On Wed, May 07, 2025 at 03:49:41PM -0600, Uday Shankar wrote:
Add support in kublk for decoupled ublk_queues and ublk server threads. kublk now has two modes of operation:
- (preexisting mode) threads and queues are paired 1:1, and each thread services all the I/Os of one queue
- (new mode) thread and queue counts are independently configurable. threads service I/Os in a way that balances load across threads even if load is not balanced over queues. requires passing --round_robin
The new mode of operation is exercised by the new test_generic_08, which issues I/O against a single queue and verifies that each of the 8 ublk server threads handles exactly 1/8 of the total I/O count. Under the old mode of operation (i.e. without --round_robin), all I/O goes to one ublk server thread, and the test fails.
Signed-off-by: Uday Shankar ushankar@purestorage.com
tools/testing/selftests/ublk/Makefile | 1 + tools/testing/selftests/ublk/file_backed.c | 4 +- tools/testing/selftests/ublk/kublk.c | 96 ++++++++++++++++++---- tools/testing/selftests/ublk/kublk.h | 3 + tools/testing/selftests/ublk/null.c | 4 +- tools/testing/selftests/ublk/stripe.c | 4 +- tools/testing/selftests/ublk/test_generic_08.sh | 61 ++++++++++++++ .../selftests/ublk/trace/count_ios_per_tid.bt | 9 ++ 8 files changed, 160 insertions(+), 22 deletions(-)
diff --git a/tools/testing/selftests/ublk/Makefile b/tools/testing/selftests/ublk/Makefile index e2e7b1e52a06252f626df5606221d17e3106d0d3..f8579019f0d1f9185df098440611c3b75087073b 100644 --- a/tools/testing/selftests/ublk/Makefile +++ b/tools/testing/selftests/ublk/Makefile @@ -14,6 +14,7 @@ TEST_PROGS += test_generic_04.sh TEST_PROGS += test_generic_05.sh TEST_PROGS += test_generic_06.sh TEST_PROGS += test_generic_07.sh +TEST_PROGS += test_generic_08.sh TEST_PROGS += test_null_01.sh TEST_PROGS += test_null_02.sh diff --git a/tools/testing/selftests/ublk/file_backed.c b/tools/testing/selftests/ublk/file_backed.c index 563f11a21604bbf5b9531f69f806d09cdd785960..72e22f54f7fe60d26096ace4eb4001987fbe7b15 100644 --- a/tools/testing/selftests/ublk/file_backed.c +++ b/tools/testing/selftests/ublk/file_backed.c @@ -50,7 +50,7 @@ static int loop_queue_tgt_rw_io(struct ublk_queue *q, const struct ublksrv_io_de ublk_io_alloc_sqes(ublk_get_io(q, tag), sqe, 3);
- io_uring_prep_buf_register(sqe[0], 0, tag, q->q_id, tag);
- io_uring_prep_buf_register(sqe[0], 0, tag, q->q_id, ublk_get_io(q, tag)->buf_index);
->buf_index can be calculated runtime by adding helper of ublk_io_buf_idx(io), so the extra field can be avoided, CPU is fast than memory.
sqe[0]->flags |= IOSQE_CQE_SKIP_SUCCESS | IOSQE_IO_HARDLINK; sqe[0]->user_data = build_user_data(tag, ublk_cmd_op_nr(sqe[0]->cmd_op), 0, q->q_id, 1); @@ -62,7 +62,7 @@ static int loop_queue_tgt_rw_io(struct ublk_queue *q, const struct ublksrv_io_de sqe[1]->flags |= IOSQE_FIXED_FILE | IOSQE_IO_HARDLINK; sqe[1]->user_data = build_user_data(tag, ublk_op, 0, q->q_id, 1);
- io_uring_prep_buf_unregister(sqe[2], 0, tag, q->q_id, tag);
- io_uring_prep_buf_unregister(sqe[2], 0, tag, q->q_id, ublk_get_io(q, tag)->buf_index); sqe[2]->user_data = build_user_data(tag, ublk_cmd_op_nr(sqe[2]->cmd_op), 0, q->q_id, 1);
return 2; diff --git a/tools/testing/selftests/ublk/kublk.c b/tools/testing/selftests/ublk/kublk.c index 313689f94cd6361a9a0f4b9257085b2a62bc8b8c..27046bb6a13b99879ad164ff8eaabeba57e17387 100644 --- a/tools/testing/selftests/ublk/kublk.c +++ b/tools/testing/selftests/ublk/kublk.c @@ -478,8 +478,11 @@ static int ublk_thread_init(struct ublk_thread *t) } if (dev->dev_info.flags & UBLK_F_SUPPORT_ZERO_COPY) {
unsigned nr_ios = dev->dev_info.queue_depth * dev->dev_info.nr_hw_queues;unsigned max_nr_ios_per_thread = nr_ios / dev->nthreads;max_nr_ios_per_thread += !!(nr_ios % dev->nthreads);
&t->ring, dev->dev_info.queue_depth);
&t->ring, max_nr_ios_per_thread);@@ -612,18 +615,42 @@ int ublk_queue_io_cmd(struct ublk_io *io) static void ublk_submit_fetch_commands(struct ublk_thread *t) {
- /*
* Service exclusively the queue whose q_id matches our thread* index. This may change in the future.*/- struct ublk_queue *q = &t->dev->q[t->idx];
- struct ublk_queue *q; struct ublk_io *io;
- int i = 0;
- int i = 0, j = 0;
- for (i = 0; i < q->q_depth; i++) {
io = &q->ios[i];io->t = t;ublk_queue_io_cmd(io);
- if (t->dev->dev_info.flags & UBLK_F_RR_TAGS) {
You shouldn't depend on the generic feature of UBLK_F_RR_TAGS, which can be used for non-io-task too.
