Hi Qu,
On Fri, Feb 28, 2014 at 4:46 AM, Qu Wenruo <quwen...@cn.fujitsu.com> wrote:
> The original btrfs_workers has thresholding functions to dynamically
> create or destroy kthreads.
>
> Though there is no such function in kernel workqueue because the worker
> is not created manually, we can still use the workqueue_set_max_active
> to simulated the behavior, mainly to achieve a better HDD performance by
> setting a high threshold on submit_workers.
> (Sadly, no resource can be saved)
>
> So in this patch, extra workqueue pending counters are introduced to
> dynamically change the max active of each btrfs_workqueue_struct, hoping
> to restore the behavior of the original thresholding function.
>
> Also, workqueue_set_max_active use a mutex to protect workqueue_struct,
> which is not meant to be called too frequently, so a new interval
> mechanism is applied, that will only call workqueue_set_max_active after
> a count of work is queued. Hoping to balance both the random and
> sequence performance on HDD.
>
> Signed-off-by: Qu Wenruo <quwen...@cn.fujitsu.com>
> Tested-by: David Sterba <dste...@suse.cz>
> ---
> Changelog:
> v2->v3:
> - Add thresholding mechanism to simulate the old thresholding mechanism.
> - Will not enable thresholding when thresh is set to small value.
> v3->v4:
> None
> v4->v5:
> None
> ---
> fs/btrfs/async-thread.c | 107
> ++++++++++++++++++++++++++++++++++++++++++++----
> fs/btrfs/async-thread.h | 3 +-
> 2 files changed, 101 insertions(+), 9 deletions(-)
>
> diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c
> index 193c849..977bce2 100644
> --- a/fs/btrfs/async-thread.c
> +++ b/fs/btrfs/async-thread.c
> @@ -30,6 +30,9 @@
> #define WORK_ORDER_DONE_BIT 2
> #define WORK_HIGH_PRIO_BIT 3
>
> +#define NO_THRESHOLD (-1)
> +#define DFT_THRESHOLD (32)
> +
> /*
> * container for the kthread task pointer and the list of pending work
> * One of these is allocated per thread.
> @@ -737,6 +740,14 @@ struct __btrfs_workqueue_struct {
>
> /* Spinlock for ordered_list */
> spinlock_t list_lock;
> +
> + /* Thresholding related variants */
> + atomic_t pending;
> + int max_active;
> + int current_max;
> + int thresh;
> + unsigned int count;
> + spinlock_t thres_lock;
> };
>
> struct btrfs_workqueue_struct {
> @@ -745,19 +756,34 @@ struct btrfs_workqueue_struct {
> };
>
> static inline struct __btrfs_workqueue_struct
> -*__btrfs_alloc_workqueue(char *name, int flags, int max_active)
> +*__btrfs_alloc_workqueue(char *name, int flags, int max_active, int thresh)
> {
> struct __btrfs_workqueue_struct *ret = kzalloc(sizeof(*ret),
> GFP_NOFS);
>
> if (unlikely(!ret))
> return NULL;
>
> + ret->max_active = max_active;
> + atomic_set(&ret->pending, 0);
> + if (thresh == 0)
> + thresh = DFT_THRESHOLD;
> + /* For low threshold, disabling threshold is a better choice */
> + if (thresh < DFT_THRESHOLD) {
> + ret->current_max = max_active;
> + ret->thresh = NO_THRESHOLD;
> + } else {
> + ret->current_max = 1;
> + ret->thresh = thresh;
> + }
> +
> if (flags & WQ_HIGHPRI)
> ret->normal_wq = alloc_workqueue("%s-%s-high", flags,
> - max_active, "btrfs", name);
> + ret->max_active,
> + "btrfs", name);
> else
> ret->normal_wq = alloc_workqueue("%s-%s", flags,
> - max_active, "btrfs", name);
> + ret->max_active, "btrfs",
> + name);
Shouldn't we use ret->current_max instead of ret->max_active (in both calls)?
According to the rest of the code, "max_active" is the absolute
maximum beyond which the "normal_wq" cannot go (you use clamp_value to
ensure that). And "current_max" is the current value of "max_active"
of the "normal_wq". But here, you set the "normal_wq" to "max_active"
immediately. Is this intentional?
