From: Ingo Molnar <mingo@elte.hu>
To: Alexander Graf <agraf@suse.de>
Cc: Asias He <asias.hejun@gmail.com>,
Anthony Liguori <anthony@codemonkey.ws>,
Stefan Hajnoczi <stefanha@gmail.com>,
Pekka Enberg <penberg@kernel.org>,
Cyrill Gorcunov <gorcunov@gmail.com>,
Sasha Levin <levinsasha928@gmail.com>,
Prasad Joshi <prasadjoshi124@gmail.com>,
kvm@vger.kernel.org
Subject: Re: [PATCH v2 00/31] Implement user mode network for kvm tools
Date: Mon, 4 Jul 2011 11:11:27 +0200 [thread overview]
Message-ID: <20110704091127.GA22943@elte.hu> (raw)
In-Reply-To: <46843B06-C11F-4FD3-8A85-54DDE0DF5D3D@suse.de>
* Alexander Graf <agraf@suse.de> wrote:
> >> I don't see how it would. Once you overrun device buffers, you
> >> have to do something. Either you drop packets or you stall the
> >> guest. I'd usually prefer the former :).
> >
> > What scenario do you see where we'd have to drop packets?
> >
> > When the guest sends packets, we send them over to the host TCP
> > socket - no blocking.
>
> When the guest sends packets, I'd hope you have 2 threads:
>
> * vcpu
> * virtio network queue process
>
> So those two run in parallel now, with the network queue processing
> packets while the vcpu pushes packets into the ring. What if the
> network thread is slower than the vcpu fills the ring? You only
> have so many entries in a vring.
>
> > When the host receives packets it should only read data out of
> > the host socket(s) if the vring buffer suggests that there's
> > space available.
>
> I agree :).
>
> > So i don't see we'd need to drop packets or block things - we
> > just have to react to packets and to vring space availability in
> > a straightforward way.
>
> Well, the only way for the sending path is to stall the vcpu,
> otherwise the guest figures "oh, I can't push packets into the
> vring, let's just drop it", no?
No, that's not how the Linux TCP/IP implementation works.
Filled up TX rings are pretty normal on physical hardware: we do not
drop packets but the TCP state machine keeps buffering and filling
the device as it can.
The same will happen with virtual guests as well - there's no packet
dropping nor 'blocking of the whole guest'.
Thanks,
Ingo
next prev parent reply other threads:[~2011-07-04 9:11 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-30 8:40 [PATCH v2 00/31] Implement user mode network for kvm tools Asias He
2011-06-30 8:40 ` [PATCH v2 01/31] kvm tools: Introduce ethernet frame buffer system for uip Asias He
2011-06-30 8:40 ` [PATCH v2 02/31] kvm tools: Add ARP support " Asias He
2011-06-30 8:40 ` [PATCH v2 03/31] kvm tools: Add IPV4 " Asias He
2011-06-30 8:40 ` [PATCH v2 04/31] kvm tools: Implement IP checksum " Asias He
2011-06-30 8:40 ` [PATCH v2 05/31] kvm tools: Add ICMP support " Asias He
2011-06-30 8:40 ` [PATCH v2 06/31] kvm tools: Introduce struct uip_udp to present UDP package Asias He
2011-06-30 8:40 ` [PATCH v2 07/31] kvm tools: Introduce struct uip_pseudo_hdr to present UDP pseudo header Asias He
2011-06-30 8:40 ` [PATCH v2 08/31] kvm tools: Introduce struct uip_udp_socket Asias He
