Messages in this thread |  | | Subject | Re: [PATCH RFC 4/5] x86,fpu: lazily skip FPU restore when still loaded | From | Rik van Riel <> | Date | Mon, 03 Oct 2016 16:22:51 -0400 |
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On Mon, 2016-10-03 at 13:04 -0700, Dave Hansen wrote: > On 10/01/2016 01:31 PM, riel@redhat.com wrote: > > > > /* > > + * Check whether an FPU's register set is still loaded in the CPU. > > + */ > > +static inline bool fpu_lazy_skip_restore(struct fpu *fpu) > > +{ > > + bool still_loaded = (fpu->fpstate_active && > > + fpu->last_cpu == > > raw_smp_processor_id() && > > + __this_cpu_read(fpu_fpregs_owner_ctx) > > == fpu); > > + > > + fpu->fpregs_active = still_loaded; > > + return still_loaded; > > +} > I wonder if we should call this something more along the lines of > fpregs_activate_fast(), which returns if it managed to do the > activation > fast or not. I _think_ that's more along the lines of what it is > actually doing. The fact that it can be lazy is really an > implementation detail. > > What are the preempt rules with this thing? This needs to be called > in > preempt-disabled contexts, right?
Indeed, all the FPU context switching code needs to be called in preempt-disabled contexts.
You do not want to get preempted halfway through saving or restoring floating point registers.
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