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Re: Stack usage measurement
- From: Szentirmai Gergely <reg at t-online dot hu>
- To: Gary Thomas <gary at mlbassoc dot com>, eCos Discuss <ecos-discuss at ecos dot sourceware dot org>
- Date: Mon, 20 Apr 2009 10:39:16 +0200
- Subject: Re: [ECOS] Stack usage measurement
- References: <49EB78F3.email@example.com> <49EB7B23.firstname.lastname@example.org>
Gary Thomas írta:
Szentirmai Gergely wrote:
I had a bad feeling about stack usage (perhaps measurement), and I have
written a small testcode, to see what's really happening. It came with
an interesting result. It seems to me, that cyg_thread_info.stack_used
gives the max used stack size, not the actual. Is that right? According
to the docs, it should give the current usage.
The test code is attached, I use arm-elf-gcc, ecos with default packages.
The result is also attached. I think that even the last stack usage
should be equal with 144 Bytes.
Maybe I am wrong... maybe not.
No, you are correct, the value is the maximum used. Why is this
less useful than the 'current' used? Stacks aren't reused or
dynamic (they don't grow or shrink), so [IMO] the most useful
measurement is the max size you'll ever need, which is the
measured value [at the time of the measurement, of course]
I agree with you, but I was interrested about the current usage in this
case. I thought that the difference between cyg_thread_info.stack_used
(CYGFUN_KERNEL_THREADS_STACK_MEASUREMENT enabled) is exactly this
(current vs max usage). If both measure the max usage, than what is the
difference? cyg_thread_measure_stack_usage is just a shortcut to the same?
In addition, every call your code makes to 'diag_printf()'
perturbs the measurement, as it can use a lot of stack itself!
If you want to be very pure about the measurements, save the
stack information in some variables and only print the results
when done, that way 'diag_printf()'s use won't get in the way.
This is one of the things why I would like to measure the current usage.
I have tried to minimize this effect by avoid any %d and use
diag_write_dec(info.stack_used); So diag_printf only have to push the
My initialization thread now use 3k+ stack, which is way to much (I
have 32k of SRAM) from a simple initialization thread. I think
"printf-s" has a big part in it (trace, log etc.).
Does anybody has a estimation about the stack usage of pintf stuff? I
think it should use about the length of the printed text, and some more
because of the calling parameters. I know that it is depending on the
As a summary, I would have to avoid the usage of any printf if I'm short
In this case I would implement a stack usage optimalized printf
(statically allocated (or malloc) working buffer) for debugging purpose.
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