On Monday 07 August 2006 22:51, Zachary Amsden wrote: > Rusty Russell wrote: > >>> + > >>> +/* > >>> + * Set IOPL bits in EFLAGS from given mask > >>> + */ > >>> +static inline void set_iopl_mask(unsigned mask) > >>> > >> This function can be completely written in C using local_save_flags()/local_restore_flags() > >> Please do that. I guess it's still a good idea to keep it separated > >> though because it might allow other optimizations. > >> > >> e.g. i've been thinking about special casing IF changes in save/restore flags > >> to optimize CPUs which have slow pushf/popf. If you already make sure > >> all non IF manipulations of flags are separated that would help. > >> > > > Actually, that is not quite true. Local_save_flags / > raw_local_irq_restore today is used only for operating on IF flag, and > raw_local_restore_flags does not exist. Yes, sorry for the typo. > Our implementation of these in > VMI assumes that only the IF flag is being changed, and this is the > default assumption under which Xen runs as well. Using local_restore to > switch IOPL as well causes the extremely performance critical common > case of pure IRQ restore to do potentially a lot more work in a hypervisor. > > So if you do want us to go with the C approach, I would propose using > raw_local_iopl_restore, which can make a different hypercall (actually, > in our case, this is not even a hypercall, merely a VMI call). I meant Rusty can use local restore in his native implementation. The higher level interface can be different. -Andi
