Re: 2.6.18-rc6-mm1: GPF loop on early boot

Jeremy Fitzhardinge
2006-09-11T08:13:33Z

Ingo Molnar wrote:
> the ratio between the number of syscalls vs. the number of context
> switches is 1-2 orders of magnitude. So a loss of 9 cycles in the
> syscall path is roughly equal to a loss of 90-900 cycles in switch_to()
> costs ...
>

I agree.

> the TLS ABI is just a gcc stupidity. Why did they pick the _second_
> extra selector, instead of the first one ...?

Well, it doesn't matter which they chose if its the same for user and
kernel space. Why does x86-64 have swapgs rather than swapfs?

> Anyway, perhaps this could
> be solved by extending gcc with a switch to also generate __thread code
> off %fs. Probably not worth the pain though ...

If there's gcc hacking to be done, it would be trying to get it make the
TLS offsets from the PDA/TCB positive rather than negative...

J