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The counters, the phase hooks in idle() and the "health" command are now behind HEALTH, set from the command line with HEALTH=1. Without it the hooks are empty macros and the command does not exist, so a default build carries none of it: on SWTGW218AS that is 1065 bytes of bank 2, 101 of the common segment and 28 of xdata, plus seven banked calls per main-loop pass. It is a developer's tool. Reading the dump takes knowing the main loop, and a user who needs it for a report can build with the flag on, which is how the kernel treats its lock and latency instrumentation as well.
80 lines
3.2 KiB
Markdown
80 lines
3.2 KiB
Markdown
# The health command
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`health` prints a one-page snapshot of the firmware's vital signs on the
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serial console. It exists for the situations where the switch misbehaves and
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every probe from the network measures the network instead of the device: the
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dump is taken from inside, costs one command, and works while HTTP does not.
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```
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> health
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up 0000001f ticks 0x00001f4c loops 0x000016da rx 0x024e
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link max 01 slow 0x0000
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sfp max 74 slow 0x0001
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rx max 00 slow 0x0000
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tx max 00 slow 0x0000
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stp max 04 slow 0x0001
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cmd max 02 slow 0x0001
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sp 80 untouched 62
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tcp st 00 tmr 00 rtx 00 rto 00 len 0x0000 mss 0x05b4
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lport 0x0000 rport 0x0000 rip 0x0000 0x0000
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httpd left 0x0000 entry 00 stp 01 mvlan 0x0002
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```
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The instrumentation is not part of a default build. It costs about 1.1 kB
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of bank 2, a few bytes of xdata and seven banked calls per main-loop pass,
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which is nothing a user needs unless they are chasing a problem, so it is
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switched on at build time:
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```
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make MACHINE=SWTGW218AS HEALTH=1
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```
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Without it the hooks compile to nothing and `health` is not a command.
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All figures are raw hex. The counters are cumulative: take two dumps a known
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time apart and the differences give the rates.
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## The first line
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`up` is the seconds counter, `ticks` the system tick (200 per second),
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`loops` the number of main-loop passes and `rx` the frames handle_rx has
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taken off the NIC. A healthy loop completes one pass per tick, so the
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difference in `loops` tracks the difference in `ticks`; a loop that falls
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behind is being held up by one of the phases below. The `rx` rate separates
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a flooded CPU port from a stalled loop, which look identical from outside.
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## Phases
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Each line is one section of the main loop: the link poll, SFP handling,
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frame reception, TCP transmission, the STP timers and the command dispatch.
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`max` is the worst time that section has taken, in ticks of 5 ms; `slow`
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counts the passes that took two ticks or more. A misbehaving subsystem
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names itself here, which is the difference between knowing that the loop is
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slow and knowing why.
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A dump of its own output takes the console some milliseconds, so running
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`health` repeatedly increments the `cmd` counters by itself. That is the
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instrument observing itself, not a fault.
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## Stack
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At boot the free stack area is painted with a pattern. `sp` is the live
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stack pointer; `untouched` counts the painted bytes still intact at the top,
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which is the closest thing to a high-water mark this hardware offers. A
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shrinking `untouched` across dumps means something is reaching deeper than
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anything before it.
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## The TCP slot
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The connection table is printed whole, one slot per pair of lines: TCP
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state (3 is ESTABLISHED, 0 closed), retransmission timer and counter, bytes
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in flight, negotiated MSS, then the ports and the peer address. With a
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single slot serving the entire web interface, one glance answers the
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question every management outage starts with: who is holding it. A slot
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showing state 3 with nothing in flight and a peer that no longer answers is
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a connection whose owner went away.
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`httpd left` and `entry` describe the file transfer the web server believes
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it is in the middle of, and the trailing flags show whether STP is running
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and which VLAN carries management.
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