[PATCH 27/27] libxfs: convert sync IO buftarg engine to AIO

Dave Chinner
2020-10-15T07:22:27Z

Simple per-ag thread based completion engine. Will have issues with
large AG counts.

XXX: should this be combined with the struct btcache?

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
include/atomic.h | 7 +-
include/builddefs.in | 2 +-
include/platform_defs.h.in | 1 +
libxfs/buftarg.c | 202 +++++++++++++++++++++++++++++++------
libxfs/xfs_buf.h | 6 ++
libxfs/xfs_buftarg.h | 7 ++
6 files changed, 191 insertions(+), 34 deletions(-)

diff --git a/include/atomic.h b/include/atomic.h
index 5860d7897ae5..8727fc4ddae9 100644
--- a/include/atomic.h
+++ b/include/atomic.h
@@ -27,8 +27,11 @@ typedef int64_t atomic64_t;
#define atomic_inc_return(a) uatomic_add_return(a, 1)
#define atomic_dec_return(a) uatomic_sub_return(a, 1)

-#define atomic_inc(a) atomic_inc_return(a)
-#define atomic_dec(a) atomic_inc_return(a)
+#define atomic_add(a, v) uatomic_add(a, v)
+#define atomic_sub(a, v) uatomic_sub(a, v)
+
+#define atomic_inc(a) uatomic_inc(a)
+#define atomic_dec(a) uatomic_dec(a)

#define atomic_dec_and_test(a) (atomic_dec_return(a) == 0)

diff --git a/include/builddefs.in b/include/builddefs.in
index 78eddf4a9852..c20a48f6258c 100644
--- a/include/builddefs.in
+++ b/include/builddefs.in
@@ -29,7 +29,7 @@ LIBEDITLINE = @libeditline@
LIBBLKID = @libblkid@
LIBDEVMAPPER = @libdevmapper@
LIBINIH = @libinih@
-LIBXFS = $(TOPDIR)/libxfs/libxfs.la
+LIBXFS = $(TOPDIR)/libxfs/libxfs.la -laio
LIBFROG = $(TOPDIR)/libfrog/libfrog.la
LIBXCMD = $(TOPDIR)/libxcmd/libxcmd.la
LIBXLOG = $(TOPDIR)/libxlog/libxlog.la
diff --git a/include/platform_defs.h.in b/include/platform_defs.h.in
index 8af43f3b8d8a..7c30a43eb951 100644
--- a/include/platform_defs.h.in
+++ b/include/platform_defs.h.in
@@ -24,6 +24,7 @@
#include <stdbool.h>
#include <libgen.h>
#include <urcu.h>
+#include <libaio.h>

typedef struct filldir filldir_t;

diff --git a/libxfs/buftarg.c b/libxfs/buftarg.c
index df968c66c205..e1e5f41b423c 100644
--- a/libxfs/buftarg.c
+++ b/libxfs/buftarg.c
@@ -259,11 +259,16 @@ xfs_buftarg_alloc(
if (percpu_counter_init(&btp->bt_io_count, 0, GFP_KERNEL))
goto error_lru;

- if (xfs_buftarg_mempressue_init(btp))
+ if (xfs_buftarg_aio_init(&btp->bt_aio))
goto error_pcp;

+ if (xfs_buftarg_mempressue_init(btp))
+ goto error_aio;
+
return btp;

+error_aio:
+ xfs_buftarg_aio_destroy(btp->bt_aio);
error_pcp:
percpu_counter_destroy(&btp->bt_io_count);
error_lru:
@@ -286,6 +291,7 @@ xfs_buftarg_free(
if (btp->bt_psi_fd >= 0)
close(btp->bt_psi_fd);

+ xfs_buftarg_aio_destroy(btp->bt_aio);
ASSERT(percpu_counter_sum(&btp->bt_io_count) == 0);
percpu_counter_destroy(&btp->bt_io_count);
platform_flush_device(btp->bt_fd, btp->bt_bdev);
@@ -329,39 +335,132 @@ xfs_buf_allocate_memory(
*/