> if (unlikely(!ret->normal_wq)) {
> kfree(ret);
> return NULL;
> @@ -765,6 +791,7 @@ static inline struct __btrfs_workqueue_struct
>
> INIT_LIST_HEAD(&ret->ordered_list);
> spin_lock_init(&ret->list_lock);
> + spin_lock_init(&ret->thres_lock);
> return ret;
> }
>
> @@ -773,7 +800,8 @@ __btrfs_destroy_workqueue(struct __btrfs_workqueue_struct
> *wq);
>
> struct btrfs_workqueue_struct *btrfs_alloc_workqueue(char *name,
> int flags,
> - int max_active)
> + int max_active,
> + int thresh)
> {
> struct btrfs_workqueue_struct *ret = kzalloc(sizeof(*ret), GFP_NOFS);
>
> @@ -781,14 +809,15 @@ struct btrfs_workqueue_struct
> *btrfs_alloc_workqueue(char *name,
> return NULL;
>
> ret->normal = __btrfs_alloc_workqueue(name, flags & ~WQ_HIGHPRI,
> - max_active);
> + max_active, thresh);
> if (unlikely(!ret->normal)) {
> kfree(ret);
> return NULL;
> }
>
> if (flags & WQ_HIGHPRI) {
> - ret->high = __btrfs_alloc_workqueue(name, flags, max_active);
> + ret->high = __btrfs_alloc_workqueue(name, flags, max_active,
> + thresh);
> if (unlikely(!ret->high)) {
> __btrfs_destroy_workqueue(ret->normal);
> kfree(ret);
> @@ -798,6 +827,66 @@ struct btrfs_workqueue_struct
> *btrfs_alloc_workqueue(char *name,
> return ret;
> }
>
> +/*
> + * Hook for threshold which will be called in btrfs_queue_work.
> + * This hook WILL be called in IRQ handler context,
> + * so workqueue_set_max_active MUST NOT be called in this hook
> + */
> +static inline void thresh_queue_hook(struct __btrfs_workqueue_struct *wq)
> +{
> + if (wq->thresh == NO_THRESHOLD)
> + return;
> + atomic_inc(&wq->pending);
> +}
> +
> +/*
> + * Hook for threshold which will be called before executing the work,
> + * This hook is called in kthread content.
> + * So workqueue_set_max_active is called here.
> + */
> +static inline void thresh_exec_hook(struct __btrfs_workqueue_struct *wq)
> +{
> + int new_max_active;
> + long pending;
> + int need_change = 0;
> +
> + if (wq->thresh == NO_THRESHOLD)
> + return;
> +
> + atomic_dec(&wq->pending);
> + spin_lock(&wq->thres_lock);
> + /*
> + * Use wq->count to limit the calling frequency of
> + * workqueue_set_max_active.
> + */
> + wq->count++;
> + wq->count %= (wq->thresh / 4);
> + if (!wq->count)
> + goto out;
> + new_max_active = wq->current_max;
> +
> + /*
> + * pending may be changed later, but it's OK since we really
> + * don't need it so accurate to calculate new_max_active.
> + */
> + pending = atomic_read(&wq->pending);
> + if (pending > wq->thresh)
> + new_max_active++;
> + if (pending < wq->thresh / 2)
> + new_max_active--;
> + new_max_active = clamp_val(new_max_active, 1, wq->max_active);
> + if (new_max_active != wq->current_max) {
> + need_change = 1;
> + wq->current_max = new_max_active;
> + }
> +out:
> + spin_unlock(&wq->thres_lock);
> +
> + if (need_change) {
> + workqueue_set_max_active(wq->normal_wq, wq->current_max);
Here you se the "normal_wq" max_active to "current_max", but not when
the normal workqueue has been created initially.
> + }
> +}
> +
> static void run_ordered_work(struct __btrfs_workqueue_struct *wq)
> {
> struct list_head *list = &wq->ordered_list;
> @@ -858,6 +947,7 @@ static void normal_work_helper(struct work_struct *arg)
> need_order = 1;
> wq = work->wq;
>
> + thresh_exec_hook(wq);
> work->func(work);
> if (need_order) {
> set_bit(WORK_DONE_BIT, &work->flags);
> @@ -884,6 +974,7 @@ static inline void __btrfs_queue_work(struct
> __btrfs_workqueue_struct *wq,
> unsigned long flags;
>
> work->wq = wq;
> + thresh_queue_hook(wq);
> if (work->ordered_func) {
> spin_lock_irqsave(&wq->list_lock, flags);
> list_add_tail(&work->ordered_list, &wq->ordered_list);
> @@ -922,9 +1013,9 @@ void btrfs_destroy_workqueue(struct
> btrfs_workqueue_struct *wq)
>
> void btrfs_workqueue_set_max(struct btrfs_workqueue_struct *wq, int max)
> {
> - workqueue_set_max_active(wq->normal->normal_wq, max);
> + wq->normal->max_active = max;
> if (wq->high)
> - workqueue_set_max_active(wq->high->normal_wq, max);
> + wq->high->max_active = max;
> }
>
> void btrfs_set_work_high_priority(struct btrfs_work_struct *work)
> diff --git a/fs/btrfs/async-thread.h b/fs/btrfs/async-thread.h
> index fce623c..3129d8a 100644
> --- a/fs/btrfs/async-thread.h
> +++ b/fs/btrfs/async-thread.h
> @@ -138,7 +138,8 @@ struct btrfs_work_struct {
>
> struct btrfs_workqueue_struct *btrfs_alloc_workqueue(char *name,
> int flags,
> - int max_active);
> + int max_active,
> + int thresh);
> void btrfs_init_work(struct btrfs_work_struct *work,
> void (*func)(struct btrfs_work_struct *),
> void (*ordered_func)(struct btrfs_work_struct *),
> --
> 1.9.0
>
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Thanks,
Alex.
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