[pve-devel] [PATCH v2 docs 1/2] qm: IO thread: be more precise about how QEMU handles IO

[pve-devel] [PATCH v2 docs 1/2] qm: IO thread: be more precise about how QEMU handles IO

[Fiona Ebner]

Reported in the community forum[0].

The setting can already help with a single disk. Without the option,
there is not one IO thread as the old wording suggested, but IO is
handled in the main event loop or vCPU threads (see the kvm man page).

[0]: https://forum.proxmox.com/threads/118390/post-518532

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---

Changes from v1:
    * Rebase on current master.

 qm.adoc | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/qm.adoc b/qm.adoc
index 644ece5..900ecae 100644
--- a/qm.adoc
+++ b/qm.adoc
@@ -249,12 +249,11 @@ Note that *SSD emulation* is not supported on *VirtIO Block* drives.
 [[qm_hard_disk_iothread]]
 IO Thread
 ^^^^^^^^^
-The option *IO Thread* can only be used when using a disk with the
-*VirtIO* controller, or with the *SCSI* controller, when the emulated controller
- type is  *VirtIO SCSI single*.
-With this enabled, QEMU creates one I/O thread per storage controller,
-rather than a single thread for all I/O. This can increase performance when
-multiple disks are used and each disk has its own storage controller.
+The option *IO Thread* can only be used when using a disk with the *VirtIO*
+controller, or with the *SCSI* controller, when the emulated controller type is
+*VirtIO SCSI single*. With *IO Thread* enabled, QEMU creates one I/O thread per
+storage controller, rather than handling all I/O in the main event loop or vCPU
+threads. This can increase performance, because of improved work distribution.
 
 
 [[qm_cpu]]
-- 
2.30.2

[pve-devel] [PATCH v2 docs 2/2] qm: IO thread: mention that setting can also help with hangs

[Fiona Ebner]

See https://bugzilla.kernel.org/show_bug.cgi?id=199727

Reported-by: Roland Kletzing <devzero@web.de>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---

New in v2.

 qm.adoc | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/qm.adoc b/qm.adoc
index 900ecae..c3e876f 100644
--- a/qm.adoc
+++ b/qm.adoc
@@ -253,7 +253,9 @@ The option *IO Thread* can only be used when using a disk with the *VirtIO*
 controller, or with the *SCSI* controller, when the emulated controller type is
 *VirtIO SCSI single*. With *IO Thread* enabled, QEMU creates one I/O thread per
 storage controller, rather than handling all I/O in the main event loop or vCPU
-threads. This can increase performance, because of improved work distribution.
+threads. This can increase performance, because of improved work distribution
+and also avoid hangs under very I/O-intensive host workloads, because other
+threads won't be blocked waiting for I/O.
 
 
 [[qm_cpu]]
-- 
2.30.2

[pve-devel] applied-series: [PATCH v2 docs 1/2] qm: IO thread: be more precise about how QEMU handles IO

[Thomas Lamprecht]

On 20/12/2022 12:24, Fiona Ebner wrote:
> Reported in the community forum[0].
> 
> The setting can already help with a single disk. Without the option,
> there is not one IO thread as the old wording suggested, but IO is
> handled in the main event loop or vCPU threads (see the kvm man page).
> 
> [0]: https://forum.proxmox.com/threads/118390/post-518532
> 
> Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
> ---
> 
> Changes from v1:
>     * Rebase on current master.
> 
>  qm.adoc | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
>

applied, thanks!