From: Pavel Begunkov <[email protected]>
To: Jens Axboe <[email protected]>, [email protected]
Subject: Re: [PATCH 4/4] io_uring: optimise compl locking for non-shared rings
Date: Fri, 18 Mar 2022 15:32:15 +0000 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
[-- Attachment #1: Type: text/plain, Size: 4067 bytes --]
On 3/18/22 15:21, Jens Axboe wrote:
> On 3/18/22 9:13 AM, Pavel Begunkov wrote:
>> On 3/18/22 14:54, Jens Axboe wrote:
>>> On 3/18/22 7:52 AM, Pavel Begunkov wrote:
>>>> When only one task submits requests, most of CQEs are expected to be
>>>> filled from that task context so we have natural serialisation. That
>>>> would mean that in those cases we don't need spinlocking around CQE
>>>> posting. One downside is that it also mean that io-wq workers can't emit
>>>> CQEs directly but should do it through the original task context using
>>>> task_works. That may hurt latency and performance and might matter much
>>>> to some workloads, but it's not a huge deal in general as io-wq is a
>>>> slow path and there is some additional merit from tw completion
>>>> batching.
>>>
>>> Not too worried about io-wq task_work for cq filling, it is the slower
>>> path after all. And I think we can get away with doing notifications as
>>> it's just for CQ filling. If the task is currently waiting in
>>> cqring_wait, then it'll get woken anyway and it will process task work.
>>> If it's in userspace, it doesn't need a notification. That should make
>>> it somewhat lighter than requiring using TIF_NOTIFY_SIGNAL for that.
>>>
>>>> The feature should be opted-in by the userspace by setting a new
>>>> IORING_SETUP_PRIVATE_CQ flag. It doesn't work with IOPOLL, and also for
>>>> now only the task that created a ring can submit requests to it.
>>>
>>> I know this is a WIP, but why do we need CQ_PRIVATE? And this needs to
>>
>> One reason is because of the io-wq -> tw punting, which is not optimal
>> for e.g. active users of IOSQE_ASYNC. The second is because the
>> fundamental requirement is that only one task should be submitting
>> requests. Was thinking about automating it, e.g. when we register
>> a second tctx we go through a slow path waiting for all current tw
>> to complete and then removing an internal and not userspace visible
>> CQ_PRIVATE flag.
>
> Was thinking something along those lines too. The alternative is setting
> up the ring with SETUP_SINGLE_ISSUER or something like that, having the
> application tell us that it is a single issuer and no submits are
> shared across threads. Serves the same kind of purpose as CQ_PRIVATE,
> but enables us to simply fail things if the task violates those
> constraints. Would also be a better name I believe as it might enable
> further optimizations in the future, like for example the mutex
> reduction for submits.
That's exactly what it is, including the failing part. And I like
your name better, will take it
>> Also, as SQPOLL task is by definition the only one submitting SQEs,
>> was thinking about enabling it by default for them, but didn't do
>> because of the io-wq / IOSQE_ASYNC.
>
> Gotcha.
>
>>> work with registered files (and ring fd) as that is probably a bigger
>>> win than skipping the completion_lock if you're not shared anyway.
>>
>> It does work with fixed/registered files and registered io_uring fds.
>
> t/io_uring fails for me with registered files or rings, getting EINVAL.
> Might be user error, but that's simply just setting CQ_PRIVATE for
> setup.
One thing I changed in the tool is that the ring should be created
by the submitter task, so move setup_ring into the submitter thread.
Plan to get rid of this restriction though.
Weird that it works only for you only without reg files/rings, will
take a look.
Attached io_uring.c that I used, it's based on some old version,
so do_nop can't be set in argv but should turned in the source code.
IORING_ENTER_REGISTERED_RING is always enabled.
>> In regards of "a bigger win", probably in many cases, but if you submit
>> a good batch at once, and completion tw batching doesn't kick in (e.g.
>> direct bdev read of not too high intensity), it might save
>> N spinlock/unlock when registered ring fd would kill only one pair of
>> fdget/fdput.
