[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c
From: |
Jan Kiszka |
Subject: |
Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c |
Date: |
Wed, 30 May 2012 22:23:55 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
On 2012-05-30 22:23, Luigi Rizzo wrote:
> Hi,
> while testing qemu with netmap (see [Note 1] for details) on e1000
> emulation, i noticed that my sender program using a custom backend
> [Note 2] could reach 1 Mpps (million packets per second) but on the
> receive side i was limited to 50 Kpps (and CPU always below 5%).
>
> The problem was fixed by the following one-line addition to
> hw/e1000.c :: e1000_mmio_write() , to wakeup the qemu mainloop and
> check that some buffers might be available.
>
> --- hw/e1000.c.orig 2012-02-17 20:45:39.000000000 +0100
> +++ hw/e1000.c 2012-05-30 20:01:52.000000000 +0200
> @@ -919,6 +926,7 @@
> DBGOUT(UNKNOWN, "MMIO unknown write
> addr=0x%08x,val=0x%08"PRIx64"\n",
> index<<2, val);
> }
> + qemu_notify_event();
> }
>
> static uint64_t
>
> With this fix, the read throughput reaches 1 Mpps matching the write
> speed. Now the system becomes CPU-bound, but this opens the way to
> more optimizations in the emulator.
>
> The same problem seems to exist on other network drivers, e.g.
> hw/rtl8139.c and others. The only one that seems to get it
> right is virtio-net.c
>
> I think it would be good if this change could make it into
> the tree.
>
> [Note 1] Netmap ( http://info.iet.unipi.it/~luigi/netmap )
> is an efficient mechanism for packet I/O that bypasses
> the network stack and provides protected access to the
> network adapter from userspace.
> It works especially well on top of qemu because the
> kernel needs only to trap a single register access
> for each batch of packets.
>
> [Note 2] the custom backend is a virtual local ethernet
> called VALE, implemented as a kernel module on the host,
> that extends netmap to implement communication
> between virtual machines.
> VALE is extremely efficient, currently delivering about
> 10~Mpps with 60-byte frames, and 5~Mpps with 1500-byte frames.
> The 1 Mpps rates i mentioned are obtained between qemu instances
> running in userspace on FreeBSD (no kernel acceleration whatsoever)
> and using VALE as a communication mechanism.
"Custom backend" == you patched QEMU? Or what backend are you using?
This sounds a lot like [1] and suggests that you are either a) using
slirp in a version that doesn't contain that fix yet (before 1.1-rcX) or
b) wrote a backend that suffers from a similar bug.
Jan
[1] http://thread.gmane.org/gmane.comp.emulators.qemu/144433
signature.asc
Description: OpenPGP digital signature
- [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c, Luigi Rizzo, 2012/05/30
- Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c,
Jan Kiszka <=
- Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c, Luigi Rizzo, 2012/05/30
- Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c, Jan Kiszka, 2012/05/30
- Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c, Luigi Rizzo, 2012/05/30
- Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c, Jan Kiszka, 2012/05/30
- Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c, Luigi Rizzo, 2012/05/30
- Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c, Paolo Bonzini, 2012/05/31
- Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c, Luigi Rizzo, 2012/05/31
- Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c, Jan Kiszka, 2012/05/31
- Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c, Jan Kiszka, 2012/05/31
- Re: [Qemu-devel] Proposed patch: huge RX speedup for hw/e1000.c, Luigi Rizzo, 2012/05/31