Re: [RFC PATCH 1/1] block: introduce activity based ioprio

From: Zhaoyang Huang
Date: Thu Jan 18 2024 - 02:48:25 EST

On Wed, Jan 17, 2024 at 11:20 PM Jens Axboe <axboe@xxxxxxxxx> wrote:
>
> On 1/17/24 2:23 AM, zhaoyang.huang wrote:
> > [1]
> > ./fault_latency.bin 1 5 > /data/dd_costmem &
> > costmem -c0 -a2048000 -b128000 -o0 1>/dev/null &
> > costmem -c0 -a2048000 -b128000 -o0 1>/dev/null &
> > costmem -c0 -a2048000 -b128000 -o0 1>/dev/null &
> > costmem -c0 -a2048000 -b128000 -o0 1>/dev/null &
> > dd if=/dev/block/sda of=/data/ddtest bs=1024 count=2048000 &
> > dd if=/dev/block/sda of=/data/ddtest1 bs=1024 count=2048000 &
> > dd if=/dev/block/sda of=/data/ddtest2 bs=1024 count=2048000 &
> > dd if=/dev/block/sda of=/data/ddtest3 bs=1024 count=2048000
> >
> > [2]
> > mainline:
> > Summary for 5932.00(ms)
> > All Faults: 1398 235.67 counts/sec
> > Iowait: 553 93.22 counts/sec
> > All latency: 7432948 1253.03 us/ms
> > Iowait: 1321971 222.85 us/ms
> > Summary for 6706.00(ms)
> > All Faults: 1921 286.46 counts/sec
> > Iowait: 1273 189.83 counts/sec
> > All latency: 25890252 3860.76 us/ms
> > Iowait: 4468861 666.40 us/ms
> > Summary for 5838.00(ms)
> > All Faults: 1580 270.64 counts/sec
> > Iowait: 619 106.03 counts/sec
> > All latency: 6862215 1175.44 us/ms
> > Iowait: 1077616 184.59 us/ms
> > Summary for 5916.00(ms)
> > All Faults: 1195 201.99 counts/sec
> > Iowait: 494 83.50 counts/sec
> > All latency: 4555134 769.97 us/ms
> > Iowait: 902513 152.55 us/ms
> > Summary for 6229.00(ms)
> > All Faults: 1395 223.95 counts/sec
> > Iowait: 359 57.63 counts/sec
> > All latency: 6091882 977.99 us/ms
> > Iowait: 1251183 200.86 us/ms
> > Summary for 6059.00(ms)
> > All Faults: 1201 198.22 counts/sec
> > Iowait: 299 49.35 counts/sec
> > All latency: 5612143 926.25 us/ms
> > Iowait: 1155555 190.72 us/ms
> > Summary for 6005.00(ms)
> > All Faults: 847 141.05 counts/sec
> > Iowait: 320 53.29 counts/sec
> > All latency: 5852541 974.61 us/ms
> > Iowait: 433719 72.23 us/ms
> > Summary for 5895.00(ms)
> > All Faults: 1039 176.25 counts/sec
> > Iowait: 288 48.85 counts/sec
> > All latency: 4184680 709.87 us/ms
> > Iowait: 686266 116.41 us/ms
> > Summary for 6371.00(ms)
> > All Faults: 1176 184.59 counts/sec
> > Iowait: 269 42.22 counts/sec
> > All latency: 6282918 986.17 us/ms
> > Iowait: 1160952 182.22 us/ms
> > Summary for 6113.00(ms)
> > All Faults: 1322 216.26 counts/sec
> > Iowait: 281 45.97 counts/sec
> > All latency: 7208880 1179.27 us/ms
> > Iowait: 1336650 218.66 us/ms
> >
> > commit:
> > Summary for 7225.00(ms)
> > All Faults: 1384 191.56 counts/sec
> > Iowait: 285 39.45 counts/sec
> > All latency: 6593081 912.54 us/ms
> > Iowait: 934041 129.28 us/ms
> > Summary for 6567.00(ms)
> > All Faults: 1378 209.84 counts/sec
> > Iowait: 167 25.43 counts/sec
> > All latency: 3761554 572.80 us/ms
> > Iowait: 220621 33.60 us/ms
> > Summary for 6118.00(ms)
> > All Faults: 1304 213.14 counts/sec
> > Iowait: 268 43.81 counts/sec
> > All latency: 3835332 626.89 us/ms
> > Iowait: 413900 67.65 us/ms
> > Summary for 6155.00(ms)
> > All Faults: 1177 191.23 counts/sec
> > Iowait: 185 30.06 counts/sec
> > All latency: 4839084 786.20 us/ms
> > Iowait: 660002 107.23 us/ms
> > Summary for 6448.00(ms)
> > All Faults: 1283 198.98 counts/sec
> > Iowait: 353 54.75 counts/sec
> > All latency: 4798334 744.16 us/ms
> > Iowait: 1258045 195.11 us/ms
> > Summary for 6179.00(ms)
> > All Faults: 1285 207.96 counts/sec
> > Iowait: 137 22.17 counts/sec
> > All latency: 3668456 593.70 us/ms
> > Iowait: 419731 67.93 us/ms
