Re: [Qemu-devel] [PATCH v8 0/6] fsdev: qmp interface for io throttling

[Alberto Garcia]

On Wed 30 Aug 2017 02:10:53 PM CEST, Pradeep Jagadeesh wrote:

>> I'm trying to read from an 9p share that has limits set with hmp
>> fsdev_set_io_throttle and I'm having some problems.

Here's one simple way to reproduce it:

1) Launch qemu with

   -fsdev local,security_model=none,id=fs0,path=/some/files
   -device virtio-9p-pci,fsdev=fs0,mount_tag=fs0

2) In the guest, mount the fs0 share in /mnt

3) Run this hmp command

   fsdev_set_io_throttle fs0 0 4096 0 0 0 0

4) In the guest, start reading some large file from the 9p share:

   dd if=/mnt/large_file of=/dev/null bs=4k iflag=direct status=progress

5) Check the progress, reading speed should be around 4k per second.

6) While dd is still running, change the I/O limits:

   fsdev_set_io_throttle fs0 0 8192 0 0 0 0

7) If you check the status of the dd command, reading should be faster
   now. Instead, it is stalled.

Berto