passt/test/perf/passt_tcp, branch 2024_06_24.1ee2eca

test/perf: Simplify calculation of "omit" time for TCP throughput

2023-11-07T08:56:24+00:00

For the TCP throughput tests, we use iperf3's -O "omit" option which
ignores results for the given time at the beginning of the test.  Currently
we calculate this as 1/6th of the test measurement time.  The purpose of
-O, however, is to skip over the TCP slow start period, which in no way
depends on the overall length of the test.

The slow start time is roughly speaking
    log_2 ( max_window_size / MSS ) * round_trip_time
These factors all vary between tests and machines we're running on, but we
can estimate some reasonable bounds for them:
  * The maximum window size is bounded by the buffer sizes at each end,
    which shouldn't exceed 16MiB
  * The mss varies with the MTU we use, but the smallest we use in tests is
    ~256 bytes
  * Round trip time will vary with the system, but with these essentially
    local transfers it will typically be well under 1ms (on my laptop it is
    closer to 0.03ms)

That gives a worst case slow start time of about 16ms.  Setting an omit
time of 0.1s uniformly is therefore more than enough, and substantially
smaller than what we calculate now for the default case (10s / 6 ~= 1.7s).

This reduces total time for the standard benchmark run by around 30s.

Signed-off-by: David Gibson 
Signed-off-by: Stefano Brivio

test/perf: Remove unnecessary --pacing-timer options

2023-11-07T08:56:21+00:00

We always set --pacing-timer when invoking iperf3.  However, the iperf3
man page implies this is only relevant for the -b option.  We only use the
-b option for the UDP tests, not TCP, so remove --pacing-timer from the TCP
cases.

Signed-off-by: David Gibson 
Signed-off-by: Stefano Brivio

test/perf: "MTU" changes in passt_tcp host to guest aren't useful

2023-11-07T08:56:18+00:00

The TCP packet size used on the passt L2 link (qemu socket) makes a huge
difference to passt/pasta throughput; many of passt's overheads (chiefly
syscalls) are per-packet.

That packet size is largely determined by the MTU on the L2 link, so we
benchmark for a number of different MTUs.  That works well for the guest to
host transfers.  For the host to guest transfers, we purport to test for
different MTUs, but we're not actually adjusting anything interesting.

The host to guest transfers adjust the MTU on the "host's" (actually ns)
loopback interface.  However, that only affects the packet size for the
socket going to passt, not the packet size for the L2 link that passt
manages - passt can and will repack the stream into packets of its own
size.  Since the depacketization on that socket is handled by the kernel it
doesn't have a lot of bearing on passt's performance.

We can't fix this by changing the L2 link MTU from the guest side (as we do
for guest to host), because that would only change the guest's view of the
MTU, passt would still think it has the large MTU.  We could test this by
using the --mtu option to passt, but that would require restarting passt
for each run, which is awkward in the current setup.  So, for now, drop all
the "small MTU" tests for host to guest.

Signed-off-by: David Gibson 
Signed-off-by: Stefano Brivio

test/perf: Start iperf3 server less often

2023-11-07T08:56:10+00:00

Currently we start both the iperf3 server(s) and client(s) afresh each time
we want to make a bandwidth measurement.  That's not really necessary as
usually a whole batch of bandwidth measurements can use the same server.

Split up the iperf3 directive into 3 directives: iperf3s to start the
server, iperf3 to make a measurement and iperf3k to kill the server, so
that we can start the server less often.  This - and more importantly, the
reduced number of waits for the server to be ready - reduces runtime of the
performance tests on my laptop by about 4m (out of ~28minutes).

For now we still restart the server between IPv4 and IPv6 tests.  That's
because in some cases the latency measurements we make in between use the
same ports.

Signed-off-by: David Gibson 
Signed-off-by: Stefano Brivio

passt: Relicense to GPL 2.0, or any later version

2023-04-06T16:00:33+00:00

In practical terms, passt doesn't benefit from the additional
protection offered by the AGPL over the GPL, because it's not
suitable to be executed over a computer network.

Further, restricting the distribution under the version 3 of the GPL
wouldn't provide any practical advantage either, as long as the passt
codebase is concerned, and might cause unnecessary compatibility
dilemmas.

Change licensing terms to the GNU General Public License Version 2,
or any later version, with written permission from all current and
past contributors, namely: myself, David Gibson, Laine Stump, Andrea
Bolognani, Paul Holzinger, Richard W.M. Jones, Chris Kuhn, Florian
Weimer, Giuseppe Scrivano, Stefan Hajnoczi, and Vasiliy Ulyanov.

Signed-off-by: Stefano Brivio

test/perf: Finally drop workaround for virtio_net TX stall

2022-11-04T11:04:32+00:00

Now that we require 13c6be96618c ("net: stream: add unix socket")
in qemu to run the tests, we can also assume that commit df8d07081718
("virtio-net: fix bottom-half packet TX on asynchronous completion")
is present, as it was merged before that one.

This fixes the issue we attempted to work around in passt TCP and
UDP performance tests: finally drop that stuff.

Signed-off-by: Stefano Brivio

test/perf: Wait for neper servers in guest to be ready before starting client

2022-09-23T00:46:24+00:00

Starting tcp_rr, tcp_crr, udp_rr servers in the guest takes a bit
longer than starting the corresponding clients on the host, and we
end up starting clients before servers unless we add a delay there.

Signed-off-by: Stefano Brivio

test/perf: Disable periodic throughput reports to avoid vhost hang

2022-09-22T14:54:09+00:00

It appears that if we run throughput tests with one-second periodic
reports, the sending side of the vhost channel used for SSH-based
command dispatch occasionally stops working altogether. I haven't
investigated this further, all I see is that output is truncated
at some point, and doesn't resume.

If we use gzip compression (ssh -C) this happens less frequently,
but it still happens, seemingly indicating the issue is probably
related to vhost itself.

Disable periodic reports in iperf3 clients. The -i options were
actually redundant, so remove them from both test files as well as
from test_iperf3().

Signed-off-by: Stefano Brivio

test/perf: Switch performance test duration to 10 seconds instead of 30

2022-09-22T14:53:55+00:00

It looks like the workaround for the virtio_net TX hang issue is
working less reliably with the new command dispatch mechanism, I'm
not sure why. Switch to 10 seconds, at least for the moment.

Signed-off-by: Stefano Brivio 
Reviewed-by: David Gibson

test/perf: Always use /sbin/sysctl in tcp test

2022-09-22T14:53:35+00:00

Signed-off-by: Stefano Brivio 
Reviewed-by: David Gibson