[PATCH v6 1/2] conf, docs: Add qcow2 cache configuration support

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Random write IOPS will drop dramatically if qcow2 l2 cache could not
cover the whole disk. This patch gives libvirt user a chance to adjust
the qcow2 cache configuration.

Three new qcow2 driver parameters (l2-cache-size, refcount-cache-size
and cache-clean-interval) are added as attributes to a new <qcow2>
subelement for a <driver name='qemu' type='qcow2'...> of a <disk>
element. The QEMU source docs/qcow2-cache.txt provides the guidelines
for defining/configuring values for each.

Signed-off-by: Liu Qing <liuqing@xxxxxxxxxx>
---

change since v4: removed unnecessary cache error check

 docs/formatdomain.html.in                          | 41 +++++++++
 docs/schemas/domaincommon.rng                      | 35 ++++++++
 src/conf/domain_conf.c                             | 97 ++++++++++++++++++++--
 src/qemu/qemu_driver.c                             |  5 ++
 src/util/virstoragefile.c                          |  3 +
 src/util/virstoragefile.h                          |  6 ++
 .../qemuxml2argv-disk-drive-qcow2-cache.xml        | 43 ++++++++++
 .../qemuxml2xmlout-disk-drive-qcow2-cache.xml      | 43 ++++++++++
 tests/qemuxml2xmltest.c                            |  1 +
 9 files changed, 267 insertions(+), 7 deletions(-)
 create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-disk-drive-qcow2-cache.xml
 create mode 100644 tests/qemuxml2xmloutdata/qemuxml2xmlout-disk-drive-qcow2-cache.xml

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index 8ca7637..4574e3a 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -3036,6 +3036,47 @@
           set. (<span class="since">Since 3.5.0</span>)
           </li>
         </ul>
+        The <code>driver</code> element may contain a <code>qcow2</code> sub
+        element, which to specifying further details related to a qcow2 disk.
+        For recommended setting guidelines refer to the QEMU source file
+        <code>docs/qcow2-cache.txt</code>.
+        <span class="since">Since 3.8.0</span>
+        <ul>
+          <li>
+            The optional <code>l2_cache_size</code> attribute controls how much
+            memory will be consumed by qcow2 l2 table cache in bytes. This
+            option is only valid when the driver type is qcow2. The default
+            size is 2097152.
+            <span class='since'>Since 3.8.0</span>
+
+            <b>In general you should leave this option alone, unless you
+            are very certain you know what you are doing.</b>
+          </li>
+          <li>
+            The optional <code>refcount_cache_size</code> attribute controls
+            how much memory will be consumed by qcow2 reference count table
+            cache in bytes. This option is only valid when the driver type is
+            qcow2. The default size is 262144.
+            <span class='since'>Since 3.8.0</span>
+
+            <b>In general you should leave this option alone, unless you
+            are very certain you know what you are doing.</b>
+          </li>
+          <li>
+            The optional <code>cache_clean_interval</code> attribute defines
+            an interval (in seconds). All cache entries that haven't been
+            accessed during that interval are removed from memory. This option
+            is only valid when the driver type is qcow2. The default
+            value is 0, which disables this feature. If the interval is too
+            short, it will cause frequent cache write back and load, which
+            impact performance. If the interval is too long, unused cache
+            will still consume memory until it's been written back to disk.
+            <span class='since'>Since 3.8.0</span>
+
+            <b>In general you should leave this option alone, unless you
+            are very certain you know what you are doing.</b>
+          </li>
+        </ul>
       </dd>
       <dt><code>backenddomain</code></dt>
       <dd>The optional <code>backenddomain</code> element allows specifying a
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index c9a4f7a..0e25f44 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -1756,6 +1756,23 @@
     </element>
   </define>
   <!--
+     Parameters for qcow2 driver
+    -->
+  <define name="qcow2Driver">
+    <element name="qcow2">
+      <optional>
+        <ref name="qcow2_l2_cache_size"/>
+      </optional>
+      <optional>
+        <ref name="qcow2_refcount_cache_size"/>
+      </optional>
+      <optional>
+        <ref name="qcow2_cache_clean_interval"/>
+      </optional>
+    </element>
+  </define>
+
+  <!--
       Disk may use a special driver for access.
     -->
   <define name="diskDriver">
@@ -1794,6 +1811,9 @@
         <ref name="detect_zeroes"/>
       </optional>
       <ref name="virtioOptions"/>
+      <optional>
+        <ref name="qcow2Driver"/>
+      </optional>
       <empty/>
     </element>
   </define>
@@ -1889,6 +1909,21 @@
       </choice>
     </attribute>
   </define>
+  <define name="qcow2_l2_cache_size">
+    <attribute name='l2_cache_size'>
+      <ref name="unsignedLong"/>
+    </attribute>
+  </define>
+  <define name="qcow2_refcount_cache_size">
+    <attribute name='refcount_cache_size'>
+      <ref name="unsignedLong"/>
+    </attribute>
+  </define>
+  <define name="qcow2_cache_clean_interval">
+    <attribute name='cache_clean_interval'>
+      <ref name="unsignedLong"/>
+    </attribute>
+  </define>
   <define name="controller">
     <element name="controller">
       <optional>
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index a43b25c..f225a7f 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -5734,6 +5734,30 @@ virDomainDeviceLoadparmIsValid(const char *loadparm)
 
