This patchset uses eBPF perf-event based notification mechanism to solve
the problem described in
https://marc.info/?l=linux-netdev&m=154022219423571&w=2.
Thanks to Daniel Borkmann for feedback/input.
The problem statement is
We would like to monitor some subset of TCP sockets in user-space,
(the monitoring application would define 4-tuples it wants to monitor)
using TCP_INFO stats to analyze reported problems. The idea is to
use those stats to see where the bottlenecks are likely to be ("is it
application-limited?" or "is there evidence of BufferBloat in the
path?" etc)
Today we can do this by periodically polling for tcp_info, but this
could be made more efficient if the kernel would asynchronously
notify the application via tcp_info when some "interesting"
thresholds (e.g., "RTT variance > X", or "total_retrans > Y" etc)
are reached. And to make this effective, it is better if
we could apply the threshold check *before* constructing the
tcp_info netlink notification, so that we don't waste resources
constructing notifications that will be discarded by the filter.
This patchset solves the problem by adding perf-event based notification
support for sock_ops (Patch1). The eBPF kernel module can thus
be designed to apply any desired filters to the bpf_sock_ops and
trigger a perf-event notification based on the verdict from the filter.
The uspace component can use these perf-event notifications to either
read any state managed by the eBPF kernel module, or issue a TCP_INFO
netlink call if desired.
Patch 2 provides a simple example that shows how to use this infra
(and also provides a test case for it)
Sowmini Varadhan (2):
bpf: add perf-event notificaton support for sock_ops
selftests/bpf: add a test case for sock_ops perf-event notification
net/core/filter.c | 19 ++
tools/testing/selftests/bpf/Makefile | 4 +-
tools/testing/selftests/bpf/perf-sys.h | 74 ++++++++
tools/testing/selftests/bpf/test_tcpnotify.h | 19 ++
tools/testing/selftests/bpf/test_tcpnotify_kern.c | 95 +++++++++++
tools/testing/selftests/bpf/test_tcpnotify_user.c | 186 +++++++++++++++++++++
6 files changed, 396 insertions(+), 1 deletions(-)
create mode 100644 tools/testing/selftests/bpf/perf-sys.h
create mode 100644 tools/testing/selftests/bpf/test_tcpnotify.h
create mode 100644 tools/testing/selftests/bpf/test_tcpnotify_kern.c
create mode 100644 tools/testing/selftests/bpf/test_tcpnotify_user.c
