[PATCH] qemu: virtiofs: Add pool element to limit thread pool

[Masayoshi Mizuma <msys.mizuma@xxxxxxxxx>]

From: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>

virtiofsd has --thread-pool-size=NUM option to limit the
thread pool size. It will be useful to tune the performance.

Add pool element to use the option like as:

   <filesystem type='mount' accessmode='passthrough'>
       <driver type='virtiofs' queue='1024'/>
       <binary path='/usr/libexec/virtiofsd' xattr='on' pool='32'/>
       <source dir='/path'/>
       <target dir='mount_tag'/>
   </filesystem>

Signed-off-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>
---
 docs/formatdomain.rst         |  6 ++++--
 docs/schemas/domaincommon.rng |  5 +++++
 src/conf/domain_conf.c        | 12 ++++++++++++
 src/conf/domain_conf.h        |  1 +
 src/qemu/qemu_virtiofs.c      |  3 +++
 5 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index bfa80e4bc2..0f66af5dc3 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -3070,7 +3070,7 @@ A directory on the host that can be accessed directly from the guest.
      </filesystem>
      <filesystem type='mount' accessmode='passthrough'>
          <driver type='virtiofs' queue='1024'/>
-         <binary path='/usr/libexec/virtiofsd' xattr='on'>
+         <binary path='/usr/libexec/virtiofsd' xattr='on' pool='32'>
             <cache mode='always'/>
             <lock posix='on' flock='on'/>
          </binary>
@@ -3188,7 +3188,9 @@ A directory on the host that can be accessed directly from the guest.
    the use of filesystem extended attributes. Caching can be tuned via the
    ``cache`` element, possible ``mode`` values being ``none`` and ``always``.
    Locking can be controlled via the ``lock`` element - attributes ``posix`` and
-   ``flock`` both accepting values ``on`` or ``off``. ( :since:`Since 6.2.0` )
+   ``flock`` both accepting values ``on`` or ``off``. ( :since:`Since 6.2.0` ).
+   Thread pool size limit can be tuned via the ``pool`` element.
+   ( :since:`Since 6.9.0` )
 ``source``
    The resource on the host that is being accessed in the guest. The ``name``
    attribute must be used with ``type='template'``, and the ``dir`` attribute
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index c25a742581..cd5de2ba80 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -2839,6 +2839,11 @@
           <ref name="virOnOff"/>
         </attribute>
       </optional>
+      <optional>
+        <attribute name="pool">
+          <ref name="unsignedInt"/>
+        </attribute>
+      </optional>
       <optional>
         <element name="cache">
           <optional>
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index efa5ac527b..9d06f8c75f 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -11588,6 +11588,7 @@ virDomainFSDefParseXML(virDomainXMLOptionPtr xmlopt,
         g_autofree char *cache = virXPathString("string(./binary/cache/@mode)", ctxt);
         g_autofree char *posix_lock = virXPathString("string(./binary/lock/@posix)", ctxt);
         g_autofree char *flock = virXPathString("string(./binary/lock/@flock)", ctxt);
+        g_autofree char *thread_pool_size = virXPathString("string(./binary/@pool)", ctxt);
         int val;
 
         if (queue_size && virStrToLong_ull(queue_size, NULL, 10, &def->queue_size) < 0) {
@@ -11597,6 +11598,14 @@ virDomainFSDefParseXML(virDomainXMLOptionPtr xmlopt,
             goto error;
         }
 
+        if (thread_pool_size &&
+            virStrToLong_ull(thread_pool_size, NULL, 10, &def->thread_pool_size) < 0) {
+            virReportError(VIR_ERR_XML_ERROR,
+                           _("cannot parse thread pool size '%s' for virtiofs"),
+                           thread_pool_size);
+            goto error;
+        }
+
         if (binary)
             def->binary = virFileSanitizePath(binary);
 
@@ -26191,6 +26200,9 @@ virDomainFSDefFormat(virBufferPtr buf,
                               virTristateSwitchTypeToString(def->xattr));
         }
 
+        if (def->thread_pool_size)
+            virBufferAsprintf(&binaryAttrBuf, " pool='%llu'", def->thread_pool_size);
+
         if (def->cache != VIR_DOMAIN_FS_CACHE_MODE_DEFAULT) {
             virBufferAsprintf(&binaryBuf, "<cache mode='%s'/>\n",
                               virDomainFSCacheModeTypeToString(def->cache));
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index cd344716a3..98ab0a51c7 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -860,6 +860,7 @@ struct _virDomainFSDef {
     bool symlinksResolved;
     char *binary;
     unsigned long long queue_size;
+    unsigned long long thread_pool_size;
     virTristateSwitch xattr;
     virDomainFSCacheMode cache;
     virTristateSwitch posix_lock;
diff --git a/src/qemu/qemu_virtiofs.c b/src/qemu/qemu_virtiofs.c
index 2e239cad66..e35c278a1b 100644
--- a/src/qemu/qemu_virtiofs.c
+++ b/src/qemu/qemu_virtiofs.c
@@ -126,6 +126,9 @@ qemuVirtioFSBuildCommandLine(virQEMUDriverConfigPtr cfg,
     virCommandPassFD(cmd, *fd, VIR_COMMAND_PASS_FD_CLOSE_PARENT);
     *fd = -1;
 
+    if (fs->thread_pool_size)
+        virCommandAddArgFormat(cmd, "--thread-pool-size=%llu", fs->thread_pool_size);
+
     virCommandAddArg(cmd, "-o");
     virBufferAddLit(&opts, "source=");
     virQEMUBuildBufferEscapeComma(&opts, fs->src->path);
-- 
2.27.0