RE: [ECOS] Massive ISR to DSR delay caused by free()

[Bernd Edlinger <bernd.edlinger@hotmail.de>]

On Tue, 3 Dec 2013 11:19:17, Peter Graf wrote:
>
> Hi,
>
> under rare circumstances, we experienced a massive timing overflow of a cyclical DSR. It turned out to be an issue with JFFS2, occurring after a system reboot if long files had been written to the filesystem before.
>
> I found that the issue was only caused by JFFS2's
>
> malloc-ecos.c: jffs2_free_full_dnode()
>
> By using an oscilloscope, I could see that after the ISR was served, the DSR was delayed, just because free() was called by jffs2_free_full_dnode(). More precisely, the CPU time was spent in memalloc's
>
> mvarimpl.inl: Cyg_Mempool_Variable_Implementation::insert_free_block()
>
> At first I thought it was a locking issue within JFFS2. But in the end I could not see any scheduler locks which might have caused it.
>
> I now have indications, that it could be a general issue with free(). A call to free() from even a low priority thread seems to delay DSR execution after the ISR!
>
> The allocator is compiled to be thread-safe, but in my opinion it would be a major drawback if even a low priority thread could not call free() without delaying a critical DSR.
>
> Can someone confirm this behaviour? Is it intended?
>
> Many thanks,
> Peter
>
>
>
>
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>

This sounds like a know deficiency of the very first Doug-Lee Malloc.

Maybe you want check if this patch works for you?

http://bugs.ecos.sourceware.org/show_bug.cgi?id=1001634


Regards
Bernd Edlinger. 		 	   		  
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