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SubjectRe: [PATCH V2 2/2] block: kyber: make kyber more friendly with merging
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Hi Omar

Thanks for your kindly and detailed comment.
That's really appreciated. :)

On 05/30/2018 02:55 AM, Omar Sandoval wrote:
> On Wed, May 23, 2018 at 02:33:22PM +0800, Jianchao Wang wrote:
>> Currently, kyber is very unfriendly with merging. kyber depends
>> on ctx rq_list to do merging, however, most of time, it will not
>> leave any requests in ctx rq_list. This is because even if tokens
>> of one domain is used up, kyber will try to dispatch requests
>> from other domain and flush the rq_list there.
>>
>> To improve this, we setup kyber_ctx_queue (kcq) which is similar
>> with ctx, but it has rq_lists for different domain and build same
>> mapping between kcq and khd as the ctx & hctx. Then we could merge,
>> insert and dispatch for different domains separately. At the same
>> time, only flush the rq_list of kcq when get domain token successfully.
>> Then if one domain token is used up, the requests could be left in
>> the rq_list of that domain and maybe merged with following io.
>>
>> Following is my test result on machine with 8 cores and NVMe card
>> INTEL SSDPEKKR128G7
>>
>> fio size=256m ioengine=libaio iodepth=64 direct=1 numjobs=8
>> seq/random
>> +------+---------------------------------------------------------------+
>> |patch?| bw(MB/s) | iops | slat(usec) | clat(usec) | merge |
>> +----------------------------------------------------------------------+
>> | w/o | 606/612 | 151k/153k | 6.89/7.03 | 3349.21/3305.40 | 0/0 |
>> +----------------------------------------------------------------------+
>> | w/ | 1083/616 | 277k/154k | 4.93/6.95 | 1830.62/3279.95 | 223k/3k |
>> +----------------------------------------------------------------------+
>> When set numjobs to 16, the bw and iops could reach 1662MB/s and 425k
>> on my platform.
>>
>> Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
>> Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
>
> Thanks, the per-hctx kqcs make much more sense. This is pretty cool! A
> few nitpicks below.
>
>> ---
>> block/kyber-iosched.c | 197 +++++++++++++++++++++++++++++++++++++++++---------
>> 1 file changed, 162 insertions(+), 35 deletions(-)
>>
>> diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
>> index 0d6d25e3..7ca1364 100644
>> --- a/block/kyber-iosched.c
>> +++ b/block/kyber-iosched.c
>> @@ -72,6 +72,15 @@ static const unsigned int kyber_batch_size[] = {
>> [KYBER_OTHER] = 8,
>> };
>>
>> +struct kyber_ctx_queue {
>
> I'm not crazy about this name, but I can't really think of anything
> better, so this will have to do.

Yes, me too

>
>> + /*
>> + * Copied from blk_mq_ctx->index_hw
>> + */
>> + unsigned int index;
>
> We can just calculate this as kcq - khd->kcqs in the one place we use
> it.

except for this, we could also use req->mq_ctx->index_hw which has been
used to get kcq.

>
>> + spinlock_t lock;
>> + struct list_head rq_list[KYBER_NUM_DOMAINS];
>> +} ____cacheline_aligned_in_smp;
>> +
>> struct kyber_queue_data {
>> struct request_queue *q;
>>
>> @@ -99,6 +108,8 @@ struct kyber_hctx_data {
>> struct list_head rqs[KYBER_NUM_DOMAINS];
>> unsigned int cur_domain;
>> unsigned int batching;
>> + struct kyber_ctx_queue *kcqs;
>> + struct sbitmap kcq_map[KYBER_NUM_DOMAINS];
>> wait_queue_entry_t domain_wait[KYBER_NUM_DOMAINS];
>> struct sbq_wait_state *domain_ws[KYBER_NUM_DOMAINS];
>> atomic_t wait_index[KYBER_NUM_DOMAINS];
>> @@ -107,10 +118,8 @@ struct kyber_hctx_data {
>> static int kyber_domain_wake(wait_queue_entry_t *wait, unsigned mode, int flags,
>> void *key);
>>
>> -static int rq_sched_domain(const struct request *rq)
>> +static int kyber_sched_domain(unsigned int op)
>
> Please make this return an unsigned int since that's what we use for
> sched_domain everywhere except the stats bucket function.

