Re: [RFC/INCOMPLETE 08/13] x86/entry/64: Migrate 64-bit syscalls to new exit hooks

[Ingo Molnar]

* Ingo Molnar <mingo@xxxxxxxxxx> wrote:

> 
> * Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> 
> > >> Any reason why irq state tracking cannot be done in C as well, like the 
> > >> rest of the irq state tracking code?
> > >
> > > Never mind, I see you've done exactly that in patch #12.
> > 
> > There are still some TRACE_IRQS_ON, LOCKDEP_SYS_EXIT, and such scattered 
> > throughout the asm.  it's plausible that even more of that could be moved to 
> > C.
> > 
> > We could also benchmark and find out how bad it would be if we just always 
> > filled pt_regs in completely in syscalls.  If the performance hit isn't enough 
> > to matter, then we could potentially move the entire syscall path except 
> > pt_regs setup and sysret/iret into three C functions.
> 
> The thing is, I'd not be against simplifying pt_regs handling even if it slows 
> down things a tiny bit. If anyone wants to reintroduce that complexity we'll see 
> how it looks like in isolation, done cleanly.

... and I suspect the reduction of entry points will allow the compiler to do a 
better job - so some of the overhead might be won back.

So I'd say we try this approach and complicate it back in the future only if the 
numbers warrant it.

Thanks,

	Ingo
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