQ flags to WORK_STRUCT_FLAG_SHIFT, to
make room for OFFQ flags.

To avoid shift width warning with large WORK_OFFQ_FLAG_BITS, ulong
cast is added to WORK_STRUCT_NO_CPU and, just in case, BUILD_BUG_ON()
to check that there are enough bits to accomodate off-queue CPU number
is added.

This patch doesn't make any functional difference.

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2012-08-03 10:30:46 -07:00
parent bf4ede014e
commit b549007727
2 changed files with 16 additions and 6 deletions
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8
include/linux/workqueue.h
View file

@ -68,9 +68,15 @@ enum {
WORK_STRUCT_FLAG_BITS = WORK_STRUCT_COLOR_SHIFT +
WORK_STRUCT_COLOR_BITS,
/* data contains off-queue information when !WORK_STRUCT_CWQ */
WORK_OFFQ_FLAG_BASE = WORK_STRUCT_FLAG_BITS,
WORK_OFFQ_FLAG_BITS = 0,
WORK_OFFQ_CPU_SHIFT = WORK_OFFQ_FLAG_BASE + WORK_OFFQ_FLAG_BITS,
/* convenience constants */
WORK_STRUCT_FLAG_MASK = (1UL << WORK_STRUCT_FLAG_BITS) - 1,
WORK_STRUCT_WQ_DATA_MASK = ~WORK_STRUCT_FLAG_MASK,
WORK_STRUCT_NO_CPU = WORK_CPU_NONE << WORK_STRUCT_FLAG_BITS,
WORK_STRUCT_NO_CPU = (unsigned long)WORK_CPU_NONE << WORK_OFFQ_CPU_SHIFT,
/* bit mask for work_busy() return values */
WORK_BUSY_PENDING = 1 << 0,

14
kernel/workqueue.c
View file

@ -533,9 +533,9 @@ static int work_next_color(int color)
}
/*
* A work's data points to the cwq with WORK_STRUCT_CWQ set while the
* work is on queue. Once execution starts, WORK_STRUCT_CWQ is
* cleared and the work data contains the cpu number it was last on.
* While queued, %WORK_STRUCT_CWQ is set and non flag bits of a work's data
* contain the pointer to the queued cwq. Once execution starts, the flag
* is cleared and the high bits contain OFFQ flags and CPU number.
*
* set_work_cwq(), set_work_cpu_and_clear_pending() and clear_work_data()
* can be used to set the cwq, cpu or clear work->data. These functions
@ -565,7 +565,7 @@ static void set_work_cwq(struct work_struct *work,
static void set_work_cpu_and_clear_pending(struct work_struct *work,
unsigned int cpu)
{
set_work_data(work, cpu << WORK_STRUCT_FLAG_BITS, 0);
set_work_data(work, (unsigned long)cpu << WORK_OFFQ_CPU_SHIFT, 0);
}
static void clear_work_data(struct work_struct *work)
@ -592,7 +592,7 @@ static struct global_cwq *get_work_gcwq(struct work_struct *work)
return ((struct cpu_workqueue_struct *)
(data & WORK_STRUCT_WQ_DATA_MASK))->pool->gcwq;
cpu = data >> WORK_STRUCT_FLAG_BITS;
cpu = data >> WORK_OFFQ_CPU_SHIFT;
if (cpu == WORK_CPU_NONE)
return NULL;
@ -3724,6 +3724,10 @@ static int __init init_workqueues(void)
unsigned int cpu;
int i;
/* make sure we have enough bits for OFFQ CPU number */
BUILD_BUG_ON((1LU << (BITS_PER_LONG - WORK_OFFQ_CPU_SHIFT)) <
WORK_CPU_LAST);
cpu_notifier(workqueue_cpu_up_callback, CPU_PRI_WORKQUEUE_UP);
cpu_notifier(workqueue_cpu_down_callback, CPU_PRI_WORKQUEUE_DOWN);