K 10
svn:author
V 5
luigi
K 8
svn:date
V 27
2002-06-30T07:56:49.000000Z
K 7
svn:log
V 1473
Add one function and one macro to timestamp events in the kernel using
the TSC register and which are just too conveninent not to have them around.

The macro (defined in sys/i386/include/param.h) is called

	TSTMP(class:4, unit:4, event:8, par:16)

which in turn calls _TSTMP(arg) (function defined in sys/i386/isa/clock.c)
which stores a pair of u_int32_t values <timestamp, arg> in a circular
buffer exported to userland as the sysctl variable debug.timestamp

The content of the buffer can be printed with something like

	sysctl -b debug.timestamp | hexdump -e '"%15u %15u\n"'

This functionality must be enabled with "options KERN_TIMESTAMP", otherwise
both the macro and the function are redefined as empty blocks.

This code is i586+ specific, but it does not make any attempt to grab
locks, identify which CPU it is running on, etc. etc. -- it is a debugging
tool, and a very very simple and low level one, so you are supposed to
know how to use it if you do not want to get random numbers out of it.

I am committing this to RELENG_4 only because on -current parts of
the kernel might run concurrently, so the use of a single unprotected
static variable as the index of the next entry in the buffer might
lead to inconsistent results. Plus, there might be similar stuff
in -current already.

If someone feels like porting this code to -current, it might be
a good idea to keep separate per-cpu buffers to avoid the cost
of protecting against concurrent accesses.

END