tree 5ce12fc0676f93a49f743dab1c60f8e1ca991ec3
parent a32a8813d0173163ba44d8f9556e0d89fdc4fb46
author Rusty Russell <rusty@rustcorp.com.au> 1244867223 -0600
committer Rusty Russell <rusty@rustcorp.com.au> 1244811423 +0930

lguest: optimize by coding restore_flags and irq_enable in assembler.

The downside of the last patch which made restore_flags and irq_enable
check interrupts is that they are now too big to be patched directly
into the callsites, so the C versions are always used.

But the C versions go via PV_CALLEE_SAVE_REGS_THUNK which saves all
the registers.  In fact, we don't need any registers in the fast path,
so we can do better than this if we actually code them in assembler.

The results are in the noise, but since it's about the same amount of
code, it's worth applying.

1GB Guest->Host: input(suppressed),output(suppressed)
Before:
	Seconds: 0:16.53
	Packets: 377268,753673
	Interrupts: 22461,24297
	Notifications: 1(5245),21303(732370)
	Net IRQs triggered: 377023(245),42578(711095)

After:
	Seconds: 0:16.48
	Packets: 377289,753673
	Interrupts: 22281,24465
	Notifications: 1(5245),21296(732377)
	Net IRQs triggered: 377060(229),42564(711109)

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>