Yes, done

>
>> {
>> - unsigned int op = rq->cmd_flags;
>> -
>> if ((op & REQ_OP_MASK) == REQ_OP_READ)
>> return KYBER_READ;
>> else if ((op & REQ_OP_MASK) == REQ_OP_WRITE && op_is_sync(op))
>> @@ -284,6 +293,11 @@ static unsigned int kyber_sched_tags_shift(struct kyber_queue_data *kqd)
>> return kqd->q->queue_hw_ctx[0]->sched_tags->bitmap_tags.sb.shift;
>> }
>>
>> +static int kyber_bucket_fn(const struct request *rq)
>> +{
>> + return kyber_sched_domain(rq->cmd_flags);
>> +}
>> +
>> static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
>> {
>> struct kyber_queue_data *kqd;
>> @@ -297,11 +311,10 @@ static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
>> goto err;
>> kqd->q = q;
>>
>> - kqd->cb = blk_stat_alloc_callback(kyber_stat_timer_fn, rq_sched_domain,
>> + kqd->cb = blk_stat_alloc_callback(kyber_stat_timer_fn, kyber_bucket_fn,
>> KYBER_NUM_DOMAINS, kqd);
>> if (!kqd->cb)
>> goto err_kqd;
>> -
> > Unrelated whitespace change.

Done

>
>> /*
>> * The maximum number of tokens for any scheduling domain is at least
>> * the queue depth of a single hardware queue. If the hardware doesn't
>> @@ -376,15 +389,45 @@ static void kyber_exit_sched(struct elevator_queue *e)
>> kfree(kqd);
>> }
>>
>> +static void kyber_ctx_queue_init(struct kyber_ctx_queue *kcq)
>> +{
>> + unsigned int i;
>> +
>> + spin_lock_init(&kcq->lock);
>> + for (i = 0; i < KYBER_NUM_DOMAINS; i++)
>> + INIT_LIST_HEAD(&kcq->rq_list[i]);
>> +}
>> +
>> static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
>> {
>> struct kyber_hctx_data *khd;
>> - int i;
>> + int i, sd;
>>
>> khd = kmalloc_node(sizeof(*khd), GFP_KERNEL, hctx->numa_node);
>> if (!khd)
>> return -ENOMEM;
>>
>> + khd->kcqs = kmalloc_array_node(hctx->nr_ctx,
>> + sizeof(struct kyber_ctx_queue),
>> + GFP_KERNEL, hctx->numa_node);
>
> Argument whitespace alignment is still wrong here. I guess you have to
> pass --strict to checkpatch.pl to get it to warn about that. Usually I
> wouldn't be nitpicky about this but I made sure to keep this file nice
> and neat, and we need a v3 anyways :)

Yes, absolutely.

>
>> + if (!khd->kcqs)
>> + goto err_khd;
>> + /*
>> + * clone the mapping between hctx and ctx to khd and kcq
>> + */
>> + for (i = 0; i < hctx->nr_ctx; i++) {
>> + kyber_ctx_queue_init(&khd->kcqs[i]);
>> + khd->kcqs[i].index = i;
>> + }
>> +
>> + sd = 0;
>> + for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
>> + if (sbitmap_init_node(&khd->kcq_map[i], hctx->nr_ctx,
>> + ilog2(8), GFP_KERNEL, hctx->numa_node))
>
> Whitespace again.
>
>> + goto err_kcq_map;
>
> In this error case, I'd prefer if we did something similar to
> kyber_queue_data_alloc() instead of having this obscurely-named sd
> variable:
>
> while (--i >= 0)
> sbitmap_free(&khd->kcq_map[i]);
> goto err_kcqs;
>
> Where err_kcqs is just the kfree(khd->kcqs).

