[Bug 1253563] Re: bad performance with rng-egd backend

[Amos Jianjun Kong]

Let's close this bug, it's passed 6 years.

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Title:
  bad performance with rng-egd backend

Status in QEMU:
  Incomplete

Bug description:
  
  1. create listen socket
  # cat /dev/random | nc -l localhost 1024

  2. start vm with rng-egd backend

  ./x86_64-softmmu/qemu-system-x86_64 --enable-kvm -mon 
chardev=qmp,mode=control,pretty=on -chardev 
socket,id=qmp,host=localhost,port=1234,server,nowait -m 2000 -device 
virtio-net-pci,netdev=h1,id=vnet0 -netdev tap,id=h1 -vnc :0 -drive 
file=/images/RHEL-64-virtio.qcow2 \
  -chardev socket,host=localhost,port=1024,id=chr0 \
  -object rng-egd,chardev=chr0,id=rng0 \
  -device virtio-rng-pci,rng=rng0,max-bytes=1024000,period=1000

  (guest) # dd if=/dev/hwrng of=/dev/null

  note: cancelling dd process by Ctrl+c, it will return the read speed.

  Problem:   the speed is around 1k/s

  ===================

  If I use rng-random backend (filename=/dev/random), the speed is about
  350k/s).

  It seems that when the request entry is added to the list, we don't read the 
data from queue list immediately.
  The chr_read() is delayed, the virtio_notify() is delayed.  the next request 
will also be delayed. It effects the speed.

  I tried to change rng_egd_chr_can_read() always returns 1,  the speed
  is improved to (about 400k/s)

  Problem: we can't poll the content in time currently

  
  Any thoughts?

  Thanks, Amos

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