'info blockstats' to collect block device statistics

["Richard W.M. Jones" <rjones-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

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I wonder if KVM would be interested in taking my QEMU patch to support 
block device statistics.

This patch collects per-block-device statistics and allows them to be 
displayed in the monitor through a 'info blockstats' command. It 
generalises the VMDK-only support for this which was added to KVM's 
version of QEMU.

Proposed patch:
http://lists.gnu.org/archive/html/qemu-devel/2007-11/msg00770.html

Accepted into QEMU:
http://lists.gnu.org/archive/html/qemu-devel/2007-12/msg00013.html

The QEMU patch doesn't quite apply directly because KVM has no file 
qemu/block.h.  Attached is a rebased patch against the current 
kvm-userspace.

Rich.

-- 
Emerging Technologies, Red Hat - http://et.redhat.com/~rjones/
Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod
Street, Windsor, Berkshire, SL4 1TE, United Kingdom.  Registered in
England and Wales under Company Registration No. 03798903

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diff --git a/qemu/block.c b/qemu/block.c
index 20d2e1c..20296c5 100644
--- a/qemu/block.c
+++ b/qemu/block.c
@@ -518,8 +518,11 @@ int bdrv_read(BlockDriverState *bs, int64_t sector_num,
             return ret;
         else if (ret != len)
             return -EINVAL;
-        else
+        else {
+	    bs->rd_bytes += (unsigned) len;
+	    bs->rd_ops ++;
             return 0;
+	}
     } else {
         return drv->bdrv_read(bs, sector_num, buf, nb_sectors);
     }
@@ -550,8 +553,11 @@ int bdrv_write(BlockDriverState *bs, int64_t sector_num,
             return ret;
         else if (ret != len)
             return -EIO;
-        else
+        else {
+	    bs->wr_bytes += (unsigned) len;
+	    bs->wr_ops ++;
             return 0;
+	}
     } else {
         return drv->bdrv_write(bs, sector_num, buf, nb_sectors);
     }
@@ -914,6 +920,25 @@ void bdrv_info(void)
     }
 }
 
+/* The "info blockstats" command. */
+void bdrv_info_stats (void)
+{
+    BlockDriverState *bs;
+
+    for (bs = bdrv_first; bs != NULL; bs = bs->next) {
+      term_printf ("%s:"
+                   " rd_bytes=%" PRIu64
+                   " wr_bytes=%" PRIu64
+                   " rd_operations=%" PRIu64
+                   " wr_operations=%" PRIu64
+                   "\n",
+                   bs->device_name,
+                   bs->rd_bytes, bs->wr_bytes,
+                   bs->rd_ops, bs->wr_ops);
+    }
+}
+
+
 void bdrv_get_backing_filename(BlockDriverState *bs,
                                char *filename, int filename_size)
 {
@@ -1074,6 +1099,7 @@ BlockDriverAIOCB *bdrv_aio_read(BlockDriverState *bs, int64_t sector_num,
                                 BlockDriverCompletionFunc *cb, void *opaque)
 {
     BlockDriver *drv = bs->drv;
+    BlockDriverAIOCB *ret;
 
     if (!drv)
         return NULL;
@@ -1086,7 +1112,15 @@ BlockDriverAIOCB *bdrv_aio_read(BlockDriverState *bs, int64_t sector_num,
         buf += 512;
     }
 
-    return drv->bdrv_aio_read(bs, sector_num, buf, nb_sectors, cb, opaque);
+    ret = drv->bdrv_aio_read(bs, sector_num, buf, nb_sectors, cb, opaque);
+
+    if (ret) {
+	/* Update stats even though technically transfer has not happened. */
+	bs->rd_bytes += (unsigned) nb_sectors * SECTOR_SIZE;
+	bs->rd_ops ++;
+    }
+
+    return ret;
 }
 
 BlockDriverAIOCB *bdrv_aio_write(BlockDriverState *bs, int64_t sector_num,
@@ -1094,6 +1128,7 @@ BlockDriverAIOCB *bdrv_aio_write(BlockDriverState *bs, int64_t sector_num,
                                  BlockDriverCompletionFunc *cb, void *opaque)
 {
     BlockDriver *drv = bs->drv;
+    BlockDriverAIOCB *ret;
 
     if (!drv)
         return NULL;
@@ -1103,7 +1138,15 @@ BlockDriverAIOCB *bdrv_aio_write(BlockDriverState *bs, int64_t sector_num,
         memcpy(bs->boot_sector_data, buf, 512);
     }
 
-    return drv->bdrv_aio_write(bs, sector_num, buf, nb_sectors, cb, opaque);
+    ret = drv->bdrv_aio_write(bs, sector_num, buf, nb_sectors, cb, opaque);
+
+    if (ret) {
+	/* Update stats even though technically transfer has not happened. */
+	bs->wr_bytes += (unsigned) nb_sectors * SECTOR_SIZE;
+	bs->wr_ops ++;
+    }
+
+    return ret;
 }
 
 void bdrv_aio_cancel(BlockDriverAIOCB *acb)
diff --git a/qemu/block_int.h b/qemu/block_int.h
index b034023..d3f9fda 100644
--- a/qemu/block_int.h
+++ b/qemu/block_int.h
@@ -112,6 +112,12 @@ struct BlockDriverState {
 
     void *sync_aiocb;
 
+    /* I/O stats (display with "info blockstats"). */
+    uint64_t rd_bytes;
+    uint64_t wr_bytes;
+    uint64_t rd_ops;
+    uint64_t wr_ops;
+
     /* NOTE: the following infos are only hints for real hardware
        drivers. They are not used by the block driver */
     int cyls, heads, secs, translation;
diff --git a/qemu/monitor.c b/qemu/monitor.c
index 10e0af9..a7f4490 100644
--- a/qemu/monitor.c
+++ b/qemu/monitor.c
@@ -251,6 +251,11 @@ static void do_info_block(void)
     bdrv_info();
 }
 
+static void do_info_blockstats(void)
+{
+    bdrv_info_stats();
+}
+
 /* get the current CPU defined by the user */
 int mon_set_cpu(int cpu_index)
 {
@@ -1389,6 +1394,8 @@ static term_cmd_t info_cmds[] = {
       "", "show the network state" },
     { "block", "", do_info_block,
       "", "show the block devices" },
+    { "blockstats", "", do_info_blockstats,
+      "", "show block device statistics" },
     { "registers", "", do_info_registers,
       "", "show the cpu registers" },
     { "cpus", "", do_info_cpus,
diff --git a/qemu/vl.h b/qemu/vl.h
index 01aeabc..c07a104 100644
--- a/qemu/vl.h
+++ b/qemu/vl.h
@@ -729,6 +729,7 @@ void bdrv_set_change_cb(BlockDriverState *bs,
                         void (*change_cb)(void *opaque), void *opaque);
 void bdrv_get_format(BlockDriverState *bs, char *buf, int buf_size);
 void bdrv_info(void);
+void bdrv_info_stats(void);
 BlockDriverState *bdrv_find(const char *name);
 void bdrv_iterate(void (*it)(void *opaque, const char *name), void *opaque);
 int bdrv_is_encrypted(BlockDriverState *bs);

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