>
> Definitely, various cases where one would be a bigger win than the
> other, agree on that. But let's just ensure that both work together :-)
--
Pavel Begunkov
[-- Attachment #2: io_uring.c --]
[-- Type: text/x-csrc, Size: 15194 bytes --]
#include <stdio.h>
#include <errno.h>
#include <assert.h>
#include <stdlib.h>
#include <stddef.h>
#include <signal.h>
#include <inttypes.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#include <sys/resource.h>
#include <sys/mman.h>
#include <sys/uio.h>
#include <linux/fs.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <pthread.h>
#include <sched.h>
#include "../arch/arch.h"
#include "../lib/types.h"
#include "../os/linux/io_uring.h"
#define min(a, b) ((a < b) ? (a) : (b))
struct io_sq_ring {
unsigned *head;
unsigned *tail;
unsigned *ring_mask;
unsigned *ring_entries;
unsigned *flags;
unsigned *array;
};
#define IORING_SETUP_PRIVATE_CQ (1U << 8)
enum {
IORING_REGISTER_RING_FDS = 20,
};
#define IORING_ENTER_REGISTERED_RING (1U << 4)
struct io_cq_ring {
unsigned *head;
unsigned *tail;
unsigned *ring_mask;
unsigned *ring_entries;
struct io_uring_cqe *cqes;
};
#define DEPTH 128
#define BATCH_SUBMIT 32
#define BATCH_COMPLETE 32
#define BS 4096
#define MAX_FDS 16
static unsigned sq_ring_mask, cq_ring_mask;
struct file {
unsigned long max_blocks;
unsigned pending_ios;
int real_fd;
int fixed_fd;
};
struct submitter {
pthread_t thread;
int ring_fd;
struct io_sq_ring sq_ring;
struct io_uring_sqe *sqes;
struct io_cq_ring cq_ring;
int inflight;
unsigned long reaps;
unsigned long done;
unsigned long calls;
volatile int finish;
__s32 *fds;
struct file files[MAX_FDS];
unsigned nr_files;
unsigned cur_file;
struct iovec iovecs[];
};
static struct submitter *submitter;
static volatile int finish;
static int depth = DEPTH;
static int batch_submit = BATCH_SUBMIT;
static int batch_complete = BATCH_COMPLETE;
static int bs = BS;
static int polled = 1; /* use IO polling */
static int fixedbufs = 1; /* use fixed user buffers */
static int register_files = 1; /* use fixed files */
static int buffered = 0; /* use buffered IO, not O_DIRECT */
static int sq_thread_poll = 0; /* use kernel submission/poller thread */
static int sq_thread_cpu = -1; /* pin above thread to this CPU */
static int do_nop = 1; /* no-op SQ ring commands */
struct io_uring_rsrc_update {
__u32 offset;
__u32 resv;
__aligned_u64 data;
};
static int vectored = 1;
static int setup_ring(struct submitter *s);
static int io_uring_register_buffers(struct submitter *s)
{
if (do_nop)
return 0;
return syscall(__NR_io_uring_register, s->ring_fd,
IORING_REGISTER_BUFFERS, s->iovecs, depth);
}
static int io_uring_register_io_uring_fd(struct submitter *s)
{
struct io_uring_rsrc_update up = {};
up.offset = 0;
up.data = s->ring_fd;
return syscall(__NR_io_uring_register, s->ring_fd,
IORING_REGISTER_RING_FDS, &up, 1);
}
static int io_uring_register_files(struct submitter *s)
{
int i;
if (do_nop)
return 0;
s->fds = calloc(s->nr_files, sizeof(__s32));
for (i = 0; i < s->nr_files; i++) {
s->fds[i] = s->files[i].real_fd;
s->files[i].fixed_fd = i;