Yes, done

>
>> + sd++;
>> + }
>> +
>> spin_lock_init(&khd->lock);
>>
>> for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
>> @@ -402,10 +445,24 @@ static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
>> hctx->sched_data = khd;
>>
>> return 0;
>> +
>> +err_kcq_map:
>> + for (i = 0; i < sd; i++)
>> + sbitmap_free(&khd->kcq_map[i]);
>> + kfree(khd->kcqs);
>> +err_khd:
>> + kfree(khd);
>> + return -ENOMEM;
>> }
>>
>> static void kyber_exit_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
>> {
>> + struct kyber_hctx_data *khd = hctx->sched_data;
>> + int i;
>> +
>> + for (i = 0; i < KYBER_NUM_DOMAINS; i++)
>> + sbitmap_free(&khd->kcq_map[i]);
>> + kfree(khd->kcqs);
>> kfree(hctx->sched_data);
>> }
>>
>> @@ -427,7 +484,7 @@ static void rq_clear_domain_token(struct kyber_queue_data *kqd,
>>
>> nr = rq_get_domain_token(rq);
>> if (nr != -1) {
>> - sched_domain = rq_sched_domain(rq);
>> + sched_domain = kyber_sched_domain(rq->cmd_flags);
>> sbitmap_queue_clear(&kqd->domain_tokens[sched_domain], nr,
>> rq->mq_ctx->cpu);
>> }
>> @@ -446,11 +503,51 @@ static void kyber_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
>> }
>> }
>>
>> +static bool kyber_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio)
>> +{
>> + struct kyber_hctx_data *khd = hctx->sched_data;
>> + struct blk_mq_ctx *ctx = blk_mq_get_ctx(hctx->queue);
>> + struct kyber_ctx_queue *kcq = &khd->kcqs[ctx->index_hw];
>> + struct list_head *rq_list = &kcq->rq_list[kyber_sched_domain(bio->bi_opf)];
>> + bool merged;
>> +
>> + spin_lock(&kcq->lock);
>> + merged = blk_mq_bio_list_merge(hctx->queue, rq_list, bio);
>> + spin_unlock(&kcq->lock);
>> + blk_mq_put_ctx(ctx);
>> +
>> + return merged;
>> +}
>> +
>> static void kyber_prepare_request(struct request *rq, struct bio *bio)
>> {
>> rq_set_domain_token(rq, -1);
>> }
>>
>> +static void kyber_insert_requests(struct blk_mq_hw_ctx *hctx,
>> + struct list_head *rq_list, bool at_head)
>
> Whitespace.
>
>> +{
>> + struct kyber_hctx_data *khd = hctx->sched_data;
>> + struct kyber_ctx_queue *kcq;
>> + struct request *rq, *next;
>> + struct list_head *head;
>> + unsigned int sched_domain;
>> +
>> + list_for_each_entry_safe(rq, next, rq_list, queuelist) {
>
> Please declare the variables which are local to the loop iteration
> inside of the loop body. I.e.,
>
> unsigned int sched_domain;
> struct kyber_ctx_queue *kcq;
> struct list_head *head;
>