> > Summary for 6165.00(ms)
> > All Faults: 1500 243.31 counts/sec
> > Iowait: 182 29.52 counts/sec
> > All latency: 3357435 544.60 us/ms
> > Iowait: 279828 45.39 us/ms
> > Summary for 6270.00(ms)
> > All Faults: 1507 240.35 counts/sec
> > Iowait: 361 57.58 counts/sec
> > All latency: 4428320 706.27 us/ms
> > Iowait: 741304 118.23 us/ms
> > Summary for 6597.00(ms)
> > All Faults: 1263 191.45 counts/sec
> > Iowait: 238 36.08 counts/sec
> > All latency: 5115168 775.38 us/ms
> > Iowait: 950482 144.08 us/ms
> > Summary for 6503.00(ms)
> > All Faults: 1456 223.90 counts/sec
> > Iowait: 402 61.82 counts/sec
> > All latency: 6782757 1043.02 us/ms
> > Iowait: 1483803 228.17 us/ms
>
> That's a lot of data, and I'm sure you did some analysis of this to
> conclude that the change makes a positive difference. It would be
> prudent to include such analysis, rather than just a raw dump of data.
> On top of that, you don't mention what you are testing on - what is sda?
Please find below for summary of the test result. The test case is
collecting io time of mmaped VA(from scheduler point of view) among
mix access of mmaped and vfs file data concurrently. sda is a raw disk
partition which is used for source data of command dd.
mainline commit
io cost 1379us 736us
>
> A few comments - regardless of whether or not this change makes
> functional sense.
The commit's basic idea is the request priority should be decided by
the pages it carry instead of(or together with) the launcher.
>
> > diff --git a/block/Kconfig.iosched b/block/Kconfig.iosched
> > index 27f11320b8d1..cd6fcfca7782 100644
> > --- a/block/Kconfig.iosched
> > +++ b/block/Kconfig.iosched
> > @@ -44,4 +44,11 @@ config BFQ_CGROUP_DEBUG
> > Enable some debugging help. Currently it exports additional stat
> > files in a cgroup which can be useful for debugging.
> >
> > +config ACTIVITY_BASED_IOPRIO
> > + bool "Enable folio activity based ioprio on deadline"
> > + depends on LRU_GEN && MQ_IOSCHED_DEADLINE
> > + default n
> > + help
> > + This item enable the feature of adjust request's priority by
> > + calculating its folio's activity.
>
> Doesn't seem like this should be a config thing. In any case, 'default
> n' is the default, so you should kill that line.
ok
>
> > @@ -224,14 +225,42 @@ static void deadline_remove_request(struct request_queue *q,
> > q->last_merge = NULL;
> > }
> >
> > +static enum dd_prio dd_req_ioprio(struct request *rq)
> > +{
> > + enum dd_prio prio;
> > + const u8 ioprio_class = dd_rq_ioclass(rq);
> > +#ifdef CONFIG_ACTIVITY_BASED_IOPRIO
> > + struct bio *bio;
> > + struct bio_vec bv;
> > + struct bvec_iter iter;
> > + struct page *page;
> > + int gen = 0;
> > + int cnt = 0;
> > +
> > + if (req_op(rq) == REQ_OP_READ) {
> > + __rq_for_each_bio(bio, rq) {
> > + bio_for_each_bvec(bv, bio, iter) {
> > + page = bv.bv_page;
> > + gen += PageWorkingset(page) ? 1 : 0;
> > + cnt++;
> > + }
> > + }
> > + prio = (gen >= cnt / 2) ? ioprio_class_to_prio[IOPRIO_CLASS_RT] :
> > + ioprio_class_to_prio[ioprio_class];
> > + } else
> > + prio = ioprio_class_to_prio[ioprio_class];
> > +#else
> > + prio = ioprio_class_to_prio[ioprio_class];
> > +#endif
> > + return prio;
> > +}
>
> This is pretty awful imho, you're iterating the pages which isn't
> exactly cheap. There's also a ternary operator (get rid of it), and
> magic cnt / 2 which isn't even explained.
ok. The iterating is on purpose here to not enlarge the bio and
request structure. The magic number would be replaced by an more
sensible criteria like MULTI_GEN's thrashing tier things.
