[Qemu-devel] [PATCH] Collecting block device statistics

[Richard W.M. Jones]

Hi,

I was looking for a way to collect information on the amount of data 
being written and read from block devices.  The attached patch adds a 
few counters to the BlockDriverState structure to collect this 
information, and a new "info blockstats" monitor command to display it.

This screenshot shows it in action:

http://www.annexia.org/tmp/Screenshot-QEMU.png

This is the sort of feature I'd really like to see merged into qemu 
because it will let us enhance libvirt to centrally collect these stats 
from qemu instances.

Any comments or feedback about this are most welcome.

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

Index: block.c
===================================================================
RCS file: /sources/qemu/qemu/block.c,v
retrieving revision 1.47
diff -u -r1.47 block.c
--- block.c     11 Nov 2007 02:51:16 -0000      1.47
+++ block.c     16 Nov 2007 15:23:44 -0000
@@ -522,8 +522,12 @@
             return ret;
         else if (ret != len)
             return -EINVAL;
-        else
+        else {
+           bs->rd_bytes += (unsigned) len;
+           bs->rd_sects += (unsigned) nb_sectors;
+           bs->rd_ops ++;
             return 0;
+       }
     } else {
         return drv->bdrv_read(bs, sector_num, buf, nb_sectors);
     }
@@ -554,8 +558,12 @@
             return ret;
         else if (ret != len)
             return -EIO;
-        else
+        else {
+           bs->wr_bytes += (unsigned) len;
+           bs->wr_sects += (unsigned) nb_sectors;
+           bs->wr_ops ++;
             return 0;
+       }
     } else {
         return drv->bdrv_write(bs, sector_num, buf, nb_sectors);
     }
@@ -903,6 +911,27 @@
         term_printf("\n");
     }
 }
+
+/* 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(sectors)=%" PRIu64
+                    " wr(sectors)=%" PRIu64
+                    " rd(operations)=%" PRIu64
+                    " wr(operations)=%" PRIu64
+                    "\n",
+                    bs->device_name,
+                    bs->rd_bytes, bs->wr_bytes,
+                    bs->rd_sects, bs->wr_sects,
+                    bs->rd_ops, bs->wr_ops);
+    }
+}
 #endif
 
 void bdrv_get_backing_filename(BlockDriverState *bs,
@@ -1065,6 +1094,7 @@
                                 BlockDriverCompletionFunc *cb, void *opaque)
 {
     BlockDriver *drv = bs->drv;
+    BlockDriverAIOCB *ret;
 
     if (!drv)
         return NULL;
@@ -1077,7 +1107,16 @@
         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_sects += (unsigned) nb_sectors;
+       bs->rd_ops ++;
+    }
+
+    return ret;
 }
 
 BlockDriverAIOCB *bdrv_aio_write(BlockDriverState *bs, int64_t sector_num,
@@ -1085,6 +1124,7 @@
                                  BlockDriverCompletionFunc *cb, void *opaque)
 {
     BlockDriver *drv = bs->drv;
+    BlockDriverAIOCB *ret;
 
     if (!drv)
         return NULL;
@@ -1094,7 +1134,16 @@
         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_sects += (unsigned) nb_sectors;
+       bs->wr_ops ++;
+    }
+
+    return ret;
 }
 
 void bdrv_aio_cancel(BlockDriverAIOCB *acb)
Index: block.h
===================================================================
RCS file: /sources/qemu/qemu/block.h,v
retrieving revision 1.1
diff -u -r1.1 block.h
--- block.h     11 Nov 2007 02:51:16 -0000      1.1
+++ block.h     16 Nov 2007 15:23:44 -0000
@@ -48,6 +48,7 @@
 
 #ifndef QEMU_IMG
 void bdrv_info(void);
+void bdrv_info_stats(void);
 #endif
 
 void bdrv_init(void);
Index: block_int.h
===================================================================
RCS file: /sources/qemu/qemu/block_int.h,v
retrieving revision 1.14
diff -u -r1.14 block_int.h
--- block_int.h 11 Nov 2007 02:51:16 -0000      1.14
+++ block_int.h 16 Nov 2007 15:23:44 -0000
@@ -114,6 +114,14 @@
 
     void *sync_aiocb;
 
+    /* I/O stats (display with "info blockstats"). */
+    uint64_t rd_bytes;
+    uint64_t wr_bytes;
+    uint64_t rd_sects;
+    uint64_t wr_sects;
+    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;
Index: monitor.c
===================================================================
RCS file: /sources/qemu/qemu/monitor.c,v
retrieving revision 1.85
diff -u -r1.85 monitor.c
--- monitor.c   26 Oct 2007 18:42:57 -0000      1.85
+++ monitor.c   16 Nov 2007 15:23:46 -0000
@@ -249,6 +249,11 @@
     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)
 {
@@ -1321,6 +1326,8 @@
       "", "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,

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