* [Qemu-devel] [PATCH v9 1/2] mirror: Rewrite mirror_iteration
2016-01-05 8:46 [Qemu-devel] [PATCH v9 0/2] mirror: Improve zero write and discard Fam Zheng
@ 2016-01-05 8:46 ` Fam Zheng
2016-01-06 17:53 ` Max Reitz
2016-01-06 17:57 ` Max Reitz
2016-01-05 8:46 ` [Qemu-devel] [PATCH v9 2/2] mirror: Add mirror_wait_for_io Fam Zheng
1 sibling, 2 replies; 6+ messages in thread
From: Fam Zheng @ 2016-01-05 8:46 UTC (permalink / raw)
To: qemu-devel; +Cc: Kevin Wolf, pbonzini, Jeff Cody, qemu-block, mreitz
The "pnum < nb_sectors" condition in deciding whether to actually copy
data is unnecessarily strict, and the qiov initialization is
unnecessarily for bdrv_aio_write_zeroes and bdrv_aio_discard.
Rewrite mirror_iteration to fix both flaws.
Signed-off-by: Fam Zheng <famz@redhat.com>
---
block/mirror.c | 347 +++++++++++++++++++++++++++++++++++----------------------
trace-events | 1 -
2 files changed, 216 insertions(+), 132 deletions(-)
diff --git a/block/mirror.c b/block/mirror.c
index f201f2b..e3e9fad 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -46,7 +46,6 @@ typedef struct MirrorBlockJob {
BlockdevOnError on_source_error, on_target_error;
bool synced;
bool should_complete;
- int64_t sector_num;
int64_t granularity;
size_t buf_size;
int64_t bdev_length;
@@ -63,6 +62,8 @@ typedef struct MirrorBlockJob {
int ret;
bool unmap;
bool waiting_for_io;
+ int target_cluster_sectors;
+ int max_iov;
} MirrorBlockJob;
typedef struct MirrorOp {
@@ -158,115 +159,93 @@ static void mirror_read_complete(void *opaque, int ret)
mirror_write_complete, op);
}
-static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
+/* Round sector_num and/or nb_sectors to target cluster if COW is needed, and
+ * return the offset of the adjusted tail sector against original. */
+static int mirror_cow_align(MirrorBlockJob *s,
+ int64_t *sector_num,
+ int *nb_sectors)
+{
+ bool head_need_cow, tail_need_cow;
+ int diff = 0;
+ int chunk_sectors = s->granularity >> BDRV_SECTOR_BITS;
+
+ head_need_cow = !test_bit(*sector_num / chunk_sectors, s->cow_bitmap);
+ tail_need_cow = !test_bit((*sector_num + *nb_sectors - 1) / chunk_sectors,
+ s->cow_bitmap);
+ if (head_need_cow || tail_need_cow) {
+ int64_t align_sector_num;
+ int align_nb_sectors;
+ bdrv_round_to_clusters(s->target, *sector_num, *nb_sectors,
+ &align_sector_num, &align_nb_sectors);
+ if (tail_need_cow) {
+ diff = align_sector_num + align_nb_sectors
+ - (*sector_num + *nb_sectors);
+ assert(diff >= 0);
+ *nb_sectors += diff;
+ }
+ if (head_need_cow) {
+ int d = *sector_num - align_sector_num;
+ assert(d >= 0);
+ *sector_num = align_sector_num;
+ *nb_sectors += d;
+ }
+ }
+
+ /* If the resulting chunks are more than max_iov, we have to shrink it
+ * under the alignment restriction. */
+ if (*nb_sectors > chunk_sectors * s->max_iov) {
+ int shrink = *nb_sectors - chunk_sectors * s->max_iov;
+ if (tail_need_cow) {
+ /* In this case, tail must be aligned already, so we just make sure
+ * the shrink is also aligned. */
+ shrink -= shrink % s->target_cluster_sectors;
+ }
+ assert(shrink);
+ diff -= shrink;
+ *nb_sectors -= shrink;
+ }
+
+ assert(*nb_sectors > 0);
+ return diff;
+}
+
+/* Submit async read while handling COW.