/*
- * XXX: this will be replaced by an AIO submission engine in future. In the mean
- * time, just complete the IO synchronously so all the machinery still works.
+ * AIO context for dispatch and completion.
+ *
+ * Run completion polling in a separate thread, the poll timeout will stop it
+ * from spinning in tight loops when there is nothing to do.
*/
-static int
-submit_io(
- struct xfs_buf *bp,
- int fd,
- void *buf,
- xfs_daddr_t blkno,
- int size,
- bool write)
+#define MAX_AIO_EVENTS 1024
+struct xfs_btaio {
+ io_context_t ctxp;
+ int aio_fd;
+ int aio_in_flight;
+ pthread_t completion_tid;
+ bool done;
+};
+
+static void
+xfs_buf_aio_ioend(
+ struct io_event *ev)
{
- int ret;
+ struct xfs_buf *bp = (struct xfs_buf *)ev->data;

- if (!write)
- ret = pread(fd, buf, size, BBTOB(blkno));
- else
- ret = pwrite(fd, buf, size, BBTOB(blkno));
- if (ret < 0)
- ret = -errno;
- else if (ret != size)
- ret = -EIO;
- else
- ret = 0;
/*
- * This is a bit of a hack until we get AIO that runs completions.
- * Success is treated as a completion here, but IO errors are handled as
- * a submission error and are handled by the caller. AIO will clean this
- * up.
+ * don't overwrite existing errors - otherwise we can lose errors on
+ * buffers that require multiple bios to complete.
+ *
+ * We check that the returned length was the same as specified for this
+ * IO. Note that this onyl works for read and write - if we start
+ * using readv/writev for discontiguous buffers then this needs more
+ * work.
*/
- if (!ret)
+ if (ev->res < 0 || ev->res != ev->obj->u.c.nbytes) {
+ int error = ev->res < 0 ? (int)ev->res : -EIO;
+
+ cmpxchg(&bp->b_io_error, 0, error);
+ }
+
+ if (atomic_dec_and_test(&bp->b_io_remaining))
xfs_buf_ioend(bp);
- return ret;
+}
+
+static void
+get_io_completions(
+ struct xfs_btaio *aio,
+ int threshold)
+{
+ struct io_event ioevents[MAX_AIO_EVENTS];
+ struct timespec tout = {
+ .tv_nsec = 100*1000*1000, /* 100ms */
+ };
+ int i, r;
+
+ /* gather up some completions */
+ r = io_getevents(aio->ctxp, 1, MAX_AIO_EVENTS, ioevents, &tout);
+ if (r < 0) {
+ fprintf(stderr, "FAIL! io_getevents returned %d\n", r);
+ if (r == -EINTR)
+ return;
+ exit(1);
+ }
+ if (r == 0) {
+ /* timeout, return to caller to check for what to do next */
+ return;
+ }
+
+ atomic_sub(&aio->aio_in_flight, r);
+ for (i = 0; i < r; ++i)
+ xfs_buf_aio_ioend(&ioevents[i]);
+}
+
+static void *
+aio_completion_thread(
+ void *arg)
+{
+ struct xfs_btaio *aio = arg;
+
+ while (!aio->done) {
+ get_io_completions(aio, 1);
+ }
+ return NULL;
+}
+
+static int
+submit_aio(
+ struct xfs_buf *bp,
+ void *buf,
+ xfs_daddr_t blkno,
+ int size)
+{
+ struct xfs_btaio *aio = bp->b_target->bt_aio;
+ int r;
+
+ if (!aio->aio_fd)
+ aio->aio_fd = bp->b_target->bt_fd;
+
+ /*
+ * Reserve and bound the number of in flight IOs to keep the number of
+ * pending IOs overrunning the tail of the event loop. This also serves
+ * to throttle incoming IOs without burning CPU by spinning.
+ */
+ while (!atomic_add_unless(&aio->aio_in_flight, 1, MAX_AIO_EVENTS - 1))
+ get_io_completions(aio, 1);
+
+ if (bp->b_flags & XBF_WRITE)
+ io_prep_pwrite(&bp->b_iocb, aio->aio_fd, buf, size, BBTOB(blkno));
+ else
+ io_prep_pread(&bp->b_iocb, aio->aio_fd, buf, size, BBTOB(blkno));
+
+ bp->b_iocb.data = bp;
+ do {
+ struct iocb *iocb;
+
+ iocb = &bp->b_iocb;
+ r = io_submit(aio->ctxp, 1, &iocb);
+ if (r == 1)
+ return 0; /* successful submission */
+ fprintf(stderr, "io_submit returned %d\n", r);
+ if (r != -EAGAIN)
+ break;
+ /* On EAGAIN, reap some completions and try again. */
+ get_io_completions(aio, 1);
+ } while (1);
+
+ if (bp->b_flags & LIBXFS_B_EXIT)
+ exit(1);
+
+ atomic_dec(&aio->aio_in_flight);
+ return r;
}