 
 static void
+virDomainQcow2CacheOptionsFormat(virBufferPtr buf,
+                                 virDomainDiskDefPtr def)
+{
+    if (def->src->l2_cache_size == 0 &&
+        def->src->refcount_cache_size == 0 &&
+        def->src->cache_clean_interval == 0)
+        return;
+
+    virBufferAddLit(buf, "<qcow2");
+
+    if (def->src->l2_cache_size > 0)
+        virBufferAsprintf(buf, " l2_cache_size='%llu'",
+                          def->src->l2_cache_size);
+    if (def->src->refcount_cache_size > 0)
+        virBufferAsprintf(buf, " refcount_cache_size='%llu'",
+                          def->src->refcount_cache_size);
+    if (def->src->cache_clean_interval > 0)
+        virBufferAsprintf(buf, " cache_clean_interval='%llu'",
+                          def->src->cache_clean_interval);
+    virBufferAddLit(buf, "/>\n");
+}
+
+
+static void
 virDomainVirtioOptionsFormat(virBufferPtr buf,
                              virDomainVirtioOptionsPtr virtio)
 {
@@ -8572,15 +8596,69 @@ virDomainDiskDefParseValidate(const virDomainDiskDef *def)
         }
     }
 
+    if (def->src->format != VIR_STORAGE_FILE_QCOW2 &&
+        (def->src->l2_cache_size > 0 || def->src->refcount_cache_size > 0 ||
+         def->src->cache_clean_interval > 0)) {
+        virReportError(VIR_ERR_XML_ERROR,
+                       _("Setting l2_cache_size, refcount_cache_size, "
+                         "cache_clean_interval is not allowed for types "
+                         "other than QCOW2"));
+        return -1;
+    }
+
     return 0;
 }
 
 
 static int
+virDomainDiskDefQcow2ParseXML(virDomainDiskDefPtr def,
+                              xmlNodePtr cur)
+{
+    char *tmp = NULL;
+    int ret = -1;
+
+    if ((tmp = virXMLPropString(cur, "l2_cache_size")) &&
+        (virStrToLong_ullp(tmp, NULL, 10, &def->src->l2_cache_size) < 0)) {
+        virReportError(VIR_ERR_XML_ERROR,
+                       _("Invalid l2_cache_size attribute in disk "
+                         "driver element: %s"), tmp);
+        goto cleanup;
+    }
+    VIR_FREE(tmp);
+
+    if ((tmp = virXMLPropString(cur, "refcount_cache_size")) &&
+        (virStrToLong_ullp(tmp, NULL, 10, &def->src->refcount_cache_size) < 0)) {
+        virReportError(VIR_ERR_XML_ERROR,
+                       _("Invalid refcount_cache_size attribute in disk "
+                         "driver element: %s"), tmp);
+        goto cleanup;
+    }
+    VIR_FREE(tmp);
+
+    if ((tmp = virXMLPropString(cur, "cache_clean_interval")) &&
+        (virStrToLong_ullp(tmp, NULL, 10, &def->src->cache_clean_interval) < 0)) {
+        virReportError(VIR_ERR_XML_ERROR,
+                       _("Invalid cache_clean_interval attribute in "
+                         "disk driver element: %s"), tmp);
+        goto cleanup;
+    }
+    VIR_FREE(tmp);
+
+    ret = 0;
+
+ cleanup:
+    VIR_FREE(tmp);
+
+    return ret;
+}
+
+
+static int
 virDomainDiskDefDriverParseXML(virDomainDiskDefPtr def,
                                xmlNodePtr cur)
 {
     char *tmp = NULL;
+    xmlNodePtr child;
     int ret = -1;
 