+ * Returns: nb_sectors if no alignment is necessary, or
+ * (new_end - sector_num) if tail is rounded up or down due to
+ * alignment or buffer limit.
+ */
+static int mirror_do_read(MirrorBlockJob *s, int64_t sector_num,
+ int nb_sectors)
{
BlockDriverState *source = s->common.bs;
- int nb_sectors, sectors_per_chunk, nb_chunks, max_iov;
- int64_t end, sector_num, next_chunk, next_sector, hbitmap_next_sector;
- uint64_t delay_ns = 0;
+ int sectors_per_chunk, nb_chunks;
+ int ret = nb_sectors;
MirrorOp *op;
- int pnum;
- int64_t ret;
- max_iov = MIN(source->bl.max_iov, s->target->bl.max_iov);
-
- s->sector_num = hbitmap_iter_next(&s->hbi);
- if (s->sector_num < 0) {
- bdrv_dirty_iter_init(s->dirty_bitmap, &s->hbi);
- s->sector_num = hbitmap_iter_next(&s->hbi);
- trace_mirror_restart_iter(s, bdrv_get_dirty_count(s->dirty_bitmap));
- assert(s->sector_num >= 0);
- }
-
- hbitmap_next_sector = s->sector_num;
- sector_num = s->sector_num;
sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
- end = s->bdev_length / BDRV_SECTOR_SIZE;
- /* Extend the QEMUIOVector to include all adjacent blocks that will
- * be copied in this operation.
- *
- * We have to do this if we have no backing file yet in the destination,
- * and the cluster size is very large. Then we need to do COW ourselves.
- * The first time a cluster is copied, copy it entirely. Note that,
- * because both the granularity and the cluster size are powers of two,
- * the number of sectors to copy cannot exceed one cluster.
- *
- * We also want to extend the QEMUIOVector to include more adjacent
- * dirty blocks if possible, to limit the number of I/O operations and
- * run efficiently even with a small granularity.
- */
- nb_chunks = 0;
- nb_sectors = 0;
- next_sector = sector_num;
- next_chunk = sector_num / sectors_per_chunk;
+ /* We can only handle as much as buf_size at a time. */
+ nb_sectors = MIN(s->buf_size >> BDRV_SECTOR_BITS, nb_sectors);
+ assert(nb_sectors);
- /* Wait for I/O to this cluster (from a previous iteration) to be done. */
- while (test_bit(next_chunk, s->in_flight_bitmap)) {
+ if (s->cow_bitmap) {
+ ret += mirror_cow_align(s, §or_num, &nb_sectors);
+ }
+ assert(nb_sectors << BDRV_SECTOR_BITS <= s->buf_size);
+ /* The sector range must meet granularity because:
+ * 1) Caller passes in aligned values;
+ * 2) mirror_cow_align is used only when target cluster is larger. */
+ assert(!(nb_sectors % sectors_per_chunk));
+ assert(!(sector_num % sectors_per_chunk));
+ nb_chunks = nb_sectors / sectors_per_chunk;
+
+ while (s->buf_free_count < nb_chunks) {
trace_mirror_yield_in_flight(s, sector_num, s->in_flight);
s->waiting_for_io = true;
qemu_coroutine_yield();
s->waiting_for_io = false;
}
- do {
- int added_sectors, added_chunks;
-
- if (!bdrv_get_dirty(source, s->dirty_bitmap, next_sector) ||
- test_bit(next_chunk, s->in_flight_bitmap)) {
- assert(nb_sectors > 0);
- break;
- }
-
- added_sectors = sectors_per_chunk;
- if (s->cow_bitmap && !test_bit(next_chunk, s->cow_bitmap)) {
- bdrv_round_to_clusters(s->target,
- next_sector, added_sectors,
- &next_sector, &added_sectors);
-
- /* On the first iteration, the rounding may make us copy
- * sectors before the first dirty one.