static void
@@ -373,7 +472,6 @@ xfs_buftarg_submit_io_map(
{
int size;
int offset;
- bool rw = (bp->b_flags & XBF_WRITE);
int error;

offset = *buf_offset;
@@ -388,8 +486,7 @@ xfs_buftarg_submit_io_map(

atomic_inc(&bp->b_io_remaining);

- error = submit_io(bp, bp->b_target->bt_fd, bp->b_addr + offset,
- bp->b_maps[map].bm_bn, size, rw);
+ error = submit_aio(bp, bp->b_addr + offset, bp->b_maps[map].bm_bn, size);
if (error) {
/*
* This is guaranteed not to be the last io reference count
@@ -474,6 +571,49 @@ xfs_buftarg_submit_io(
}
}

+int
+xfs_buftarg_aio_init(
+ struct xfs_btaio **aiop)
+{
+ struct xfs_btaio *aio;
+ int r;
+
+ aio = calloc(1, sizeof(*aio));
+ if (!aio)
+ return -ENOMEM;
+
+ r = io_setup(MAX_AIO_EVENTS, &aio->ctxp);
+ if (r) {
+ printf("FAIL! io_setup returned %d\n", r);
+ goto free_aio;
+ }
+
+ r = pthread_create(&aio->completion_tid, NULL, aio_completion_thread,
+ aio);
+ if (r) {
+ printf("FAIL! aio thread create returned %d\n", r);
+ goto free_aio;
+ }
+
+ *aiop = aio;
+ return 0;
+
+free_aio:
+ free(aio);
+ return r;
+}
+
+void
+xfs_buftarg_aio_destroy(
+ struct xfs_btaio *aio)
+{
+ if (!aio)
+ return;
+
+ aio->done = true;
+ pthread_join(aio->completion_tid, NULL);
+ free(aio);
+}
/*
* Return a buffer associated to external memory via xfs_buf_associate_memory()
* back to it's empty state.
diff --git a/libxfs/xfs_buf.h b/libxfs/xfs_buf.h
index 4b6dff885165..29fbaaab4abb 100644
--- a/libxfs/xfs_buf.h
+++ b/libxfs/xfs_buf.h
@@ -81,6 +81,12 @@ struct xfs_buf {
struct completion b_iowait;
struct semaphore b_sema;
xfs_buf_iodone_t b_iodone;
+
+ /*
+ * XXX: AIO needs as many iocbs as we have maps for discontig
+ * buffers to work correctly.
+ */
+ struct iocb b_iocb;
};

struct xfs_buf *xfs_buf_incore(struct xfs_buftarg *target,
diff --git a/libxfs/xfs_buftarg.h b/libxfs/xfs_buftarg.h
index 61c4a3164d23..62aa6f236537 100644
--- a/libxfs/xfs_buftarg.h
+++ b/libxfs/xfs_buftarg.h
@@ -16,6 +16,7 @@ struct xfs_buf_ops;
struct xfs_buf;
struct xfs_buf_map;
struct xfs_mount;
+struct xfs_btaio;

/* this needs to die */
#define LIBXFS_BBTOOFF64(bbs) (((xfs_off_t)(bbs)) << BBSHIFT)
@@ -55,6 +56,9 @@ struct xfs_buftarg {
bool bt_exiting;
bool bt_low_mem;
struct completion bt_low_mem_wait;
+
+ /* AIO submission/completion structures */
+ struct xfs_btaio *bt_aio;
};

/* We purged a dirty buffer and lost a write. */
@@ -90,6 +94,9 @@ int xfs_buf_associate_memory(struct xfs_buf *bp, void *mem, size_t length);
void xfs_buftarg_submit_io(struct xfs_buf *bp);
void xfs_buf_mark_dirty(struct xfs_buf *bp);

+int xfs_buftarg_aio_init(struct xfs_btaio **aiop);
+void xfs_buftarg_aio_destroy(struct xfs_btaio *aio);
+
/*
* Cached buffer memory manangement
*/
--
2.28.0