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


From: Pradeep Jagadeesh
Subject: Re: [Qemu-devel] [PATCH v8 0/6] fsdev: qmp interface for io throttling
Date: Wed, 30 Aug 2017 17:07:29 +0200
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

On 8/30/2017 4:54 PM, Alberto Garcia wrote:
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.

Thanks for the steps, I did reproduce the issue easily.
Looking into the code, may be we also need to try the same with the block devices.

-Pradeep

Berto





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