- */
- if (next_sector < sector_num) {
- assert(nb_sectors == 0);
- sector_num = next_sector;
- next_chunk = next_sector / sectors_per_chunk;
- }
- }
-
- added_sectors = MIN(added_sectors, end - (sector_num + nb_sectors));
- added_chunks = (added_sectors + sectors_per_chunk - 1) / sectors_per_chunk;
-
- /* When doing COW, it may happen that there is not enough space for
- * a full cluster. Wait if that is the case.
- */
- while (nb_chunks == 0 && s->buf_free_count < added_chunks) {
- trace_mirror_yield_buf_busy(s, nb_chunks, s->in_flight);
- s->waiting_for_io = true;
- qemu_coroutine_yield();
- s->waiting_for_io = false;
- }
- if (s->buf_free_count < nb_chunks + added_chunks) {
- trace_mirror_break_buf_busy(s, nb_chunks, s->in_flight);
- break;
- }
- if (max_iov < nb_chunks + added_chunks) {
- trace_mirror_break_iov_max(s, nb_chunks, added_chunks);
- break;
- }
-
- /* We have enough free space to copy these sectors. */
- bitmap_set(s->in_flight_bitmap, next_chunk, added_chunks);
-
- nb_sectors += added_sectors;
- nb_chunks += added_chunks;
- next_sector += added_sectors;
- next_chunk += added_chunks;
- if (!s->synced && s->common.speed) {
- delay_ns = ratelimit_calculate_delay(&s->limit, added_sectors);
- }
- } while (delay_ns == 0 && next_sector < end);
-
/* Allocate a MirrorOp that is used as an AIO callback. */
op = g_new(MirrorOp, 1);
op->s = s;
@@ -277,47 +256,152 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
* from s->buf_free.
*/
qemu_iovec_init(&op->qiov, nb_chunks);
- next_sector = sector_num;
while (nb_chunks-- > 0) {
MirrorBuffer *buf = QSIMPLEQ_FIRST(&s->buf_free);
- size_t remaining = (nb_sectors * BDRV_SECTOR_SIZE) - op->qiov.size;
+ size_t remaining = nb_sectors * BDRV_SECTOR_SIZE - op->qiov.size;
QSIMPLEQ_REMOVE_HEAD(&s->buf_free, next);
s->buf_free_count--;
qemu_iovec_add(&op->qiov, buf, MIN(s->granularity, remaining));
-
- /* Advance the HBitmapIter in parallel, so that we do not examine
- * the same sector twice.
- */
- if (next_sector > hbitmap_next_sector
- && bdrv_get_dirty(source, s->dirty_bitmap, next_sector)) {
- hbitmap_next_sector = hbitmap_iter_next(&s->hbi);
- }
-
- next_sector += sectors_per_chunk;
}
- bdrv_reset_dirty_bitmap(s->dirty_bitmap, sector_num, nb_sectors);
-
/* Copy the dirty cluster. */
s->in_flight++;
s->sectors_in_flight += nb_sectors;
trace_mirror_one_iteration(s, sector_num, nb_sectors);
- ret = bdrv_get_block_status_above(source, NULL, sector_num,
- nb_sectors, &pnum);
- if (ret < 0 || pnum < nb_sectors ||
- (ret & BDRV_BLOCK_DATA && !(ret & BDRV_BLOCK_ZERO))) {
- bdrv_aio_readv(source, sector_num, &op->qiov, nb_sectors,
- mirror_read_complete, op);
- } else if (ret & BDRV_BLOCK_ZERO) {
+ bdrv_aio_readv(source, sector_num, &op->qiov, nb_sectors,
+ mirror_read_complete, op);
+ return ret;
+}
+
+static void mirror_do_zero_or_discard(MirrorBlockJob *s,
+ int64_t sector_num,
+ int nb_sectors,
+ bool is_discard)
+{
+ MirrorOp *op;
+
+ /* Allocate a MirrorOp that is used as an AIO callback. The qiov is zeroed
+ * so the freeing in mirror_iteration_done is nop. */
+ op = g_new0(MirrorOp, 1);
+ op->s = s;
+ op->sector_num = sector_num;