}
return syscall(__NR_io_uring_register, s->ring_fd,
IORING_REGISTER_FILES, s->fds, s->nr_files);
}
static int io_uring_setup(unsigned entries, struct io_uring_params *p)
{
return syscall(__NR_io_uring_setup, entries, p);
}
static void io_uring_probe(int fd)
{
struct io_uring_probe *p;
int ret;
p = malloc(sizeof(*p) + 256 * sizeof(struct io_uring_probe_op));
if (!p)
return;
memset(p, 0, sizeof(*p) + 256 * sizeof(struct io_uring_probe_op));
ret = syscall(__NR_io_uring_register, fd, IORING_REGISTER_PROBE, p, 256);
if (ret < 0)
goto out;
if (IORING_OP_READ > p->ops_len)
goto out;
if ((p->ops[IORING_OP_READ].flags & IO_URING_OP_SUPPORTED))
vectored = 0;
out:
free(p);
}
static int io_uring_enter(struct submitter *s, unsigned int to_submit,
unsigned int min_complete, unsigned int flags)
{
return syscall(__NR_io_uring_enter, 0, to_submit, min_complete,
flags | IORING_ENTER_REGISTERED_RING, NULL, 0);
}
#ifndef CONFIG_HAVE_GETTID
static int gettid(void)
{
return syscall(__NR_gettid);
}
#endif
static unsigned file_depth(struct submitter *s)
{
return (depth + s->nr_files - 1) / s->nr_files;
}
static void init_io(struct submitter *s, unsigned index)
{
struct io_uring_sqe *sqe = &s->sqes[index];
unsigned long offset;
struct file *f;
long r;
if (do_nop) {
sqe->opcode = IORING_OP_NOP;
return;
}
if (s->nr_files == 1) {
f = &s->files[0];
} else {
f = &s->files[s->cur_file];
if (f->pending_ios >= file_depth(s)) {
s->cur_file++;
if (s->cur_file == s->nr_files)
s->cur_file = 0;
f = &s->files[s->cur_file];
}
}
f->pending_ios++;
r = lrand48();
offset = (r % (f->max_blocks - 1)) * bs;
if (register_files) {
sqe->flags = IOSQE_FIXED_FILE;
sqe->fd = f->fixed_fd;
} else {
sqe->flags = 0;
sqe->fd = f->real_fd;
}
if (fixedbufs) {
sqe->opcode = IORING_OP_READ_FIXED;
sqe->addr = (unsigned long) s->iovecs[index].iov_base;
sqe->len = bs;
sqe->buf_index = index;
} else if (!vectored) {
sqe->opcode = IORING_OP_READ;
sqe->addr = (unsigned long) s->iovecs[index].iov_base;
sqe->len = bs;
sqe->buf_index = 0;
} else {
sqe->opcode = IORING_OP_READV;
sqe->addr = (unsigned long) &s->iovecs[index];
sqe->len = 1;
sqe->buf_index = 0;
}
sqe->ioprio = 0;
sqe->off = offset;
sqe->user_data = (unsigned long) f;
}
static int prep_more_ios(struct submitter *s, int max_ios)
{
struct io_sq_ring *ring = &s->sq_ring;
unsigned index, tail, next_tail, prepped = 0;
next_tail = tail = *ring->tail;
do {
next_tail++;
if (next_tail == atomic_load_acquire(ring->head))
break;
index = tail & sq_ring_mask;
init_io(s, index);
ring->array[index] = index;
prepped++;
tail = next_tail;
} while (prepped < max_ios);
if (prepped)
atomic_store_release(ring->tail, tail);
return prepped;
}
static int get_file_size(struct file *f)
{
struct stat st;
if (fstat(f->real_fd, &st) < 0)
return -1;
if (S_ISBLK(st.st_mode)) {
unsigned long long bytes;
if (ioctl(f->real_fd, BLKGETSIZE64, &bytes) != 0)
return -1;
f->max_blocks = bytes / bs;
return 0;
} else if (S_ISREG(st.st_mode)) {
f->max_blocks = st.st_size / bs;
return 0;
}
return -1;
}
static int reap_events(struct submitter *s)
{
