Describe the per-target token bucket and the two configfs files that drive it: ratelimit_interval_ms and ratelimit_burst.
Spell out the two properties that are not obvious from the file names. The limit is accounted per message rather than per packet, so a message split into several ncfrag packets is never truncated by the bucket running dry halfway through. Signed-off-by: Breno Leitao <[email protected]> --- Documentation/networking/netconsole.rst | 43 +++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/Documentation/networking/netconsole.rst b/Documentation/networking/netconsole.rst index 4ab5d7b05cf10..7369cd89ae76c 100644 --- a/Documentation/networking/netconsole.rst +++ b/Documentation/networking/netconsole.rst @@ -177,6 +177,49 @@ You can modify these targets in runtime by creating the following targets:: cat cmdline1/remote_ip 10.0.0.3 +Rate limiting +------------- + +Netconsole hands every console message to every enabled target, so a host that +logs continuously can saturate the receiving agent. Each target carries a token +bucket that drops messages once the configured rate is exceeded, controlled by +two files in the target directory: + + ===================== ================================================ + ratelimit_interval_ms Length of the accounting interval, in + milliseconds. Zero, the default, sends + everything. + ratelimit_burst Messages allowed per interval. Defaults to + 10; zero drops every message. + ===================== ================================================ + +Unlike most target parameters, both knobs can be written while the target is +enabled, which is when a flooding target most likely needs them. + +The limit is applied per message, not per packet, so a message big enough to be +split into several `ncfrag` packets is either sent whole or not at all. + +Crash output bypasses the bucket. While an oops, BUG() or panic() is in +progress every message is sent, whatever the limit says, so a small burst +cannot cost you part of a crash dump. + +A drop leaves nothing on the wire, so the receiver is told what it missed as +soon as a message gets through again:: + + netconsole: 45 messages dropped by rate limit + +The notice only travels with the next message the bucket allows. A host that +goes quiet right after being limited reports the drops later, when it logs +again, and a target with a `ratelimit_burst` of zero never reports them. + +netconsole generates the notice itself instead of logging it, so on an +extended target the record carries a sequence number of zero. + +Capping a target at 500 messages a minute:: + + echo 60000 > ratelimit_interval_ms + echo 500 > ratelimit_burst + Append User Data ---------------- -- 2.53.0-Meta