+ op->nb_sectors = nb_sectors;
+
+ s->in_flight++;
+ s->sectors_in_flight += nb_sectors;
+ if (is_discard) {
+ bdrv_aio_discard(s->target, sector_num, op->nb_sectors,
+ mirror_write_complete, op);
+ } else {
bdrv_aio_write_zeroes(s->target, sector_num, op->nb_sectors,
s->unmap ? BDRV_REQ_MAY_UNMAP : 0,
mirror_write_complete, op);
- } else {
- assert(!(ret & BDRV_BLOCK_DATA));
- bdrv_aio_discard(s->target, sector_num, op->nb_sectors,
- mirror_write_complete, op);
+ }
+}
+
+static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
+{
+ BlockDriverState *source = s->common.bs;
+ int64_t sector_num;
+ uint64_t delay_ns = 0;
+ /* At least the first dirty chunk is mirrored in one iteration. */
+ int nb_chunks = 1;
+ int64_t end = s->bdev_length / BDRV_SECTOR_SIZE;
+ int sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
+
+ sector_num = hbitmap_iter_next(&s->hbi);
+ if (sector_num < 0) {
+ bdrv_dirty_iter_init(s->dirty_bitmap, &s->hbi);
+ sector_num = hbitmap_iter_next(&s->hbi);
+ trace_mirror_restart_iter(s, bdrv_get_dirty_count(s->dirty_bitmap));
+ assert(sector_num >= 0);
+ }
+
+ /* Find the number of consective dirty chunks following the first dirty
+ * one, and wait for in flight requests in them. */
+ while (nb_chunks * sectors_per_chunk < (s->buf_size >> BDRV_SECTOR_BITS)) {
+ int64_t hbitmap_next;
+ int64_t next_sector = sector_num + nb_chunks * sectors_per_chunk;
+ int64_t next_chunk = next_sector / sectors_per_chunk;
+ if (next_sector >= end ||
+ !bdrv_get_dirty(source, s->dirty_bitmap, next_sector)) {
+ break;
+ }
+ if (test_bit(next_chunk, s->in_flight_bitmap)) {
+ if (nb_chunks > 0) {
+ break;
+ }
+ trace_mirror_yield_in_flight(s, next_sector, s->in_flight);
+ s->waiting_for_io = true;
+ qemu_coroutine_yield();
+ s->waiting_for_io = false;
+ /* Now retry. */
+ } else {
+ hbitmap_next = hbitmap_iter_next(&s->hbi);
+ assert(hbitmap_next == next_sector);
+ nb_chunks++;
+ }
+ }
+
+ /* Clear dirty bits before querying the block status, because
+ * calling bdrv_get_block_status_above could yield - if some blocks are
+ * marked dirty in this window, we need to know.
+ */
+ bdrv_reset_dirty_bitmap(s->dirty_bitmap, sector_num,
+ nb_chunks * sectors_per_chunk);
+ bitmap_set(s->in_flight_bitmap, sector_num / sectors_per_chunk, nb_chunks);
+ while (nb_chunks > 0 && sector_num < end) {
+ int ret;
+ int io_sectors;
+ enum MirrorMethod {
+ MIRROR_METHOD_COPY,
+ MIRROR_METHOD_ZERO,
+ MIRROR_METHOD_DISCARD
+ } mirror_method = MIRROR_METHOD_COPY;
+
+ assert(!(sector_num % sectors_per_chunk));
+ ret = bdrv_get_block_status_above(source, NULL, sector_num,
+ nb_chunks * sectors_per_chunk,
+ &io_sectors);
+ if (ret < 0) {
+ io_sectors = nb_chunks * sectors_per_chunk;
+ }
+
+ io_sectors -= io_sectors % sectors_per_chunk;
+ if (io_sectors < sectors_per_chunk) {
+ io_sectors = sectors_per_chunk;
+ } else if (ret >= 0 && !(ret & BDRV_BLOCK_DATA)) {
+ int64_t target_sector_num;
+ int target_nb_sectors;
+ bdrv_round_to_clusters(s->target, sector_num, io_sectors,
+ &target_sector_num, &target_nb_sectors);
+ if (target_sector_num == sector_num &&
+ target_nb_sectors == io_sectors) {
+ mirror_method = ret & BDRV_BLOCK_ZERO ?