struct io_cq_ring *ring = &s->cq_ring;
struct io_uring_cqe *cqe;
unsigned head, reaped = 0;
head = *ring->head;
do {
struct file *f;
read_barrier();
if (head == atomic_load_acquire(ring->tail))
break;
cqe = &ring->cqes[head & cq_ring_mask];
if (!do_nop) {
f = (struct file *) (uintptr_t) cqe->user_data;
f->pending_ios--;
if (cqe->res != bs) {
printf("io: unexpected ret=%d\n", cqe->res);
if (polled && cqe->res == -EOPNOTSUPP)
printf("Your filesystem/driver/kernel doesn't support polled IO\n");
return -1;
}
}
reaped++;
head++;
} while (1);
if (reaped) {
s->inflight -= reaped;
atomic_store_release(ring->head, head);
}
return reaped;
}
static void *submitter_fn(void *data)
{
struct submitter *s = data;
struct io_sq_ring *ring = &s->sq_ring;
int ret, prepped;
ret = setup_ring(s);
if (ret) {
printf("ring setup failed: %s, %d\n", strerror(errno), ret);
return NULL;
}
printf("submitter=%d\n", gettid());
srand48(pthread_self());
prepped = 0;
do {
int to_wait, to_submit, this_reap, to_prep;
unsigned ring_flags = 0;
if (!prepped && s->inflight < depth) {
to_prep = min(depth - s->inflight, batch_submit);
prepped = prep_more_ios(s, to_prep);
}
s->inflight += prepped;
submit_more:
to_submit = prepped;
submit:
if (to_submit && (s->inflight + to_submit <= depth))
to_wait = 0;
else
to_wait = min(s->inflight + to_submit, batch_complete);
/*
* Only need to call io_uring_enter if we're not using SQ thread
* poll, or if IORING_SQ_NEED_WAKEUP is set.
*/
if (sq_thread_poll)
ring_flags = atomic_load_acquire(ring->flags);
if (!sq_thread_poll || ring_flags & IORING_SQ_NEED_WAKEUP) {
unsigned flags = 0;
if (to_wait)
flags = IORING_ENTER_GETEVENTS;
if (ring_flags & IORING_SQ_NEED_WAKEUP)
flags |= IORING_ENTER_SQ_WAKEUP;
ret = io_uring_enter(s, to_submit, to_wait, flags);
s->calls++;
} else {
/* for SQPOLL, we submitted it all effectively */
ret = to_submit;
}
/*
* For non SQ thread poll, we already got the events we needed
* through the io_uring_enter() above. For SQ thread poll, we
* need to loop here until we find enough events.
*/
this_reap = 0;
do {
int r;
r = reap_events(s);
if (r == -1) {
s->finish = 1;
break;
} else if (r > 0)
this_reap += r;
} while (sq_thread_poll && this_reap < to_wait);
s->reaps += this_reap;
if (ret >= 0) {
if (!ret) {
to_submit = 0;
if (s->inflight)
goto submit;
continue;
} else if (ret < to_submit) {
int diff = to_submit - ret;
s->done += ret;
prepped -= diff;
goto submit_more;
}
s->done += ret;
prepped = 0;
continue;
} else if (ret < 0) {
if (errno == EAGAIN) {
if (s->finish)
break;
if (this_reap)
goto submit;
to_submit = 0;
goto submit;
}
printf("io_submit: %s\n", strerror(errno));
break;
}
} while (!s->finish);
finish = 1;
return NULL;
}
static void sig_int(int sig)
{
printf("Exiting on signal %d\n", sig);
submitter->finish = 1;
finish = 1;
}
static void arm_sig_int(void)
{
struct sigaction act;
memset(&act, 0, sizeof(act));
act.sa_handler = sig_int;
act.sa_flags = SA_RESTART;
sigaction(SIGINT, &act, NULL);
}
static int setup_ring(struct submitter *s)
{
struct io_sq_ring *sring = &s->sq_ring;
struct io_cq_ring *cring = &s->cq_ring;