2011-06-30 8:40 ` [PATCH v2 09/31] kvm tools: Add two helpers to return UDP {header, total} length Asias He
2011-06-30 8:40 ` [PATCH v2 10/31] kvm tools: Add helper to return ethernet header length Asias He
2011-06-30 8:40 ` [PATCH v2 11/31] kvm tools: Implement uip_csum_udp() to calculate UDP checksum Asias He
2011-06-30 8:41 ` [PATCH v2 12/31] kvm tools: Add UDP support for uip Asias He
2011-07-01 11:46 ` Ingo Molnar
2011-07-01 15:24 ` Asias He
2011-06-30 8:41 ` [PATCH v2 13/31] kvm tools: Introduce struct uip_tcp to present TCP package Asias He
2011-06-30 8:41 ` [PATCH v2 14/31] kvm tools: Introduce struct uip_tcp_socket Asias He
2011-06-30 8:41 ` [PATCH v2 15/31] kvm tools: Add helpers to return TCP {header, total, payload} length Asias He
2011-06-30 8:41 ` [PATCH v2 16/31] kvm tools: Add helper to return start address of TCP payload Asias He
2011-06-30 8:41 ` [PATCH v2 17/31] kvm tools: Add helpers to test whether SYN or FIN bit is set Asias He
2011-06-30 8:41 ` [PATCH v2 18/31] kvm tools: Add helper to allocate and get TCP initial sequence number Asias He
2011-06-30 8:41 ` [PATCH v2 19/31] kvm tools: Implement uip_csum_tcp() to calculate TCP checksum Asias He
2011-06-30 8:41 ` [PATCH v2 20/31] kvm tools: Add TCP support for uip Asias He
2011-06-30 8:41 ` [PATCH v2 21/31] kvm tools: Introduce uip_init() " Asias He
2011-06-30 8:41 ` [PATCH v2 22/31] kvm tools: Introduce uip_tx() " Asias He
2011-06-30 8:41 ` [PATCH v2 23/31] kvm tools: Introduce uip_rx() " Asias He
2011-06-30 8:41 ` [PATCH v2 24/31] kvm tools: Add MACRO for user and tap mode for virtio net Asias He
2011-06-30 8:41 ` [PATCH v2 25/31] kvm tools: Reanme net_device to net_dev Asias He
2011-06-30 8:41 ` [PATCH v2 26/31] kvm tools: Introduce -net {user, tap, none} options for virtio net Asias He
2011-06-30 8:41 ` [PATCH v2 27/31] kvm tools: Change default guest MAC address to 00:15:15:15:15:15 Asias He
2011-06-30 8:41 ` [PATCH v2 28/31] kvm tools: Make virtio net work with user mode network Asias He
2011-06-30 8:41 ` [PATCH v2 29/31] kvm tools: Make default network mode to user mode Asias He
2011-06-30 8:41 ` [PATCH v2 30/31] kvm tools: Make default host ip address to 192.168.33.1 Asias He
2011-06-30 8:41 ` [PATCH v2 31/31] kvm tools: Introduce struct net_dev_operations Asias He
2011-06-30 8:56 ` [PATCH v2 00/31] Implement user mode network for kvm tools Stefan Hajnoczi
2011-06-30 15:32 ` Anthony Liguori
2011-07-01 0:18 ` Asias He
2011-07-01 11:53 ` Ingo Molnar
2011-07-01 13:46 ` Alexander Graf
2011-07-02 9:45 ` Pekka Enberg
2011-07-02 10:30 ` Ingo Molnar
2011-07-02 11:19 ` Alexander Graf
2011-07-02 11:27 ` Pekka Enberg
2011-07-02 12:31 ` Alexander Graf
2011-07-03 19:42 ` Ingo Molnar
2011-07-03 22:15 ` Alexander Graf
2011-07-04 9:11 ` Ingo Molnar [this message]
2011-07-04 9:30 ` Alexander Graf
2011-07-04 9:43 ` Ingo Molnar
2011-07-02 9:42 ` Pekka Enberg
2011-06-30 23:38 ` Asias He
2011-07-01 16:50 ` Stefan Hajnoczi
2011-07-01 20:36 ` Pekka Enberg
2011-07-02 3:49 ` Asias He
2011-07-02 9:02 ` Ingo Molnar
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