+ MIRROR_METHOD_ZERO :
+ MIRROR_METHOD_DISCARD;
+ }
+ }
+
+ switch (mirror_method) {
+ case MIRROR_METHOD_COPY:
+ io_sectors = mirror_do_read(s, sector_num, io_sectors);
+ break;
+ case MIRROR_METHOD_ZERO:
+ mirror_do_zero_or_discard(s, sector_num, io_sectors, false);
+ break;
+ case MIRROR_METHOD_DISCARD:
+ mirror_do_zero_or_discard(s, sector_num, io_sectors, true);
+ break;
+ default:
+ abort();
+ }
+ assert(io_sectors);
+ sector_num += io_sectors;
+ nb_chunks -= io_sectors / sectors_per_chunk;
+ delay_ns += ratelimit_calculate_delay(&s->limit, io_sectors);
}
return delay_ns;
}
@@ -447,16 +531,17 @@ static void coroutine_fn mirror_run(void *opaque)
*/
bdrv_get_backing_filename(s->target, backing_filename,
sizeof(backing_filename));
- if (backing_filename[0] && !s->target->backing) {
- ret = bdrv_get_info(s->target, &bdi);
- if (ret < 0) {
- goto immediate_exit;
- }
- if (s->granularity < bdi.cluster_size) {
- s->buf_size = MAX(s->buf_size, bdi.cluster_size);
- s->cow_bitmap = bitmap_new(length);
- }
+ ret = bdrv_get_info(s->target, &bdi);
+ if (ret < 0) {
+ goto immediate_exit;
}
+ if (backing_filename[0] && !s->target->backing
+ && s->granularity < bdi.cluster_size) {
+ s->buf_size = MAX(s->buf_size, bdi.cluster_size);
+ s->cow_bitmap = bitmap_new(length);
+ }
+ s->target_cluster_sectors = bdi.cluster_size >> BDRV_SECTOR_BITS;
+ s->max_iov = MIN(s->common.bs->bl.max_iov, s->target->bl.max_iov);
end = s->bdev_length / BDRV_SECTOR_SIZE;
s->buf = qemu_try_blockalign(bs, s->buf_size);
diff --git a/trace-events b/trace-events
index 6f03638..597b140 100644
--- a/trace-events
+++ b/trace-events
@@ -95,7 +95,6 @@ mirror_yield(void *s, int64_t cnt, int buf_free_count, int in_flight) "s %p dirt
mirror_yield_in_flight(void *s, int64_t sector_num, int in_flight) "s %p sector_num %"PRId64" in_flight %d"
mirror_yield_buf_busy(void *s, int nb_chunks, int in_flight) "s %p requested chunks %d in_flight %d"
mirror_break_buf_busy(void *s, int nb_chunks, int in_flight) "s %p requested chunks %d in_flight %d"
-mirror_break_iov_max(void *s, int nb_chunks, int added_chunks) "s %p requested chunks %d added_chunks %d"
# block/backup.c
backup_do_cow_enter(void *job, int64_t start, int64_t sector_num, int nb_sectors) "job %p start %"PRId64" sector_num %"PRId64" nb_sectors %d"
--
2.4.3
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