struct io_uring_params p;
int ret, fd;
void *ptr;
memset(&p, 0, sizeof(p));
if (polled && !do_nop)
p.flags |= IORING_SETUP_IOPOLL;
if (sq_thread_poll) {
p.flags |= IORING_SETUP_SQPOLL;
if (sq_thread_cpu != -1) {
p.flags |= IORING_SETUP_SQ_AFF;
p.sq_thread_cpu = sq_thread_cpu;
}
}
p.flags |= IORING_SETUP_PRIVATE_CQ;
fd = io_uring_setup(depth, &p);
if (fd < 0) {
perror("io_uring_setup");
return 1;
}
s->ring_fd = fd;
io_uring_probe(fd);
ret = io_uring_register_io_uring_fd(s);
if (ret < 0) {
perror("io_uring_register_io_uring_fd");
return 1;
}
if (fixedbufs) {
ret = io_uring_register_buffers(s);
if (ret < 0) {
perror("io_uring_register_buffers");
return 1;
}
}
if (register_files) {
ret = io_uring_register_files(s);
if (ret < 0) {
perror("io_uring_register_files");
return 1;
}
}
ptr = mmap(0, p.sq_off.array + p.sq_entries * sizeof(__u32),
PROT_READ | PROT_WRITE, MAP_SHARED | MAP_POPULATE, fd,
IORING_OFF_SQ_RING);
printf("sq_ring ptr = 0x%p\n", ptr);
sring->head = ptr + p.sq_off.head;
sring->tail = ptr + p.sq_off.tail;
sring->ring_mask = ptr + p.sq_off.ring_mask;
sring->ring_entries = ptr + p.sq_off.ring_entries;
sring->flags = ptr + p.sq_off.flags;
sring->array = ptr + p.sq_off.array;
sq_ring_mask = *sring->ring_mask;
s->sqes = mmap(0, p.sq_entries * sizeof(struct io_uring_sqe),
PROT_READ | PROT_WRITE, MAP_SHARED | MAP_POPULATE, fd,
IORING_OFF_SQES);
printf("sqes ptr = 0x%p\n", s->sqes);
ptr = mmap(0, p.cq_off.cqes + p.cq_entries * sizeof(struct io_uring_cqe),
PROT_READ | PROT_WRITE, MAP_SHARED | MAP_POPULATE, fd,
IORING_OFF_CQ_RING);
printf("cq_ring ptr = 0x%p\n", ptr);
cring->head = ptr + p.cq_off.head;
cring->tail = ptr + p.cq_off.tail;
cring->ring_mask = ptr + p.cq_off.ring_mask;
cring->ring_entries = ptr + p.cq_off.ring_entries;
cring->cqes = ptr + p.cq_off.cqes;
cq_ring_mask = *cring->ring_mask;
return 0;
}
static void file_depths(char *buf)
{
struct submitter *s = submitter;
char *p;
int i;
buf[0] = '\0';
p = buf;
for (i = 0; i < s->nr_files; i++) {
struct file *f = &s->files[i];
if (i + 1 == s->nr_files)
p += sprintf(p, "%d", f->pending_ios);
else
p += sprintf(p, "%d, ", f->pending_ios);
}
}
static void usage(char *argv)
{
printf("%s [options] -- [filenames]\n"
" -d <int> : IO Depth, default %d\n"
" -s <int> : Batch submit, default %d\n"
" -c <int> : Batch complete, default %d\n"
" -b <int> : Block size, default %d\n"
" -p <bool> : Polled IO, default %d\n",
argv, DEPTH, BATCH_SUBMIT, BATCH_COMPLETE, BS, polled);
exit(0);
}
int main(int argc, char *argv[])
{
struct submitter *s;
unsigned long done, calls, reap;
int i, flags, fd, opt;
char *fdepths;
void *ret;
if (!do_nop && argc < 2) {
printf("%s: filename [options]\n", argv[0]);
return 1;
}
while ((opt = getopt(argc, argv, "d:s:c:b:p:B:F:h?")) != -1) {
switch (opt) {
case 'd':
depth = atoi(optarg);
break;
case 's':
batch_submit = atoi(optarg);
break;
case 'c':
batch_complete = atoi(optarg);
break;
case 'b':
bs = atoi(optarg);
break;
case 'p':
polled = !!atoi(optarg);
break;
case 'B':
fixedbufs = !!atoi(optarg);
break;
case 'F':
register_files = !!atoi(optarg);
