[libvirt PATCH 1/2] conf: virtiofs: add thread_pool element

[Michal Prívozník]

On 6/10/22 15:25, Ján Tomko wrote:
> Add an element to configure the thread pool size:
> 
> ...
> <binary>
>   <thread_pool size='16'/>
> </binary>
> ...
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=2072905
> 
> Signed-off-by: Ján Tomko <jtomko at redhat.com>
> ---
>  docs/formatdomain.rst                              |  6 ++++++
>  src/conf/domain_conf.c                             | 14 ++++++++++++++
>  src/conf/domain_conf.h                             |  1 +
>  src/conf/schemas/domaincommon.rng                  |  9 +++++++++
>  tests/qemuxml2argvdata/vhost-user-fs-fd-memory.xml |  1 +
>  5 files changed, 31 insertions(+)
> 
> diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
> index 7da625380c..e8bff7632a 100644
> --- a/docs/formatdomain.rst
> +++ b/docs/formatdomain.rst
> @@ -3329,6 +3329,7 @@ A directory on the host that can be accessed directly from the guest.
>              <cache mode='always'/>
>              <sandbox mode='namespace'/>
>              <lock posix='on' flock='on'/>
> +            <thread_pool size='16'/>

I'm not sure this is extensible. I mean <thread_pool/> is pretty
specific. <thread pool_size='16'/> might look better, but then what is
<thread/>? I don't have any better idea, sorry.

>           </binary>
>           <source dir='/path'/>
>           <target dir='mount_tag'/>
> @@ -3462,6 +3463,11 @@ A directory on the host that can be accessed directly from the guest.
>     ``chroot``, see the
>     `virtiofsd documentation <https://qemu.readthedocs.io/en/latest/tools/virtiofsd.html>`__
>     for more details. ( :since:`Since 7.2.0` )
> +   Element ``thread_pool`` accepts one attribute ``size`` which defines the
> +   maximum thread pool size. A value of "0" disables the pool.
> +   The thread pool helps increase the number of requests in flight when used with
> +   storage that has a higher latency.  However, it has an overhead, and so for
> +   fast, low latency filesystems, it may be best to turn it off. ( :since:`Since 8.5.0` )
>  ``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/src/conf/domain_conf.c b/src/conf/domain_conf.c
> index 761c3f4d87..05fac7b39c 100644
> --- a/src/conf/domain_conf.c
> +++ b/src/conf/domain_conf.c
> @@ -2476,6 +2476,8 @@ virDomainFSDefNew(virDomainXMLOption *xmlopt)
>  
>      ret->src = virStorageSourceNew();
>  
> +    ret->thread_pool_size = -1;
> +
>      if (xmlopt &&
>          xmlopt->privateData.fsNew &&
>          !(ret->privateData = xmlopt->privateData.fsNew()))
> @@ -9914,6 +9916,7 @@ virDomainFSDefParseXML(virDomainXMLOption *xmlopt,
>      if (def->fsdriver == VIR_DOMAIN_FS_DRIVER_TYPE_VIRTIOFS) {
>          g_autofree char *queue_size = virXPathString("string(./driver/@queue)", ctxt);
>          g_autofree char *binary = virXPathString("string(./binary/@path)", ctxt);
> +        g_autofree char *thread_pool_size = virXPathString("string(./binary/thread_pool/@size)", ctxt);
>          xmlNodePtr binary_node = virXPathNode("./binary", ctxt);
>          xmlNodePtr binary_lock_node = virXPathNode("./binary/lock", ctxt);
>          xmlNodePtr binary_cache_node = virXPathNode("./binary/cache", ctxt);
> @@ -9926,6 +9929,13 @@ virDomainFSDefParseXML(virDomainXMLOption *xmlopt,
>              goto error;
>          }
>  
> +        if (thread_pool_size && virStrToLong_i(thread_pool_size, NULL, 10, &def->thread_pool_size) < 0) {

Very long line.

> +            virReportError(VIR_ERR_XML_ERROR,
> +                           _("cannot parse thread pool size '%s' for virtiofs"),
> +                           queue_size);
> +            goto error;
> +        }
> +
>          if (binary)
>              def->binary = virFileSanitizePath(binary);
>  
> @@ -24211,6 +24221,10 @@ virDomainFSDefFormat(virBuffer *buf,
>          }
>  
>          virXMLFormatElement(&binaryBuf, "lock", &lockAttrBuf, NULL);
> +
> +        if (def->thread_pool_size >= 0)
> +            virBufferAsprintf(&binaryBuf, "<thread_pool size='%i'/>\n", def->thread_pool_size);

I believe %d is preferred.

> +
>      }
>  

Michal