Done

>> + sched_domain = kyber_sched_domain(rq->cmd_flags);
>> + kcq = &khd->kcqs[rq->mq_ctx->index_hw];
>> + head = &kcq->rq_list[sched_domain];
>> + spin_lock(&kcq->lock);
>> + if (at_head)
>> + list_move(&rq->queuelist, head);
>> + else
>> + list_move_tail(&rq->queuelist, head);
>> + sbitmap_set_bit(&khd->kcq_map[sched_domain], kcq->index);
>> + blk_mq_sched_request_inserted(rq);
>> + spin_unlock(&kcq->lock);
>> + }
>> +}
>> +
>> static void kyber_finish_request(struct request *rq)
>> {
>> struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;
>> @@ -469,7 +566,7 @@ static void kyber_completed_request(struct request *rq)
>> * Check if this request met our latency goal. If not, quickly gather
>> * some statistics and start throttling.
>> */
>> - sched_domain = rq_sched_domain(rq);
>> + sched_domain = kyber_sched_domain(rq->cmd_flags);
>> switch (sched_domain) {
>> case KYBER_READ:
>> target = kqd->read_lat_nsec;
>> @@ -495,19 +592,36 @@ static void kyber_completed_request(struct request *rq)
>> blk_stat_activate_msecs(kqd->cb, 10);
>> }
>>
>> -static void kyber_flush_busy_ctxs(struct kyber_hctx_data *khd,
>> - struct blk_mq_hw_ctx *hctx)
>> +struct flush_kcq_data {
>> + struct kyber_hctx_data *khd;
>> + unsigned int sched_domain;
>> + struct list_head *list;
>> +};
>> +
>> +static bool flush_busy_kcq(struct sbitmap *sb, unsigned int bitnr, void *data)
>> {
>> - LIST_HEAD(rq_list);
>> - struct request *rq, *next;
>> + struct flush_kcq_data *flush_data = data;
>> + struct kyber_ctx_queue *kcq = &flush_data->khd->kcqs[bitnr];
>>
>> - blk_mq_flush_busy_ctxs(hctx, &rq_list);
>> - list_for_each_entry_safe(rq, next, &rq_list, queuelist) {
>> - unsigned int sched_domain;
>> + spin_lock(&kcq->lock);
>> + list_splice_tail_init(&kcq->rq_list[flush_data->sched_domain],
>> + flush_data->list);
>> + sbitmap_clear_bit(sb, bitnr);
>> + spin_unlock(&kcq->lock);
>>
>> - sched_domain = rq_sched_domain(rq);
>> - list_move_tail(&rq->queuelist, &khd->rqs[sched_domain]);
>> - }
>> + return true;
>> +}
>> +
>> +static void kyber_flush_busy_kcqs(struct kyber_hctx_data *khd,
>> + unsigned int sched_domain, struct list_head *list)
>> +{
>> + struct flush_kcq_data data = {
>> + .khd = khd,
>> + .sched_domain = sched_domain,
>> + .list = list,
>> + };
>> +
>> + sbitmap_for_each_set(&khd->kcq_map[sched_domain], flush_busy_kcq, &data);
>> }
>>
>> static int kyber_domain_wake(wait_queue_entry_t *wait, unsigned mode, int flags,
>> @@ -570,26 +684,19 @@ static int kyber_get_domain_token(struct kyber_queue_data *kqd,
>> static struct request *
>> kyber_dispatch_cur_domain(struct kyber_queue_data *kqd,
>> struct kyber_hctx_data *khd,
>> - struct blk_mq_hw_ctx *hctx,
>> - bool *flushed)
>> + struct blk_mq_hw_ctx *hctx)
>> {
>> struct list_head *rqs;
>> struct request *rq;
>> int nr;
>>
>> rqs = &khd->rqs[khd->cur_domain];
>> - rq = list_first_entry_or_null(rqs, struct request, queuelist);
>>
>> /*
>> - * If there wasn't already a pending request and we haven't flushed the
>> - * software queues yet, flush the software queues and check again.
>> + * If we do have cur_domain rqs on khd or kcq list, then try to require
>> + * the token
>> */
>> - if (!rq && !*flushed) {
>> - kyber_flush_busy_ctxs(khd, hctx);
>> - *flushed = true;
>> - rq = list_first_entry_or_null(rqs, struct request, queuelist);
>> - }
>> -
>> + rq = list_first_entry_or_null(rqs, struct request, queuelist);
>> if (rq) {
>> nr = kyber_get_domain_token(kqd, khd, hctx);
>> if (nr >= 0) {
>> @@ -598,8 +705,25 @@ kyber_dispatch_cur_domain(struct kyber_queue_data *kqd,
>> list_del_init(&rq->queuelist);
>> return rq;
>> }
>> + } else if (sbitmap_any_bit_set(&khd->kcq_map[khd->cur_domain])) {
>> + nr = kyber_get_domain_token(kqd, khd, hctx);
>> + if (nr >= 0) {
>> + kyber_flush_busy_kcqs(khd, khd->cur_domain, rqs);
>> + rq = list_first_entry_or_null(rqs, struct request, queuelist);
>
> This should just be list_first_entry() if we're so sure that we will
> always get a request.
>
>> + /*
>> + * khd->lock and kcq->lock will ensure that, if kcq_map[cur_domain]
>> + * is set, we must be able to get requests from the kcq
>> + */
>> + khd->batching++;
>> + rq_set_domain_token(rq, nr);
>> + list_del_init(&rq->queuelist);
>> + return rq;
>> + }
>> + /*
>> + * if not get domain token, the rqs could be left on kcqs to merged
>> + * with following ios.
>> + */
>> }
>> -
>> /* There were either no pending requests or no tokens. */
>> return NULL;
>> }
>
> Clever logic in this function :) I think it needs a more complete
> explanation rather than the little pieces sprinkled about, how about
> this (applied on top of your patch):

