[Qemu-devel] [Bug 1253563] [NEW] bad performance with rng-egd backend

From: Amos Kong <1253563@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Qemu-devel] [Bug 1253563] [NEW] bad performance with rng-egd backend
Date: Thu, 21 Nov 2013 09:24:11 -0000	[thread overview]
Message-ID: <20131121092412.27241.16050.malonedeb@gac.canonical.com> (raw)
In-Reply-To: 20131121092412.27241.16050.malonedeb@gac.canonical.com

Public bug reported:

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

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1253563

Title:
  bad performance with rng-egd backend

Status in QEMU:
  New

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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