>
> This would make much more sense to do when the page is added to the bio,
> rather than try and fix up the prio after the fact.
>
> > static void dd_request_merged(struct request_queue *q, struct request *req,
> > enum elv_merge type)
> > {
> > struct deadline_data *dd = q->elevator->elevator_data;
> > - const u8 ioprio_class = dd_rq_ioclass(req);
> > - const enum dd_prio prio = ioprio_class_to_prio[ioprio_class];
> > + const enum dd_prio prio = dd_req_ioprio(req);
> > struct dd_per_prio *per_prio = &dd->per_prio[prio];
> > -
> > /*
> > * if the merge was a front merge, we need to reposition request
> > */
> > @@ -248,8 +277,7 @@ static void dd_merged_requests(struct request_queue *q, struct request *req,
> > struct request *next)
> > {
> > struct deadline_data *dd = q->elevator->elevator_data;
> > - const u8 ioprio_class = dd_rq_ioclass(next);
> > - const enum dd_prio prio = ioprio_class_to_prio[ioprio_class];
> > + const enum dd_prio prio = dd_req_ioprio(next);
> >
> > lockdep_assert_held(&dd->lock);
>
> What are these changes?
That is for code's integrity of getting the request's prio for either
this feature enabled or not.
>
> > @@ -745,10 +773,30 @@ static int dd_request_merge(struct request_queue *q, struct request **rq,
> > {
> > struct deadline_data *dd = q->elevator->elevator_data;
> > const u8 ioprio_class = IOPRIO_PRIO_CLASS(bio->bi_ioprio);
> > - const enum dd_prio prio = ioprio_class_to_prio[ioprio_class];
> > - struct dd_per_prio *per_prio = &dd->per_prio[prio];
> > + struct dd_per_prio *per_prio;
> > sector_t sector = bio_end_sector(bio);
> > struct request *__rq;
> > +#ifdef CONFIG_ACTIVITY_BASED_IOPRIO
> > + enum dd_prio prio;
> > + struct bio_vec bv;
> > + struct bvec_iter iter;
> > + struct page *page;
> > + int gen = 0;
> > + int cnt = 0;
> > +
> > + if (bio_op(bio) == REQ_OP_READ) {
> > + bio_for_each_bvec(bv, bio, iter) {
> > + page = bv.bv_page;
> > + gen += PageWorkingset(page) ? 1 : 0;
> > + cnt++;
> > + }
> > + }
> > + prio = (gen >= cnt / 2) ? ioprio_class_to_prio[IOPRIO_CLASS_RT] :
> > + ioprio_class_to_prio[ioprio_class];
> > +#else
> > + const enum dd_prio prio = ioprio_class_to_prio[ioprio_class];
> > +#endif
> > + per_prio = &dd->per_prio[prio];
>
> And here you duplicate the entire thing from above again?
could be solved by updating the dd_req_ioprio
>
> > @@ -798,10 +846,8 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
> > struct request_queue *q = hctx->queue;
> > struct deadline_data *dd = q->elevator->elevator_data;
> > const enum dd_data_dir data_dir = rq_data_dir(rq);
> > - u16 ioprio = req_get_ioprio(rq);
> > - u8 ioprio_class = IOPRIO_PRIO_CLASS(ioprio);
> > struct dd_per_prio *per_prio;
> > - enum dd_prio prio;
> > + enum dd_prio prio = dd_req_ioprio(rq);
> >
> > lockdep_assert_held(&dd->lock);
> >
> > @@ -811,7 +857,6 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
> > */
> > blk_req_zone_write_unlock(rq);
> >
> > - prio = ioprio_class_to_prio[ioprio_class];
> > per_prio = &dd->per_prio[prio];
> > if (!rq->elv.priv[0]) {
> > per_prio->stats.inserted++;
> > @@ -920,8 +965,7 @@ static void dd_finish_request(struct request *rq)
> > {
> > struct request_queue *q = rq->q;
> > struct deadline_data *dd = q->elevator->elevator_data;
> > - const u8 ioprio_class = dd_rq_ioclass(rq);
> > - const enum dd_prio prio = ioprio_class_to_prio[ioprio_class];
> > + const enum dd_prio prio = dd_req_ioprio(rq);
> > struct dd_per_prio *per_prio = &dd->per_prio[prio];
>
> And again these changes?
>
> --
> Jens Axboe
>