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Re: [PATCH v2 0/1] migration: multifd live migration improvement
From: |
Li Zhang |
Subject: |
Re: [PATCH v2 0/1] migration: multifd live migration improvement |
Date: |
Tue, 7 Dec 2021 16:32:36 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 |
On 12/7/21 3:16 PM, Daniel P. Berrangé wrote:
On Tue, Dec 07, 2021 at 02:45:10PM +0100, Li Zhang wrote:
On 12/6/21 8:54 PM, Dr. David Alan Gilbert wrote:
* Li Zhang (lizhang@suse.de) wrote:
When testing live migration with multifd channels (8, 16, or a bigger number)
and using qemu -incoming (without "defer"), if a network error occurs
(for example, triggering the kernel SYN flooding detection),
the migration fails and the guest hangs forever.
The test environment and the command line is as the following:
QEMU verions: QEMU emulator version 6.2.91 (v6.2.0-rc1-47-gc5fbdd60cf)
Host OS: SLE 15 with kernel: 5.14.5-1-default
Network Card: mlx5 100Gbps
Network card: Intel Corporation I350 Gigabit (1Gbps)
Source:
qemu-system-x86_64 -M q35 -smp 32 -nographic \
-serial telnet:10.156.208.153:4321,server,nowait \
-m 4096 -enable-kvm -hda /var/lib/libvirt/images/openSUSE-15.3.img \
-monitor stdio
Dest:
qemu-system-x86_64 -M q35 -smp 32 -nographic \
-serial telnet:10.156.208.154:4321,server,nowait \
-m 4096 -enable-kvm -hda /var/lib/libvirt/images/openSUSE-15.3.img \
-monitor stdio \
-incoming tcp:1.0.8.154:4000
(qemu) migrate_set_parameter max-bandwidth 100G
(qemu) migrate_set_capability multifd on
(qemu) migrate_set_parameter multifd-channels 16
The guest hangs when executing the command: migrate -d tcp:1.0.8.154:4000.
If a network problem happens, TCP ACK is not received by destination
and the destination resets the connection with RST.
No. Time Source Destination Protocol Length Info
119 1.021169 1.0.8.153 1.0.8.154 TCP 1410 60166 →
4000 [PSH, ACK] Seq=65 Ack=1 Win=62720 Len=1344 TSval=1338662881
TSecr=1399531897
No. Time Source Destination Protocol Length Info
125 1.021181 1.0.8.154 1.0.8.153 TCP 54 4000 →
60166 [RST] Seq=1 Win=0 Len=0
kernel log:
[334520.229445] TCP: request_sock_TCP: Possible SYN flooding on port 4000.
Sending cookies. Check SNMP counters.
[334562.994919] TCP: request_sock_TCP: Possible SYN flooding on port 4000.
Sending cookies. Check SNMP counters.
[334695.519927] TCP: request_sock_TCP: Possible SYN flooding on port 4000.
Sending cookies. Check SNMP counters.
[334734.689511] TCP: request_sock_TCP: Possible SYN flooding on port 4000.
Sending cookies. Check SNMP counters.
[335687.740415] TCP: request_sock_TCP: Possible SYN flooding on port 4000.
Sending cookies. Check SNMP counters.
[335730.013598] TCP: request_sock_TCP: Possible SYN flooding on port 4000.
Sending cookies. Check SNMP counters.
Should we document somewhere how to avoid that? Is there something we
should be doing in the connection code to avoid it?
We should use the command line -incoming defer in QEMU command line instead
of -incoming ip:port.
And the backlog of the socket will be set as the same as multifd channels,
this problem doesn't happen as far as I test.
If we use --incoming ip:port in the QEMU command line, the backlog of the
socket is always 1, it will cause the SYN flooding.
Do we send migration parameters from the src to the dst QEMU ?
No, I don't think we send migration parameters from the src to the dest
QEMU.
I set migration parameters on both sides from qemu monitor seperately.
There are a bunch of things that we need to set to the same
value on the src and dst. If we sent any relevant MigrationParameters
fields to the dst, when the first/main migration chanel is opened, it
could validate that it is configured in a way that is compatible with
the src. If it isn't, it can drop the main channel immediately. This
would trigger the src to fail the migration and we couldn't get stuck
setting up the secondary data channels for multifd.
OK, currently, we have same parameters on both sides if we set them the
same parameters.
If we use -incoming tcp:ip:port because the multifd is disabled by
default and backlog is 1 when the socket is created.
Here is the function which set the backlog:
static void
socket_start_incoming_migration_internal(SocketAddress *saddr,
Error **errp)
{
QIONetListener *listener = qio_net_listener_new();
MigrationIncomingState *mis = migration_incoming_get_current();
size_t i;
int num = 1;
qio_net_listener_set_name(listener, "migration-socket-listener");
if (migrate_use_multifd()) {
num = migrate_multifd_channels();
}
...
}
The process with -incoming tcp:ip:port is as the following:
1. Create qemu process with command line -incoming tcp:ip:port
2. socket_start_incoming_migration_internal is called and backlog is:
num=1, multifd is disabled, num = migrate_multifd_channels() is not called
3. Enable multifd and set multifd parameters, but the backlog is still
1, because the it couldn't be changed anymore.
4. Run migration
The process with -incoming defer is as the following:
1. Create qemu process with command line -incoming defer
2. Enable multifd and set multifd parameters
3. Execute the command (qemu) migrate_incoming tcp:ip:port
4. Call socket_start_incoming_migration_internal then the backlog is
set: num = migrate_multifd_channels();
5. Run migration
Regards,
Daniel