Here you need one helper of ublk_use_io_task(), or sort of flags.
/** Lexicographically order all the (qid,tag) pairs, with* qid taking priority, and give this thread every Nth* entry, where N is the total number of threads. The* offset is controlled by the thread index. This takes* load which may be imbalanced across the queues and* balances it across the threads.*/const struct ublksrv_ctrl_dev_info *dinfo = &t->dev->dev_info;int nr_ios = dinfo->nr_hw_queues * dinfo->queue_depth;for (i = t->idx; i < nr_ios; i += t->dev->nthreads, j++) {int q_id = i / dinfo->queue_depth;int tag = i % dinfo->queue_depth;
I understand UBLK_F_RR_TAGS means that IO with adjacent tag should be handled locally, but the above actually does the opposite, only IOs with non-adjacent tags are handled in same pthread, can you explain a bit why UBLK_F_RR_TAGS helps for this way?
q = &t->dev->q[q_id];io = &q->ios[tag];io->t = t;io->buf_index = j;ublk_queue_io_cmd(io);}- } else {
/** Service exclusively the queue whose q_id matches our* thread index.*/struct ublk_queue *q = &t->dev->q[t->idx];for (i = 0; i < q->q_depth; i++) {io = &q->ios[i];io->t = t;io->buf_index = i;ublk_queue_io_cmd(io);}} @@ -778,7 +805,8 @@ static void *ublk_io_handler_fn(void *data) return NULL; } /* IO perf is sensitive with queue pthread affinity on NUMA machine*/
- ublk_thread_set_sched_affinity(t, info->affinity);
- if (info->affinity)
ublk_thread_set_sched_affinity(t, info->affinity);ublk_dbg(UBLK_DBG_THREAD, "tid %d: ublk dev %d thread %u started\n", @@ -844,7 +872,7 @@ static int ublk_start_daemon(const struct dev_ctx *ctx, struct ublk_dev *dev) ublk_dbg(UBLK_DBG_DEV, "%s enter\n", __func__);
- tinfo = calloc(sizeof(struct ublk_thread_info), dinfo->nr_hw_queues);
- tinfo = calloc(sizeof(struct ublk_thread_info), dev->nthreads); if (!tinfo) return -ENOMEM;
@@ -867,17 +895,24 @@ static int ublk_start_daemon(const struct dev_ctx *ctx, struct ublk_dev *dev) dinfo->dev_id, i); goto fail; }
- }
- for (i = 0; i < dev->nthreads; i++) { tinfo[i].dev = dev; tinfo[i].idx = i; tinfo[i].ready = &ready;
tinfo[i].affinity = &affinity_buf[i];
/** If threads are not tied to queues, setting thread* affinity based on queue affinity makes no sense.*/if (!(dinfo->flags & UBLK_F_RR_TAGS))tinfo[i].affinity = &affinity_buf[i];
- for (i = 0; i < dinfo->nr_hw_queues; i++)
- for (i = 0; i < dev->nthreads; i++) sem_wait(&ready); free(tinfo); free(affinity_buf);
@@ -901,7 +936,7 @@ static int ublk_start_daemon(const struct dev_ctx *ctx, struct ublk_dev *dev) ublk_send_dev_event(ctx, dev, dev->dev_info.dev_id); /* wait until we are terminated */
- for (i = 0; i < dinfo->nr_hw_queues; i++)
- for (i = 0; i < dev->nthreads; i++) pthread_join(dev->threads[i].thread, &thread_ret); fail: for (i = 0; i < dinfo->nr_hw_queues; i++)
@@ -1011,6 +1046,7 @@ static int ublk_stop_io_daemon(const struct ublk_dev *dev) static int __cmd_dev_add(const struct dev_ctx *ctx) {
- unsigned nthreads = ctx->nthreads; unsigned nr_queues = ctx->nr_hw_queues; const char *tgt_type = ctx->tgt_type; unsigned depth = ctx->queue_depth;
@@ -1034,6 +1070,23 @@ static int __cmd_dev_add(const struct dev_ctx *ctx) return -EINVAL; }
- /* default to 1:1 threads:queues if nthreads is unspecified */
- if (nthreads == -1)
nthreads = nr_queues;
Maybe we can start 1:1 for nrthreads == 0, which looks more readable, and you needn't to set -1 default.
