* Jeremy Fitzhardinge <[email protected]> wrote:
> > Eric's test shows a 5% slowdown. That's far from cheap.
>
> It seems like an absurdly large difference. PDA references aren't all
> that common in the kernel; for the %gs prefix on PDA accesses to be
> causing a 5% overall difference in a test like this means that the
> prefixes would have to be costing hundreds or thousands of cycles,
> which seems absurd. Particularly since Eric's patch doesn't touch
> head.S, so the %gs save/restore is still being executed.
i said this before: using segmentation tricks these days is /insane/.
Segmentation is not for free, and it's not going to be cheap in the
future. In fact, chances are that it will be /more/ expensive in the
future, because sane OSs just make no use of them besides the trivial
"they dont even exist" uses.
so /at a minimum/, as i suggested it before, the kernel's segment use
should not overlap that of glibc's. I.e. the kernel should use %fs, not
%gs.
Ingo
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
