Messages in this thread | | | Date | Tue, 08 Sep 2015 10:45:47 +0900 | From | AKASHI Takahiro <> | Subject | Re: [PATCH] arm64: kernel: Use a separate stack for irq interrupts. |
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Jungseok,
On 09/08/2015 01:34 AM, Jungseok Lee wrote: > On Sep 8, 2015, at 1:06 AM, James Morse wrote: >> On 07/09/15 16:48, Jungseok Lee wrote: >>> On Sep 7, 2015, at 11:36 PM, James Morse wrote: >>> >>> Hi James, >>> >>>> Having to handle interrupts on top of an existing kernel stack means the >>>> kernel stack must be large enough to accomodate both the maximum kernel >>>> usage, and the maximum irq handler usage. Switching to a different stack >>>> when processing irqs allows us to make the stack size smaller. >>>> >>>> Maximum kernel stack usage (running ltp and generating usb+ethernet >>>> interrupts) was 7256 bytes. With this patch, the same workload gives >>>> a maximum stack usage of 5816 bytes. >>> >>> I'd like to know how to measure the max stack depth. >>> AFAIK, a stack tracer on ftrace does not work well. Did you dump a stack >>> region and find or track down an untouched region? >> >> I enabled the 'Trace max stack' option under menuconfig 'Kernel Hacking' -> >> 'Tracers', then looked in debugfs:/tracing/stack_max_size. >> >> What problems did you encounter? >> (I may be missing something…) > > When I enabled the feature, all entries had *0* size except the last entry. > It can be reproduced easily as looking in debugs:/tracing/stack_trace.
I'm afraid that you have not applied one of patches in my RFC: http://lists.infradead.org/pipermail/linux-arm-kernel/2015-July/355919.html
I have not looked into James' patch in details, but hope that it will help fix one of issues that are annoying me: Stack tracer (actually save_stack_trace()) will miss a function (and its parent function in some case) that is being executed when an interrupt is taken.
-Takahiro AKASHI
> You can track down my report and Akashi's changes with the following links: > - http://lists.infradead.org/pipermail/linux-arm-kernel/2015-July/354126.html > - https://lkml.org/lkml/2015/7/13/29 > > Although it is impossible to measure an exact depth at this moment, the feature > could be utilized to check improvement. > > Cc'ing Akashi for additional comments if needed. > > Best Regards > Jungseok Lee >
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