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Re: C3600 kernel/64bit 4.* slow IO due to -mlong-calls

Hi Carlo,

On 15.03.2018 16:36, Carlo Pisani wrote:
> I am experiencing a very annoying behavior with my HPPA C3600: if I
> compile the (linux) kernel with  -mlong-calls then the IO (e.g. file
> copy) becomes very slow, and the PCI becomes unstable (i.e. it crashes
> the machine)
> kernel  gcc     binutils    with mlong    without mlong
> 4.15.7  4.9.3   2.25.1     13.4 MB/s    27.0 MB/s
> 4.15.7  6.4.0   2.25.1     13.4 MB/s    27.0 MB/s
> 4.15.7  6.4.0   2.29.1     14.4 MB/s    25.0 MB/s

Interesting bad results!
> these tests were performed with
> dd if=/dev/zero of=here bs=1k count=100000
> -mlong-calls is enabled in the kernel by "CONFIG_MLONGCALLS"

I think nobody else noticed the bad performance due to CONFIG_MLONGCALLS yet.
I've now started some testing if we can disable that option on the debian

> the help-guide says "If you configure the kernel to include many
> drivers built-in instead as modules, the kernel executable may become
> too big, so that the linker will not be able to resolve some long
> branches and fails to link your vmlinux kernel. In that case enabling
> this option will help you to overcome this limit by using the
> -mlong-calls compiler option. Usually you want to say N here, unless
> you e.g. want to build a kernel which includes all necessary drivers
> built-in and which can be used for TFTP booting without the need to
> have an initrd ramdisk. Enabling this option will probably slow down
> your kernel"
> I need -mlong-calls because I need to compile the kernel without
> kernel-modules


> all built-in, that makes the size of the kernel of
> about 23Mbytes, thus without -mlong-calls the linker fails to "link"
> objects
> let me know

I'm not sure what kind of help you expect here?
The only option I see is that you try to disable some options (modules) you won't
need and thus reduce the kernel size. xfs, ipv6 and such are good candidates.
Or use a 32bit kernel ?


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