[Qemu-block] [RFC PATCH V2] qemu-img: make convert async

[Peter Lieven]

this is something I have been thinking about for almost 2 years now.
we heavily have the following two use cases when using qemu-img convert.

a) reading from NFS and writing to iSCSI for deploying templates
b) reading from iSCSI and writing to NFS for backups

In both processes we use libiscsi and libnfs so we have no kernel pagecache.
As qemu-img convert is implemented with sync operations that means we
read one buffer and then write it. No parallelism and each sync request
takes as long as it takes until it is completed.

This is version 2 of the approach using coroutine worker "threads".

The code is far from clean or complete, but I would appreaciate comments
and thoughts from you.

So far I have the following runtimes when reading an uncompressed QCOW2 from
NFS and writing it to iSCSI (raw):

qemu-img (master)
 nfs -> iscsi 33 secs
 nfs -> ram   19 secs
 ram -> iscsi 14 secs

qemu-img-async
 nfs -> iscsi 23 secs
 nfs -> ram   17 secs
 ram -> iscsi 14 secs

Its visible that on master the runtimes add up as expected. The async branch
is faster, but not as fast as I would have expected. I would expect the runtime
to be as slow as the slowest of the two involved transfers.

Thank you,
Peter

Signed-off-by: Peter Lieven <address@hidden>
---
v1->v2: - using coroutine as worker "threads". [Max]
        - keeping the request queue as otherwise it happens
          that we wait on BLK_ZERO chunks while keeping the write order.
          it also avoids redundant calls to get_block_status and helps
          to skip some conditions for fully allocated imaged (!s->min_sparse)

 qemu-img.c | 187 ++++++++++++++++++++++++++++++++++++++++---------------------
 1 file changed, 123 insertions(+), 64 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index cff22e3..e623188 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1448,6 +1448,16 @@ enum ImgConvertBlockStatus {
     BLK_BACKING_FILE,
 };
 
+typedef struct ImgConvertQueueElt {
+    int64_t sector_num;
+    enum ImgConvertBlockStatus status;
+    int nb_sectors;
+    QSIMPLEQ_ENTRY(ImgConvertQueueElt) next;
+} ImgConvertQueueElt;
+
+//XXX: this should be a cmdline parameter
+#define NUM_COROUTINES 8
+
 typedef struct ImgConvertState {
     BlockBackend **src;
     int64_t *src_sectors;
@@ -1455,6 +1465,8 @@ typedef struct ImgConvertState {
     int64_t src_cur_offset;
     int64_t total_sectors;
     int64_t allocated_sectors;
+    int64_t allocated_done;
+    int64_t wr_offs;
     enum ImgConvertBlockStatus status;
     int64_t sector_next_status;
     BlockBackend *target;
@@ -1464,11 +1476,16 @@ typedef struct ImgConvertState {
     int min_sparse;
     size_t cluster_sectors;
     size_t buf_sectors;
+    bool locked;
+    int ret;
+    Coroutine *co[NUM_COROUTINES];
+    QSIMPLEQ_HEAD(, ImgConvertQueueElt) queue;
 } ImgConvertState;
 
 static void convert_select_part(ImgConvertState *s, int64_t sector_num)
 {
-    assert(sector_num >= s->src_cur_offset);
+    s->src_cur_offset = 0;
+    s->src_cur = 0;
     while (sector_num - s->src_cur_offset >= s->src_sectors[s->src_cur]) {
         s->src_cur_offset += s->src_sectors[s->src_cur];
         s->src_cur++;
@@ -1545,7 +1562,7 @@ static int convert_iteration_sectors(ImgConvertState *s, 
int64_t sector_num)
 }
 
 static int convert_read(ImgConvertState *s, int64_t sector_num, int nb_sectors,
-                        uint8_t *buf)
+                        uint8_t *buf, QEMUIOVector *qiov)
 {
     int n;
     int ret;
@@ -1562,10 +1579,12 @@ static int convert_read(ImgConvertState *s, int64_t 
sector_num, int nb_sectors,
         blk = s->src[s->src_cur];
         bs_sectors = s->src_sectors[s->src_cur];
 
+        qemu_iovec_reset(qiov);
         n = MIN(nb_sectors, bs_sectors - (sector_num - s->src_cur_offset));
-        ret = blk_pread(blk,
-                        (sector_num - s->src_cur_offset) << BDRV_SECTOR_BITS,
-                        buf, n << BDRV_SECTOR_BITS);
+        qemu_iovec_add(qiov, buf, n << BDRV_SECTOR_BITS);
+
+        ret = blk_co_preadv(blk, (sector_num - s->src_cur_offset) << 
BDRV_SECTOR_BITS,
+                            n << BDRV_SECTOR_BITS, qiov, 0);
         if (ret < 0) {
             return ret;
         }
@@ -1578,15 +1597,17 @@ static int convert_read(ImgConvertState *s, int64_t 
sector_num, int nb_sectors,
     return 0;
 }
 
