Conference vaxaxp::alphanotes

49.0. "OpenVMS AXP CPU tick" by HGOVC::STEVENCHEUNG () Fri Feb 21 1997 01:14

	Dear ALL,	


	Lately I have a client who decided to re-write one of
	the macro programs of accessing the CPU null time 
	using Pascal under the Alpha Migration project.

	In the process of testing, errors was discovered that
	one of the displaying function of the CPU utilization
	is never/rarely displayed on AXP platform. In fact,
	however, the same code is working on the VAX side.

	The original macro program was written to access 
	the primary CPU data block using a pointer named
	SMP$GL_CPU_DATA. Having located the primary CPU
	data block, another offset named CPU$Q_NULLCPU
	is used to access the null ( idle ) time recorded
	for this primary CPU. In VAX side, the time was
	measured in 10-millisecond, however, on the Alpha
	platform, this was not the same case because the
	customer had written a Pascal program to access the
	SMP$GL_CPU_DATA data block directly. The values 
	obtained through tracing through the pascal program 
	showed the values obtained by many calls to the 
	CPU$Q_NULLCPU of each CPU data block, the figures 
	are much bigger than what was expected on the VAX 
	side. The unit of time used for this direct access
	may not be measured in 10-millisecond on the AXP
	platform. 


	My question at this point is :

	What is the unit used in this CPU$Q_NULLCPU of this
	CPU data block ? Is the measurement still in 
	10-millisecond unit or much smaller ?


	Please respond if you have any idea because this is
	rather crucial at this stage when the whole Migration
	can be completed with the correct displaying under the
	performance and integrity testing which are underway 
	before the customer can announce the launch date.

	It would mean the customer will start buying Alpha
	in tons and be the base of every system from now
	on and with years to come. 
	
	steve

   See the *GETSPI* keyword over in NOTED::HACKERS for a program that
   allows a user-mode program to retrieve null time using (undocumented)
   calls underneath MONITOR.

	The size of a tick is not constant.  Newer Alphas may use a different
	clock rate.  Instead of hardcoding 1024, use the contents of the system
	cell EXE$GL_SYSTICK, which is the size of a clock tick in 100ns units.

	-Dave

If this customer spends any time with privileged code, he or she should get a
copy of the Internals and Data Structures manual.  A few minutes in chapter 12
would have answered this question easily.

John