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io_uring: cache task struct refs

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tctx in submission part is always synchronised because is executed from
the task's context, so we can batch allocate tctx/task references and
store them across syscall boundaries. It avoids enough of operations,
including an atomic for getting task ref and a percpu_counter_add()
function call, which still fallback to spinlock for large batching
cases (around >=32). Should be good for SQPOLL submitting in small
portions and coming at some moment bpf submissions.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/14b327b973410a3eec1f702ecf650e100513aca9.1623634181.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2021-06-14 02:36:22 +01:00 committed by Jens Axboe
parent 2d091d62b1
commit 09899b1915
1 changed files with 28 additions and 9 deletions
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37
fs/io_uring.c
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@ -110,6 +110,8 @@
IOSQE_IO_HARDLINK | IOSQE_ASYNC | \
IOSQE_BUFFER_SELECT)
#define IO_TCTX_REFS_CACHE_NR (1U << 10)
struct io_uring {
u32 head ____cacheline_aligned_in_smp;
u32 tail ____cacheline_aligned_in_smp;
@ -472,6 +474,7 @@ struct io_ring_ctx {
struct io_uring_task {
/* submission side */
int cached_refs;
struct xarray xa;
struct wait_queue_head wait;
const struct io_ring_ctx *last;
@ -6707,16 +6710,23 @@ static const struct io_uring_sqe *io_get_sqe(struct io_ring_ctx *ctx)
static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr)
{
struct io_uring_task *tctx;
int submitted = 0;
/* make sure SQ entry isn't read before tail */
nr = min3(nr, ctx->sq_entries, io_sqring_entries(ctx));
if (!percpu_ref_tryget_many(&ctx->refs, nr))
return -EAGAIN;
percpu_counter_add(&current->io_uring->inflight, nr);
refcount_add(nr, &current->usage);
tctx = current->io_uring;
tctx->cached_refs -= nr;
if (unlikely(tctx->cached_refs < 0)) {
unsigned int refill = -tctx->cached_refs + IO_TCTX_REFS_CACHE_NR;
percpu_counter_add(&tctx->inflight, refill);
refcount_add(refill, &current->usage);
tctx->cached_refs += refill;
}
io_submit_state_start(&ctx->submit_state, nr);
while (submitted < nr) {
@ -6742,12 +6752,10 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr)
if (unlikely(submitted != nr)) {
int ref_used = (submitted == -EAGAIN) ? 0 : submitted;
struct io_uring_task *tctx = current->io_uring;
int unused = nr - ref_used;
current->io_uring->cached_refs += unused;
percpu_ref_put_many(&ctx->refs, unused);
percpu_counter_sub(&tctx->inflight, unused);
put_task_struct_many(current, unused);
}
io_submit_state_end(&ctx->submit_state, ctx);
@ -7929,7 +7937,7 @@ static int io_uring_alloc_task_context(struct task_struct *task,
struct io_uring_task *tctx;
int ret;
tctx = kmalloc(sizeof(*tctx), GFP_KERNEL);
tctx = kzalloc(sizeof(*tctx), GFP_KERNEL);
if (unlikely(!tctx))
return -ENOMEM;
@ -7949,13 +7957,11 @@ static int io_uring_alloc_task_context(struct task_struct *task,
xa_init(&tctx->xa);
init_waitqueue_head(&tctx->wait);
tctx->last = NULL;
atomic_set(&tctx->in_idle, 0);
atomic_set(&tctx->inflight_tracked, 0);
task->io_uring = tctx;
spin_lock_init(&tctx->task_lock);
INIT_WQ_LIST(&tctx->task_list);
tctx->task_state = 0;
init_task_work(&tctx->task_work, tctx_task_work);
return 0;
}
@ -7966,6 +7972,7 @@ void __io_uring_free(struct task_struct *tsk)
WARN_ON_ONCE(!xa_empty(&tctx->xa));
WARN_ON_ONCE(tctx->io_wq);
WARN_ON_ONCE(tctx->cached_refs);
percpu_counter_destroy(&tctx->inflight);
kfree(tctx);
@ -9110,6 +9117,16 @@ static void io_uring_try_cancel(bool cancel_all)
}
}
static void io_uring_drop_tctx_refs(struct task_struct *task)
{
struct io_uring_task *tctx = task->io_uring;
unsigned int refs = tctx->cached_refs;
tctx->cached_refs = 0;
percpu_counter_sub(&tctx->inflight, refs);
put_task_struct_many(task, refs);
}
/* should only be called by SQPOLL task */
static void io_uring_cancel_sqpoll(struct io_sq_data *sqd)
{
@ -9125,6 +9142,7 @@ static void io_uring_cancel_sqpoll(struct io_sq_data *sqd)
WARN_ON_ONCE(!sqd || sqd->thread != current);
io_uring_drop_tctx_refs(current);
atomic_inc(&tctx->in_idle);
do {
/* read completions before cancelations */
@ -9162,6 +9180,7 @@ void __io_uring_cancel(struct files_struct *files)
io_wq_exit_start(tctx->io_wq);
/* make sure overflow events are dropped */
io_uring_drop_tctx_refs(current);
atomic_inc(&tctx->in_idle);
do {
/* read completions before cancelations */