+
 static int convert_write(ImgConvertState *s, int64_t sector_num, int 
nb_sectors,
-                         const uint8_t *buf)
+                         uint8_t *buf, QEMUIOVector *qiov,
+                         enum ImgConvertBlockStatus status)
 {
     int ret;
 
     while (nb_sectors > 0) {
         int n = nb_sectors;
-
-        switch (s->status) {
+        qemu_iovec_reset(qiov);
+        switch (status) {
         case BLK_BACKING_FILE:
             /* If we have a backing file, leave clusters unallocated that are
              * unallocated in the source image, so that the backing file is
@@ -1607,9 +1628,9 @@ static int convert_write(ImgConvertState *s, int64_t 
sector_num, int nb_sectors,
                     break;
                 }
 
-                ret = blk_pwrite_compressed(s->target,
-                                            sector_num << BDRV_SECTOR_BITS,
-                                            buf, n << BDRV_SECTOR_BITS);
+                qemu_iovec_add(qiov, buf, n << BDRV_SECTOR_BITS);
+                ret = blk_co_pwritev(s->target, sector_num << BDRV_SECTOR_BITS,
+                                     n << BDRV_SECTOR_BITS, qiov, 
BDRV_REQ_WRITE_COMPRESSED);
                 if (ret < 0) {
                     return ret;
                 }
@@ -1622,8 +1643,9 @@ static int convert_write(ImgConvertState *s, int64_t 
sector_num, int nb_sectors,
             if (!s->min_sparse ||
                 is_allocated_sectors_min(buf, n, &n, s->min_sparse))
             {
-                ret = blk_pwrite(s->target, sector_num << BDRV_SECTOR_BITS,
-                                 buf, n << BDRV_SECTOR_BITS, 0);
+                qemu_iovec_add(qiov, buf, n << BDRV_SECTOR_BITS);
+                ret = blk_co_pwritev(s->target, sector_num << BDRV_SECTOR_BITS,
+                                     n << BDRV_SECTOR_BITS, qiov, 0);
                 if (ret < 0) {
                     return ret;
                 }
@@ -1635,8 +1657,8 @@ static int convert_write(ImgConvertState *s, int64_t 
sector_num, int nb_sectors,
             if (s->has_zero_init) {
                 break;
             }
-            ret = blk_pwrite_zeroes(s->target, sector_num << BDRV_SECTOR_BITS,
-                                    n << BDRV_SECTOR_BITS, 0);
+            ret = blk_co_pwrite_zeroes(s->target, sector_num << 
BDRV_SECTOR_BITS,
+                                       n << BDRV_SECTOR_BITS, 0);
             if (ret < 0) {
                 return ret;
             }
@@ -1651,12 +1673,75 @@ static int convert_write(ImgConvertState *s, int64_t 
sector_num, int nb_sectors,
     return 0;
 }
 
-static int convert_do_copy(ImgConvertState *s)
+static void convert_do_copy_co(void *opaque)
 {
+    ImgConvertState *s = opaque;
     uint8_t *buf = NULL;
-    int64_t sector_num, allocated_done;
+    int ret, i;
+    int64_t next_sector;
+    ImgConvertQueueElt *elt, *elt2;
+    QEMUIOVector qiov;
+    qemu_iovec_init(&qiov, 1);
+
+    buf = blk_blockalign(s->target, s->buf_sectors * BDRV_SECTOR_SIZE);
+
+    while (!s->ret && (elt = QSIMPLEQ_FIRST(&s->queue))) {
+        QSIMPLEQ_REMOVE_HEAD(&s->queue, next);
+        if ((elt2 = QSIMPLEQ_FIRST(&s->queue))) {
+            next_sector = elt2->sector_num;
+        } else {
+            next_sector = s->total_sectors;
+        }
+
+        s->allocated_done += elt->nb_sectors;
+        qemu_progress_print(100.0 * s->allocated_done / s->allocated_sectors,
+                            0);
+
+        if (elt->status == BLK_DATA) {
+            ret = convert_read(s, elt->sector_num, elt->nb_sectors, buf, 
&qiov);
+            if (ret < 0) {
+                error_report("error while reading sector %" PRId64
+                             ": %s", elt->sector_num, strerror(-ret));
+                s->ret = ret;
+                goto out;
+            }
+        }
+
+        //~ //XXX: in-order write on/off could be a switch
+        while (s->wr_offs != elt->sector_num) {
+            if (s->ret) {
+                goto out;
+            }
+            qemu_coroutine_yield();
+        }
+
+        ret = convert_write(s, elt->sector_num, elt->nb_sectors, buf, &qiov, 
elt->status);
+        if (ret < 0) {
+            error_report("error while writing sector %" PRId64
+                         ": %s", elt->sector_num, strerror(-ret));
+            s->ret = ret;
+            goto out;
+        }
+
+        s->wr_offs = next_sector;
+        g_free(elt);
+    }
+
+out:
+    qemu_iovec_destroy(&qiov);
+    qemu_vfree(buf);
+    for (i = 0; i < NUM_COROUTINES; i++) {
+        if (s->co[i] == qemu_coroutine_self()) {
+            s->co[i] = NULL;
+        }
+    }
+}
+
+static int convert_do_copy(ImgConvertState *s)
+{
     int ret;
-    int n;
+    int i, n, running = -1;
+    int64_t sector_num = 0;
 
