Messages in this thread | | | Date | Tue, 16 Nov 1999 13:08:24 -0500 | From | Josip Loncaric <> | Subject | DRAM thermal throttling by 440BX chipset |
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The 440BX motherboard chipset can block DRAM read/write accesses under certain conditions. This behavior is not under direct CPU control, and it may have unintended consequences, particularly where device drivers are concerned. On our system, some DRAM writes may be delayed by almost 20 microseconds, which may explain why sometimes I/O instructions can overtake writes to RAM.
For example, on our system the motherboard chipset counts DRAM writes over a window of one second. When more than 213065 QWords are written during that second, the 440BX chipset starts a throttle monitoring window. After 627 QWords are written during this period, further write requests are blocked for the remainder of this 20 microsecond window. This monitoring is repeated for over a minute. Reads are handled similarly.
Thanks to a code segment by Robert Redelmeier, I managed to examine the 440BX chipset registers which control the DRAM read/write thermal throttling behavior. Here is my interpretation of the results obtained using our ASUS P2B-DS motherboards (BIOS 1009, Linux Kernel 2.2.13, dual Pentium III 500MHz):
DWTC: 80003e8f 7fffb39c Throttle Lock ON: DWTC is read-only Global DRAM Write Sampling Window: 1000 milliseconds Global QWord Threshold: 213065 QWords per 1000ms Throttle Time: 63000 milliseconds Throttle Monitoring Window: 2000 DRAM CLKs Throttle QWord Maximum: 627 QWords in 2000 DRAM CLKs while throttling
DRTC: 00003e9d cff7d32c Throttle Lock ON: DRTC is read-only Global DRAM Read Sampling Window: 1000 milliseconds Global Read QWord Threshold: 189845 QWords per 1000ms Read Throttle Time: 63000 milliseconds Read Throttle Monitoring Window: 992 DRAM CLKs Read Throttle QWord Maximum: 613 QWords in 992 DRAM CLKs while throttling
Our other ASUS motherboards (P2B and P2B-D) are similar except that some have a bit lower threshold values.
Sincerely, Josip
-- Dr. Josip Loncaric, Senior Staff Scientist mailto:josip@icase.edu ICASE, Mail Stop 132C http://www.icase.edu/~josip/ NASA Langley Research Center mailto:j.loncaric@larc.nasa.gov Hampton, VA 23681-2199, USA Tel. +1 757 864-2192 Fax +1 757 864-6134
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