[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v6 16/18] vmx: Add some scheduler hooks for VT-d posted interrupts
>>> On 16.09.15 at 18:56, <George.Dunlap@xxxxxxxxxxxxx> wrote: > On Mon, Sep 7, 2015 at 1:54 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote: >>>>> On 25.08.15 at 03:57, <feng.wu@xxxxxxxxx> wrote: >>> --- a/xen/arch/x86/domain.c >>> +++ b/xen/arch/x86/domain.c >>> @@ -1573,6 +1573,22 @@ static void __context_switch(void) >>> per_cpu(curr_vcpu, cpu) = n; >>> } >>> >>> +static inline void pi_ctxt_switch_from(struct vcpu *prev) >>> +{ >>> + /* >>> + * When switching from non-idle to idle, we only do a lazy context >>> switch. >>> + * However, in order for posted interrupt (if available and enabled) to >>> + * work properly, we at least need to update the descriptors. >>> + */ >>> + if ( prev->arch.pi_ctxt_switch_from && !is_idle_vcpu(prev) ) >>> + prev->arch.pi_ctxt_switch_from(prev); >>> +} >>> + >>> +static inline void pi_ctxt_switch_to(struct vcpu *next) >>> +{ >>> + if ( next->arch.pi_ctxt_switch_to && !is_idle_vcpu(next) ) >>> + next->arch.pi_ctxt_switch_to(next); >>> +} >>> >>> void context_switch(struct vcpu *prev, struct vcpu *next) >>> { >>> @@ -1605,9 +1621,12 @@ void context_switch(struct vcpu *prev, struct vcpu >>> *next) >>> >>> set_current(next); >>> >>> + pi_ctxt_switch_from(prev); >>> + >>> if ( (per_cpu(curr_vcpu, cpu) == next) || >>> (is_idle_domain(nextd) && cpu_online(cpu)) ) >>> { >>> + pi_ctxt_switch_to(next); >>> local_irq_enable(); >> >> This placement, if really intended that way, needs explanation (in a >> comment) and perhaps even renaming of the involved symbols, as >> looking at it from a general perspective it seems wrong (with >> pi_ctxt_switch_to() excluding idle vCPU-s it effectively means you >> want this only when switching back to what got switched out lazily >> before, i.e. this would be not something to take place on an arbitrary >> context switch). As to possible alternative names - maybe make the >> hooks ctxt_switch_prepare() and ctxt_switch_cancel()? > > Why on earth is this more clear than what he had before? > > In the first call, he's not "preparing" anything -- he's actually > switching the PI context out for prev. And in the second call, he's > not "cancelling" anything -- he's actually switching the PI context in > for next. The names you suggest are actively confusing, not helpful. While I think later discussion on this thread moved in a good direction, I still think I should reply here (even if late): To me, the use of pi_ctxt_switch_to() in the patch fragment still seen above is very much the cancellation of the immediately preceding pi_ctxt_switch_from(), as it's the "we don't want to do anything else" path that it gets put into. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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