On Fri, 5 Oct 2007, Franck Bui-Huu wrote:
> Maciej W. Rozycki wrote:
> > On Thu, 4 Oct 2007, Franck Bui-Huu wrote:
> >
> >> It's just a bit sad to see my TLB handler generated at each boot and
> >> to embed the whole tlbex generator inside the kernel which is quite
> >> big:
> >>
> >> $ mipsel-linux-size arch/mips/mm/tlbex.o
> >> text data bss dec hex filename
> >> 10116 3904 1568 15588 3ce4 arch/mips/mm/tlbex.o
> >>
> >> specially if my cpu doesn't have any bugs.
> >
> > Well, most systems are there to work and not to be rebooted repeatedly
> > all the time. ;-) All of tlbex.o is discarded after bootstrap.
> >
>
> Yes, but some systems out there have some constraints on their boot time
> and others have ones on their persistent storage device size.
>
> >> Maybe having, 2 default implementations in tlbex-r3k.S, tlbex-r4k.S
> >> for good cpus (the ones which needn't any fixups at all) and otherwise
> >> the tlbex.c is used. And with luck the majority of the cpus are
> >> good...
> >
> > Well, most of the differences are not due to CPU bugs, but different cp0
> > hazards. The MIPS32r2 and MIPS64r2 architecture specs introduce the "ehb"
> > and "jr.hb" instructions to sort them out, but most of the processors we
> > support predate them.
> >
> > The existence of the definitions in <asm/war.h> is there so that
> > workarounds for CPU bugs are optimised away at the kernel build time if
> > not activated.
>
> Just to be sure I haven't missed anything, it seems that we _could_ generate
> the whole tlb handler at compile time since the CPU type is known at that
> time, no need to have any fixups at runtime, isn't it ?
For specialized systems, you can always introduce the option to generate
the TLB handler at compile time:
- Enhance tlbex.c to be able to compile it for the host, and generate
a fixed TLB handler, based on CONFIG_* options, if
CONFIG_STATIC_TLB_HANDLER (buried deep in depends on EMBEDDED &&
ADVANCED && I_KNOW_WHAT_I_AM_DOING) is set.
- Let the dynamic runtime generator print the required CONFIG_*
options for the system it runs on, so you know which one to set in
your .config (a bit like calibrate_delay() prints the lpj=N value to
pass to avoid calibrating the delay loop)
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