Yes, this is better, applied following changes. :)

>
> diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
> index f60bb4ce1fe6..f4f17527b7be 100644
> --- a/block/kyber-iosched.c
> +++ b/block/kyber-iosched.c
> @@ -696,8 +696,12 @@ kyber_dispatch_cur_domain(struct kyber_queue_data *kqd,
> rqs = &khd->rqs[khd->cur_domain];
>
> /*
> - * If we do have cur_domain rqs on khd or kcq list, then try to require
> - * the token
> + * If we already have a flushed request, then we just need to get a
> + * token for it. Otherwise, if there are pending requests in the kcqs,
> + * flush the kcqs, but only if we can get a token. If not, we should
> + * leave the requests in the kcqs so that they can be merged. Note that
> + * khd->lock serializes the flushes, so if we observed any bit set in
> + * the kcq_map, we will always get a request.
> */
> rq = list_first_entry_or_null(rqs, struct request, queuelist);
> if (rq) {
> @@ -712,20 +716,12 @@ kyber_dispatch_cur_domain(struct kyber_queue_data *kqd,
> nr = kyber_get_domain_token(kqd, khd, hctx);
> if (nr >= 0) {
> kyber_flush_busy_kcqs(khd, khd->cur_domain, rqs);
> - rq = list_first_entry_or_null(rqs, struct request, queuelist);
> - /*
> - * khd->lock and kcq->lock will ensure that, if kcq_map[cur_domain]
> - * is set, we must be able to get requests from the kcq
> - */
> + rq = list_first_entry(rqs, struct request, queuelist);
> khd->batching++;
> rq_set_domain_token(rq, nr);
> list_del_init(&rq->queuelist);
> return rq;
> }
> - /*
> - * if not get domain token, the rqs could be left on kcqs to merged
> - * with following ios.
> - */
> }
> /* There were either no pending requests or no tokens. */
> return NULL;
> >> @@ -608,7 +732,6 @@ static struct request *kyber_dispatch_request(struct blk_mq_hw_ctx *hctx)
>> {
>> struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
>> struct kyber_hctx_data *khd = hctx->sched_data;
>> - bool flushed = false;
>> struct request *rq;
>> int i;
>>
>> @@ -619,7 +742,7 @@ static struct request *kyber_dispatch_request(struct blk_mq_hw_ctx *hctx)
>> * from the batch.
>> */
>> if (khd->batching < kyber_batch_size[khd->cur_domain]) {
>> - rq = kyber_dispatch_cur_domain(kqd, khd, hctx, &flushed);
>> + rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
>> if (rq)
>> goto out;
>> }
>> @@ -640,7 +763,7 @@ static struct request *kyber_dispatch_request(struct blk_mq_hw_ctx *hctx)
>> else
>> khd->cur_domain++;
>>
>> - rq = kyber_dispatch_cur_domain(kqd, khd, hctx, &flushed);
>> + rq = kyber_dispatch_cur_domain(kqd, khd, hctx);
>> if (rq)
>> goto out;
>> }
>> @@ -657,10 +780,12 @@ static bool kyber_has_work(struct blk_mq_hw_ctx *hctx)
>> int i;
>>
>> for (i = 0; i < KYBER_NUM_DOMAINS; i++) {
>> - if (!list_empty_careful(&khd->rqs[i]))
>> + if (!list_empty_careful(&khd->rqs[i]) ||
>> + sbitmap_any_bit_set(&khd->kcq_map[i]))
>
> Whitespace.

Have corrected all of the similar issues and passed the checkpatch.pl with --strict option.


Thanks again for your directive.
Jianchao

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