     def->src->driverName = virXMLPropString(cur, "name");
@@ -8683,6 +8761,13 @@ virDomainDiskDefDriverParseXML(virDomainDiskDefPtr def,
     }
     VIR_FREE(tmp);
 
+    for (child = cur->children; child != NULL; child = child->next) {
+        if (virXMLNodeNameEqual(child, "qcow2") &&
+            virDomainDiskDefQcow2ParseXML(def, child) < 0) {
+            goto cleanup;
+        }
+    }
+
     ret = 0;
 
  cleanup:
@@ -21885,6 +21970,7 @@ virDomainDiskDefFormat(virBufferPtr buf,
     const char *discard = virDomainDiskDiscardTypeToString(def->discard);
     const char *detect_zeroes = virDomainDiskDetectZeroesTypeToString(def->detect_zeroes);
     virBuffer driverBuf = VIR_BUFFER_INITIALIZER;
+    virBuffer driverQcow2Buf = VIR_BUFFER_INITIALIZER;
 
     if (!type || !def->src->type) {
         virReportError(VIR_ERR_INTERNAL_ERROR,
@@ -21963,14 +22049,11 @@ virDomainDiskDefFormat(virBufferPtr buf,
 
     virDomainVirtioOptionsFormat(&driverBuf, def->virtio);
 
-    if (virBufferCheckError(&driverBuf) < 0)
-        return -1;
+    virBufferSetChildIndent(&driverQcow2Buf, buf);
+    virDomainQcow2CacheOptionsFormat(&driverQcow2Buf, def);
 
-    if (virBufferUse(&driverBuf)) {
-        virBufferAddLit(buf, "<driver");
-        virBufferAddBuffer(buf, &driverBuf);
-        virBufferAddLit(buf, "/>\n");
-    }
+    if (virXMLFormatElement(buf, "driver", &driverBuf, &driverQcow2Buf) < 0)
+        return -1;
 
     if (def->src->auth) {
         if (virStorageAuthDefFormat(buf, def->src->auth) < 0)
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index e956839..c3b81e1 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -14318,6 +14318,11 @@ qemuDomainSnapshotDiskDataCollect(virQEMUDriverPtr driver,
         if (!(dd->src = virStorageSourceCopy(snap->def->disks[i].src, false)))
             goto error;
 
+        /* keep the qcow2 cache configuration */
+        dd->src->l2_cache_size = vm->def->disks[i]->src->l2_cache_size;
+        dd->src->refcount_cache_size = vm->def->disks[i]->src->refcount_cache_size;
+        dd->src->cache_clean_interval = vm->def->disks[i]->src->cache_clean_interval;
+
         if (virStorageSourceInitChainElement(dd->src, dd->disk->src, false) < 0)
             goto error;
 
diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c
index e94ad32..f23390f 100644
--- a/src/util/virstoragefile.c
+++ b/src/util/virstoragefile.c
@@ -2038,6 +2038,9 @@ virStorageSourceCopy(const virStorageSource *src,
     ret->physical = src->physical;
     ret->readonly = src->readonly;
     ret->shared = src->shared;
+    ret->l2_cache_size = src->l2_cache_size;
+    ret->refcount_cache_size = src->refcount_cache_size;
+    ret->cache_clean_interval = src->cache_clean_interval;
 
