Re: crash in entry.S restore_all, 2.6.12-rc2, x86, PAGEALLOC

Ingo Molnar
2005-04-07T14:52:08Z

* Linus Torvalds <torvalds@osdl.org> wrote:

> > > pushfl

> After all, I very strongly suspect that we don't actually really
> _care_ if eflags stays the same over a system call, and I could see
> that some dynamic CPU's might prefer not having to push an eflags
> value that just got changed by the "sti", so it _might_ save several
> cycles to avoid that dependency, and also obviously avoid a subtle
> dependency on a sw level that the previous patch clearly introduced.
>
> Anybody willing to time it? ;)

i can tell you without any measurement that pushfl is slower by a couple
of cycles than a simple pushl $0x00010046, on basically all x86 CPUs.
And since we only support SYENTER from 32-bit mode and we dont guarantee
flags to be saved, it isnt all that incorrect to do?

Ingo