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Re: [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap |
Date: |
Tue, 15 Jul 2014 16:59:39 +0200 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Mon, Jul 14, 2014 at 10:44:58AM +0000, Wangkai (Kevin,C) wrote:
> Here the detail network:
>
> +--------------------------------------------+
> | The host add tap1 and eth10 to bridge 'br1'| +--------+
> | +------------+ | | send |
> | | VM eth1-+-tap1 --- bridge --- eth10 --+---------------------+ packets|
> | +------------+ | | |
> +--------------------------------------------+ +--------+
>
> Qemu start vm by virtio, use tap interface, option is:
> -net nic,vlan=101, model=virtio -net
> tap,vlan=101,ifname=tap1,script=no,downscript=no
Use the newer -netdev/-device syntax to get offload support and slightly
better performance:
-netdev tap,id=tap0,ifname=tap1,script=no,downscript=no \
-device virtio-net-pci,netdev=tap0
> And add tap1 and eth10 to bridge br1 in the host:
> Brctl addif br1 tap1
> Brctl addif br1 eth10
>
> total recv 505387 time 2000925 us:
> means call tap_send once dealing 505387 packets, the packet payload was 300
> bytes, and
> time use for tap_send() was 2,000,925 micro-seconds, time was measured by
> record time stamp
> at function tap_send() start and end.
>
> We just test the performance of VM.
That is 150 MB of incoming packets in a single tap_send(). Network rx
queues are maybe a few 1000 packets so I wonder what is going on here.
Maybe more packets are arriving while QEMU is reading them and we keep
looping. That's strange though because the virtio-net rx virtqueue
should fill up (it only has 256 entries).
Can you investigate more and find out exactly what is going on? It's
not clear yet that adding a budget is the solution or just hiding a
deeper problem.
Stefan
pgpdRaHB1fahU.pgp
Description: PGP signature
- [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap, Wangkai (Kevin,C), 2014/07/10
- Re: [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap, Stefan Hajnoczi, 2014/07/11
- Re: [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap, Wangkai (Kevin,C), 2014/07/13
- Re: [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap, Stefan Hajnoczi, 2014/07/14
- Re: [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap, Wangkai (Kevin,C), 2014/07/14
- Re: [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap,
Stefan Hajnoczi <=
- Re: [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap, Wangkai (Kevin,C), 2014/07/16
- Re: [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap, Wangkai (Kevin,C), 2014/07/16
- Re: [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap, Jason Wang, 2014/07/17
- Re: [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap, Wangkai (Kevin,C), 2014/07/17
Re: [Qemu-devel] [PATCH] Tap: fix vcpu long time io blocking on tap, Stefan Hajnoczi, 2014/07/17