Re: [RFC PATCH 0/5] mptcp support
On Fri, 2021-04-09 at 10:42 +0100, Daniel P. Berrangé wrote: > On Fri, Apr 09, 2021 at 10:34:30AM +0100, Daniel P. Berrangé wrote: > > On Thu, Apr 08, 2021 at 08:11:54PM +0100, Dr. David Alan Gilbert (git) > > wrote: > > > From: "Dr. David Alan Gilbert" > > > I had a quick go at trying NBD as well, but I think it needs > > > some work with the parsing of NBD addresses. > > > > In theory this is applicable to anywhere that we use sockets. > > Anywhere that is configured with the QAPI SocketAddress / > > SocketAddressLegacy type will get it for free AFAICT. > > The caveat is any servers which share the problem of prematurely > closing the listener socket that you fixed here for migration. For the records, there is an alternative to that, based on a more advanced and complex MPTCP configuration available only on even more recent kernels. MPTCP can be configured to accept additional subflows on a different listener, which will be managed (created and disposed) by the kernel with no additional user-space changes (beyond the MPTCP configuration). That will require also a suitable firewalld (if enabled) configuration (keeping the additional port open/accessible from the client). Finally such configuration can be even more complex e.g. the additional listener could be alternatively configured on the client side (!!!) and the server could be configured to create additional subflows connecting to such port (again no user-space changes needed, "only" more complex MPTCP configuration). Cheers, Paolo
Re: [RFC PATCH 4/5] migration/socket: Close the listener at the end
Hello, On Fri, 2021-04-09 at 10:10 +0100, Daniel P. Berrangé wrote: > On Thu, Apr 08, 2021 at 08:11:58PM +0100, Dr. David Alan Gilbert (git) wrote: > > From: "Dr. David Alan Gilbert" > > > > Delay closing the listener until the cleanup hook at the end; mptcp > > needs the listener to stay open while the other paths come in. > > So you're saying that when the 'accept(2)' call returns, we are only > guaranteed to have 1 single path accepted, when accept() returns it's guaranteed that the first path (actually subflow) has been created. Other subflows can be already available, or can be created later. > and the other paths > will be accepted by the kernel asynchronously ? Hence we need to > keep listening, even though we're not going to call accept(2) again > ourselves ? Exactly, the others subflows will be created by the kernel as needed (according to the configuration and the following MPTCP handshakes) and will _not_ be exposed directly to the user-space as additional fds. The fd returned by accept() refers to the main MPTCP socket (that is, the "aggregated" entity), and not to some specific subflow. Please let me know if the above clarifies in some way. Thanks! Paolo
Re: [RFC PATCH 0/5] mptcp support
On Fri, 2021-04-09 at 10:34 +0100, Daniel P. Berrangé wrote: > On Thu, Apr 08, 2021 at 08:11:54PM +0100, Dr. David Alan Gilbert (git) wrote: > > From: "Dr. David Alan Gilbert" > > > > Hi, > > This RFC set adds support for multipath TCP (mptcp), > > in particular on the migration path - but should be extensible > > to other users. > > > > Multipath-tcp is a bit like bonding, but at L3; you can use > > it to handle failure, but can also use it to split traffic across > > multiple interfaces. > > > > Using a pair of 10Gb interfaces, I've managed to get 19Gbps > > (with the only tuning being using huge pages and turning the MTU up). > > > > It needs a bleeding-edge Linux kernel (in some older ones you get > > false accept messages for the subflows), and a C lib that has the > > constants defined (as current glibc does). > > > > To use it you just need to append ,mptcp to an address; > > > > -incoming tcp:0:,mptcp > > migrate -d tcp:192.168.11.20:,mptcp > > What happens if you only enable mptcp flag on one side of the > stream (whether client or server), does it degrade to boring > old single path TCP, or does it result in an error ? If the mptcp handshake fails by any means - e.g. one side does not ask for MPTCP - the connection fallbacks to plain TCP in a transparent way. > > I had a quick go at trying NBD as well, but I think it needs > > some work with the parsing of NBD addresses. > > In theory this is applicable to anywhere that we use sockets. > Anywhere that is configured with the QAPI SocketAddress / > SocketAddressLegacy type will get it for free AFAICT. > > Anywhere that is configured via QemuOpts will need an enhancement. > > IOW, I would think NBD already works if you configure NBD via > QMP with nbd-server-start, or block-export-add. qemu-nbd will > need cli options added. > > The block layer clients for NBD, Gluster, Sheepdog and SSH also > all get it for free when configured va QMP, or -blockdev AFAICT > > Legacy blocklayer filename syntax would need extra parsing, or > we can just not bother and say if you want new features, use > blockdev. > > > Overall this is impressively simple. > > It feels like it obsoletes the multifd migration code, at least > if you assume Linux platform and new enough kernel ? > > Except TLS... We already bottleneck on TLS encryption with > a single FD, since userspace encryption is limited to a > single thread. > > There is the KTLS feature which offloads TLS encryption/decryption > to the kernel. This benefits even regular single FD performance, > because the encrytion work can be done by the kernel in a separate > thread from the userspace IO syscalls. > > Any idea if KTLS is fully compatible with MPTCP ? Ouch! So far is not supported. Both KTLS and MPTCP use/need ULP (Upper Layer Protocol, a kernel way of hijaking core TCP features) and we can have a single ULP per socket, so possibly that there is some technical show- stopper there. At very least is not in our short term roadmap, but I guess we can updated that based on user needs. Thanks! Paolo
[Qemu-devel] virtual PC block driver status
hello, As noted before (http://lists.gnu.org/archive/html/qemu-devel/2006-10/msg00153.html) Microsoft has published the format of virtual pc drive VHD. It should be used also by xen. The specs are available here: http://download.microsoft.com/download/f/f/e/ffef50a5-07dd-4cf8-aaa3-442c0673a029/Virtual%20Hard%20Disk%20Format%20Spec_10_18_06.doc I would like to implement proper VHD support for qemu using such information. In order to not duplicate effort, I would like to know if some one is already working on updating current vpc block driver. Best regards, Paolo -- Email.it, the professional e-mail, gratis per te: http://www.email.it/f Sponsor: Le speciali Offerte di Benvenuto di Cassine di Pietra: * scopra il gusto ed i vantaggi delle tradizioni contadine * Clicca qui: http://adv.email.it/cgi-bin/foclick.cgi?mid=3924d=16-2