- if (nthreads > UBLK_MAX_THREADS) {
ublk_err("%s: %u is too many threads (max %u)\n",__func__, nthreads, UBLK_MAX_THREADS);return -EINVAL;- }
- if (nthreads != nr_queues && !(ctx->flags & UBLK_F_RR_TAGS)) {
ublk_err("%s: threads %u must be same as queues %u if ""not using round robin\n",__func__, nthreads, nr_queues);return -EINVAL;- }
- dev = ublk_ctrl_init(); if (!dev) { ublk_err("%s: can't alloc dev id %d, type %s\n",
@@ -1054,6 +1107,7 @@ static int __cmd_dev_add(const struct dev_ctx *ctx) info->nr_hw_queues = nr_queues; info->queue_depth = depth; info->flags = ctx->flags;
- dev->nthreads = nthreads; dev->tgt.ops = ops; dev->tgt.sq_depth = depth; dev->tgt.cq_depth = depth;
@@ -1249,6 +1303,7 @@ static int cmd_dev_get_features(void) [const_ilog2(UBLK_F_USER_COPY)] = "USER_COPY", [const_ilog2(UBLK_F_ZONED)] = "ZONED", [const_ilog2(UBLK_F_USER_RECOVERY_FAIL_IO)] = "RECOVERY_FAIL_IO",
[const_ilog2(UBLK_F_RR_TAGS)] = "RR_TAGS",@@ -1290,8 +1345,10 @@ static void __cmd_create_help(char *exe, bool recovery) exe, recovery ? "recover" : "add"); printf("\t[--foreground] [--quiet] [-z] [--debug_mask mask] [-r 0|1 ] [-g]\n"); printf("\t[-e 0|1 ] [-i 0|1]\n");
- printf("\t[--nthreads threads] [--round_robin]\n"); printf("\t[target options] [backfile1] [backfile2] ...\n"); printf("\tdefault: nr_queues=2(max 32), depth=128(max 1024), dev_id=-1(auto allocation)\n");
- printf("\tdefault: nthreads=nr_queues");
for (i = 0; i < sizeof(tgt_ops_list) / sizeof(tgt_ops_list[0]); i++) { const struct ublk_tgt_ops *ops = tgt_ops_list[i]; @@ -1343,6 +1400,8 @@ int main(int argc, char *argv[]) { "recovery_fail_io", 1, NULL, 'e'}, { "recovery_reissue", 1, NULL, 'i'}, { "get_data", 1, NULL, 'g'},
{ "nthreads", 1, NULL, 0 },{ "round_robin", 0, NULL, 0 },@@ -1351,6 +1410,7 @@ int main(int argc, char *argv[]) struct dev_ctx ctx = { .queue_depth = 128, .nr_hw_queues = 2,
.nthreads = -1,@@ -1411,6 +1471,10 @@ int main(int argc, char *argv[]) ublk_dbg_mask = 0; if (!strcmp(longopts[option_idx].name, "foreground")) ctx.fg = 1;
if (!strcmp(longopts[option_idx].name, "nthreads"))ctx.nthreads = strtol(optarg, NULL, 10);if (!strcmp(longopts[option_idx].name, "round_robin"))ctx.flags |= UBLK_F_RR_TAGS;
maybe `--io_task` is more readable, and you can always enable UBLK_F_RR_TAGS for this '--io_task' ublk server feature.
Thanks, Ming