     /* storage driver metadata are not copied */
     ret->drv = NULL;
diff --git a/src/util/virstoragefile.h b/src/util/virstoragefile.h
index 6c388b1..9b5a5f3 100644
--- a/src/util/virstoragefile.h
+++ b/src/util/virstoragefile.h
@@ -280,6 +280,12 @@ struct _virStorageSource {
     /* metadata that allows identifying given storage source */
     char *nodeformat;  /* name of the format handler object */
     char *nodestorage; /* name of the storage object */
+
+    unsigned long long l2_cache_size; /* qcow2 l2 cache size */
+    /* qcow2 reference count table cache size */
+    unsigned long long refcount_cache_size;
+    /* clean unused cache entries interval */
+    unsigned long long cache_clean_interval;
 };
 
 
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-disk-drive-qcow2-cache.xml b/tests/qemuxml2argvdata/qemuxml2argv-disk-drive-qcow2-cache.xml
new file mode 100644
index 0000000..3f464db
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-disk-drive-qcow2-cache.xml
@@ -0,0 +1,43 @@
+<domain type='qemu'>
+  <name>QEMUGuest1</name>
+  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>219136</memory>
+  <currentMemory unit='KiB'>219136</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-i686</emulator>
+    <disk type='block' device='disk'>
+      <driver name='qemu' type='qcow2' cache='none'>
+        <qcow2 l2_cache_size='2097152' refcount_cache_size='524288' cache_clean_interval='900'/>
+      </driver>
+      <source dev='/dev/HostVG/QEMUGuest1'/>
+      <target dev='hda' bus='ide'/>
+      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
+    </disk>
+    <disk type='block' device='cdrom'>
+      <driver name='qemu' type='raw'/>
+      <source dev='/dev/HostVG/QEMUGuest2'/>
+      <target dev='hdc' bus='ide'/>
+      <readonly/>
+      <address type='drive' controller='0' bus='1' target='0' unit='0'/>
+    </disk>
+    <controller type='usb' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
+    </controller>
+    <controller type='ide' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
+    </controller>
+    <controller type='pci' index='0' model='pci-root'/>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='none'/>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2xmloutdata/qemuxml2xmlout-disk-drive-qcow2-cache.xml b/tests/qemuxml2xmloutdata/qemuxml2xmlout-disk-drive-qcow2-cache.xml
new file mode 100644
index 0000000..3f464db
--- /dev/null
+++ b/tests/qemuxml2xmloutdata/qemuxml2xmlout-disk-drive-qcow2-cache.xml
@@ -0,0 +1,43 @@
+<domain type='qemu'>
+  <name>QEMUGuest1</name>
+  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>219136</memory>
+  <currentMemory unit='KiB'>219136</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-i686</emulator>
+    <disk type='block' device='disk'>
+      <driver name='qemu' type='qcow2' cache='none'>
+        <qcow2 l2_cache_size='2097152' refcount_cache_size='524288' cache_clean_interval='900'/>
+      </driver>
+      <source dev='/dev/HostVG/QEMUGuest1'/>
+      <target dev='hda' bus='ide'/>
+      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
+    </disk>
+    <disk type='block' device='cdrom'>
+      <driver name='qemu' type='raw'/>
+      <source dev='/dev/HostVG/QEMUGuest2'/>
+      <target dev='hdc' bus='ide'/>
+      <readonly/>
+      <address type='drive' controller='0' bus='1' target='0' unit='0'/>
+    </disk>
+    <controller type='usb' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
+    </controller>
+    <controller type='ide' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
+    </controller>
+    <controller type='pci' index='0' model='pci-root'/>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='none'/>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2xmltest.c b/tests/qemuxml2xmltest.c
index 0a87ced..fab1e19 100644
--- a/tests/qemuxml2xmltest.c
+++ b/tests/qemuxml2xmltest.c
@@ -461,6 +461,7 @@ mymain(void)
     DO_TEST("disk-drive-cache-v2-none", NONE);
     DO_TEST("disk-drive-cache-directsync", NONE);
     DO_TEST("disk-drive-cache-unsafe", NONE);
+    DO_TEST("disk-drive-qcow2-cache", NONE);
     DO_TEST("disk-drive-network-nbd", NONE);
     DO_TEST("disk-drive-network-nbd-export", NONE);
     DO_TEST("disk-drive-network-nbd-ipv6", NONE);
-- 
1.8.3.1

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