topic Re: Cache memory in Operating System - OpenVMS

Cache memory

Cache memory and VMS — Fri, 19 Jan 2007 08:22:24 GMT

Hi , Please can you tell us how to find out the processor cache in VMS . Which command to use ? show mem/cache shows the extended cache. is there a way to find the processor cache ?

regards
Anup

Re: Cache memory

Robert Gezelter — Fri, 19 Jan 2007 08:28:46 GMT

The Extended Cache is the File System Cache for data blocks. It is not a cache used by the CPU for shortening the time to get to memory.

The size of the hardware cache is a function of which CPU and CPU cards that your system has. This information is not, to the best of my recollection, available through the standard OpenVMS libraries.

What information soecifically are you looking for?

- Bob Gezelter, http://www.rlgsc.com

Re: Cache memory

Ian Miller. — Fri, 19 Jan 2007 08:34:49 GMT

statitics on the use of the CPU cache may be available via DCPI

See the following VTJ article for an intro
http://h71000.www7.hp.com/openvms/journal/v2/articles/dcpi.html

Are you after configuration information such as the amount of cache in the model of CPU?

For HP Integrity servers running VMS this is shown by the SHOW CPU command
e.g one of mine shows.
HP rx2620 (1.60GHz/6.0MB)

Re: Cache memory

Hein van den Heuvel — Fri, 19 Jan 2007 10:09:32 GMT

Just use $SHOW CPU [/FULL ] ?

$ show cpu/full
:
System: TD183, HP rx2600 (1.40GHz/1.5MB)
: ~~~~~~
:

Here (on OpenVMS Itanium 8.3) you see the system node name , the model, and (speed/cachesize).

If you need to know more, then tell us more!
What OS? What box? Why do you think you need to know? If you just pick e anoumber between 1 and 10 MB will those who want to know be happy and go away?
Basically, anyone who does nto know how to get the number also will not be able to to anything useful with the number. So fake it, or thell them 'irrelevant!'.

Good luck,
Hein.

Re: Cache memory

Cache memory and VMS — Fri, 19 Jan 2007 10:25:35 GMT

Hi ,
thanks a lot for the quick reply on my query . Well, this request came from my customer as they are building a DB of all this relevant and irrelevant informations. One of the question is to get the CPU cache size .

The box is a ES45 running OVMS7.3-1. As you mentioned show cpu/full is not giving the info for the Alpha system .

Thanks for suggesting DCPI, but I dont have the product installed now . And cant install now without approval from customer.

please let me know your thoughts ,

regards
Anup .

Re: Cache memory

Robert Gezelter — Fri, 19 Jan 2007 11:14:39 GMT

Anup,

For the actual cache size, you can check out the hardware configuration in the documentation.

- Bob Gezelter, http://www.rlgsc.com

Re: Cache memory

Hoff — Fri, 19 Jan 2007 11:29:51 GMT

The Alpha 21264 series EV6 processor has a so-called Harvard Architecture level one cache design used for its on-chip processor cache, with a 64 KB instruction cache and a 64 KB data cache.

The EV6 level one cache is set-associative, virtually indexed, physically tagged, and writeback.

The 1 GHz Alpha EV6 processor configurations within the AlphaServer ES45 series systems have an off-chip level two cache of 8 MB using 250 MHz DDR.

The 1.25 GHz Alpha EV6 processor configurations within the AlphaServer ES45 series systems have a level two off-chip cache of 16 MB using 313 MHz DDR.

The EV7-based AlphaServer ES47 series system has far smaller caches, but its caching efficiency and its cache performance is equivalent to that of the (far larger) cache found on the EV6-based AlphaServer ES45 EV6 series. And this is due in no small part to the significantly higher off-chip bandwidth of the EV7 series processor. EV7 bandwidth to local main memory is twice as fast as EV6 bandwidth to its level two processor cache.

In isolation, all discussions of processor cache size should be approached cautiously.

XFC and other OpenVMS system caches can be far, far, far larger. The above addresses the hardware caches found AlphaServer ES45 EV6-based systems.

Stephen Hoffman
HoffmanLabs

Re: Cache memory

Hein van den Heuvel — Fri, 19 Jan 2007 11:40:15 GMT

You can not buy you Alpha with different cache sizes, you would need to bu a different Aplha chip. So it seems to me that "N.A." would be a find entry into that table! Not Available / Not Applicable.

ANAL/SYSTEM.. CLUE CONFIG... will give you all CPU detail info available. For example:

"System Type AlphaServer DS20 500 MHz
Cycle Time 2.0 nsec (500 MHz)
:
CPU Type EV6 Pass 2.3 (21264)"

You'll need paper / web resoearch to map the 21264 to a cache size, or call it 1MB or "NA"

Hein.