break;
case 'h':
case '?':
default:
usage(argv[0]);
break;
}
}
submitter = malloc(sizeof(*submitter) + depth * sizeof(struct iovec));
memset(submitter, 0, sizeof(*submitter) + depth * sizeof(struct iovec));
s = submitter;
flags = O_RDONLY | O_NOATIME;
if (!buffered)
flags |= O_DIRECT;
i = optind;
while (!do_nop && i < argc) {
struct file *f;
if (s->nr_files == MAX_FDS) {
printf("Max number of files (%d) reached\n", MAX_FDS);
break;
}
fd = open(argv[i], flags);
if (fd < 0) {
perror("open");
return 1;
}
f = &s->files[s->nr_files];
f->real_fd = fd;
if (get_file_size(f)) {
printf("failed getting size of device/file\n");
return 1;
}
if (f->max_blocks <= 1) {
printf("Zero file/device size?\n");
return 1;
}
f->max_blocks--;
printf("Added file %s\n", argv[i]);
s->nr_files++;
i++;
}
if (fixedbufs) {
struct rlimit rlim;
rlim.rlim_cur = RLIM_INFINITY;
rlim.rlim_max = RLIM_INFINITY;
if (setrlimit(RLIMIT_MEMLOCK, &rlim) < 0) {
perror("setrlimit");
return 1;
}
}
arm_sig_int();
for (i = 0; i < depth; i++) {
void *buf;
if (posix_memalign(&buf, bs, bs)) {
printf("failed alloc\n");
return 1;
}
s->iovecs[i].iov_base = buf;
s->iovecs[i].iov_len = bs;
}
printf("polled=%d, fixedbufs=%d, register_files=%d, buffered=%d", polled, fixedbufs, register_files, buffered);
printf(" QD=%d, sq_ring=%d, cq_ring=%d\n", depth, 0, 0);
pthread_create(&s->thread, NULL, submitter_fn, s);
fdepths = malloc(8 * s->nr_files);
reap = calls = done = 0;
do {
unsigned long this_done = 0;
unsigned long this_reap = 0;
unsigned long this_call = 0;
unsigned long rpc = 0, ipc = 0;
sleep(1);
this_done += s->done;
this_call += s->calls;
this_reap += s->reaps;
if (this_call - calls) {
rpc = (this_done - done) / (this_call - calls);
ipc = (this_reap - reap) / (this_call - calls);
} else
rpc = ipc = -1;
file_depths(fdepths);
printf("IOPS=%lu, IOS/call=%ld/%ld, inflight=%u (%s)\n",
this_done - done, rpc, ipc, s->inflight,
fdepths);
done = this_done;
calls = this_call;
reap = this_reap;
} while (!finish);
pthread_join(s->thread, &ret);
close(s->ring_fd);
free(fdepths);
return 0;
}
next prev parent reply other threads:[~2022-03-18 15:34 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-18 13:52 [RFC 0/4] completion locking optimisation feature Pavel Begunkov
2022-03-18 13:52 ` [PATCH 1/4] io_uring: get rid of raw fill cqe in kill_timeout Pavel Begunkov
2022-03-18 13:52 ` [PATCH 2/4] io_uring: get rid of raw fill_cqe in io_fail_links Pavel Begunkov
2022-03-18 13:52 ` [PATCH 3/4] io_uring: remove raw fill_cqe from linked timeout Pavel Begunkov
2022-03-18 13:52 ` [PATCH 4/4] io_uring: optimise compl locking for non-shared rings Pavel Begunkov
2022-03-18 14:54 ` Jens Axboe
2022-03-18 15:13 ` Pavel Begunkov
2022-03-18 15:21 ` Jens Axboe
2022-03-18 15:32 ` Pavel Begunkov [this message]
2022-03-18 16:06 ` Jens Axboe
2022-03-18 14:42 ` [RFC 0/4] completion locking optimisation feature Pavel Begunkov
2022-03-18 14:52 ` Jens Axboe
2022-03-18 15:00 ` Pavel Begunkov
2022-03-18 15:22 ` Jens Axboe
2022-03-18 15:34 ` Pavel Begunkov
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