* [Xenomai-core] TLB misses on MPC 8xx
@ 2005-10-19 19:56 Wolfgang Grandegger
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From: Wolfgang Grandegger @ 2005-10-19 19:56 UTC (permalink / raw)
To: xenomai
Hello,
the output of the cache calibrator indicated, that TLB misses on the MPC
860 might influence latencies substantially.
Looking closer to the Linux 2.6 kernel revealed, that TLB entries for
the kernel space (0xc0000000) are not pinned by default for the MPC 860
(like in 2.4). I enabled this advanced kernel option PIN_TLB and
furthermore patched the kernel to put modules in that kernel space by
using kmalloc instead of vmalloc. Then I get the following latency figures:
KLATENCY with load:
RTH|---lat min|---lat avg|---lat max|-overrun|--lat best|---lat worst
RTS| 50560| 98976| 199040| 0| 00:09:45
RTS| 50240| 89401| 174400| 0| 00:10:06 PIN_TLB
RTS| 48960| 85562| 164480| 0| 00:10:30 PIN_TLB+kmalloc
LATENCY with load:
RTH|---lat min|---lat avg|---lat max|-overrun|--lat best|---lat worst
RTS| 60480| 120960| 224320| 0| 00:09:46
RTS| 60800| 105600| 193600| 0| 00:09:56 PIN_TLB
RTS| 55680| 98240| 176640| 0| 00:15:01 PIN_TLB+kmalloc
This clearly shows, that TLB misses are one latency killer on low end
processors.
Wolfgang.
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2005-10-19 19:56 [Xenomai-core] TLB misses on MPC 8xx Wolfgang Grandegger
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