     /* Check whether we have zero initialisation or can get it efficiently */
     s->has_zero_init = s->min_sparse && !s->target_has_backing
@@ -1682,69 +1767,44 @@ static int convert_do_copy(ImgConvertState *s)
         }
         s->buf_sectors = s->cluster_sectors;
     }
-    buf = blk_blockalign(s->target, s->buf_sectors * BDRV_SECTOR_SIZE);
 
-    /* Calculate allocated sectors for progress */
-    s->allocated_sectors = 0;
-    sector_num = 0;
+    QSIMPLEQ_INIT(&s->queue);
     while (sector_num < s->total_sectors) {
         n = convert_iteration_sectors(s, sector_num);
         if (n < 0) {
             ret = n;
             goto fail;
         }
+
         if (s->status == BLK_DATA || (!s->min_sparse && s->status == BLK_ZERO))
         {
+            ImgConvertQueueElt *elt = g_malloc(sizeof(ImgConvertQueueElt));
+            elt->sector_num = sector_num;
+            elt->status = s->status;
+            elt->nb_sectors = n;
             s->allocated_sectors += n;
+            QSIMPLEQ_INSERT_TAIL(&s->queue, elt, next);
         }
         sector_num += n;
     }
 
-    /* Do the copy */
-    s->src_cur = 0;
-    s->src_cur_offset = 0;
-    s->sector_next_status = 0;
-
-    sector_num = 0;
-    allocated_done = 0;
-
-    while (sector_num < s->total_sectors) {
-        n = convert_iteration_sectors(s, sector_num);
-        if (n < 0) {
-            ret = n;
-            goto fail;
-        }
-        if (s->status == BLK_DATA || (!s->min_sparse && s->status == BLK_ZERO))
-        {
-            allocated_done += n;
-            qemu_progress_print(100.0 * allocated_done / s->allocated_sectors,
-                                0);
-        }
+    for (i = 0; i < NUM_COROUTINES; i++) {
+        s->co[i] = qemu_coroutine_create(convert_do_copy_co, s);
+        qemu_coroutine_enter(s->co[i]);
+    }
 
-        if (s->status == BLK_DATA) {
-            ret = convert_read(s, sector_num, n, buf);
-            if (ret < 0) {
-                error_report("error while reading sector %" PRId64
-                             ": %s", sector_num, strerror(-ret));
-                goto fail;
+    while (!s->ret && running) {
+        running = 0;
+        for (i = 0; i < NUM_COROUTINES; i++) {
+            if (s->co[i] != NULL) {
+                qemu_coroutine_enter_if_inactive(s->co[i]);
+                running++;
             }
-        } else if (!s->min_sparse && s->status == BLK_ZERO) {
-            n = MIN(n, s->buf_sectors);
-            memset(buf, 0, n * BDRV_SECTOR_SIZE);
-            s->status = BLK_DATA;
-        }
-
-        ret = convert_write(s, sector_num, n, buf);
-        if (ret < 0) {
-            error_report("error while writing sector %" PRId64
-                         ": %s", sector_num, strerror(-ret));
-            goto fail;
         }
-
-        sector_num += n;
+        main_loop_wait(false);
     }
 
-    if (s->compressed) {
+    if (s->compressed && !s->ret) {
         /* signal EOF to align */
         ret = blk_pwrite_compressed(s->target, 0, NULL, 0);
         if (ret < 0) {
@@ -1752,9 +1812,8 @@ static int convert_do_copy(ImgConvertState *s)
         }
     }
 
-    ret = 0;
+    ret = s->ret;
 fail:
-    qemu_vfree(buf);
     return ret;
 }
 
-- 
1.9.1