v2.6 performance slowdown on MPC8xx: Measuring TLB cache misses

Wolfgang Denk wd at denx.de
Mon Apr 25 06:59:40 EST 2005

Dear Marcelo,

thanks for starting this discussion, and for providing a patch for 8xx.

However, I think we should not only look at the TLB handling problems
on the 8xx processors. This is probably just a part of  the  problem.
In  general  the 2.6 performance on (small) embedded systems is much,
much worse than what we see with a 2.4 kernel.

I put some results (2.4.25 vs. on a MPC860 and on a MPC8240)
at http://www.denx.de/twiki/bin/view/Know/Linux24vs26

Here is the summary:

Using the 2.6 kernel on embedded  systems  implicates  the  following
* Slow to build: 2.6 takes 30...40% longer to compile
* Big memory footprint in flash: the 2.6 compressed kernel image is
  30...40% bigger
* Big memory footprint in RAM: the 2.6 kernel needs 30...40% more
  RAM; the available RAM size for applications is 700kB smaller
* Slow to boot: 2.6 takes 5...15% longer to boot into multi-user mode
* Slow to run: context switches up to 96% slower, local communication
  latencies up to 80% slower, file system latencies up to 76% slower,
  local communication bandwidth less than 50% in some cases.

It's a disappointing result, indeed.

Best regards,

Wolfgang Denk

Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
Another megabytes the dust.

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