On 16.02.2012, at 18:28, Scott Wood wrote: > On 02/16/2012 11:18 AM, Alexander Graf wrote: >> >> On 16.02.2012, at 17:58, Scott Wood wrote: >> >>> On 02/16/2012 04:24 AM, Alexander Graf wrote: >>>> On 16.02.2012, at 10:26, Liu Yu <yu.liu@xxxxxxxxxxxxx> wrote: >>>>> +_GLOBAL(epapr_ev_idle) >>>>> +epapr_ev_idle: >>>>> + rlwinm r3,r1,0,0,31-THREAD_SHIFT /* current thread_info */ >>>>> + lwz r4,TI_LOCAL_FLAGS(r3) /* set napping bit */ >>>>> + ori r4,r4,_TLF_NAPPING /* so when we take an exception */ >>>>> + stw r4,TI_LOCAL_FLAGS(r3) /* it will return to our caller */ >>>>> + >>>>> + wrteei 1 >>>>> + >>>>> +idle_loop: >>>>> + LOAD_REG_IMMEDIATE(r11, HC_VENDOR_EPAPR | HC_EV_IDLE) >>>>> + >>>>> +.global epapr_ev_idle_start >>>>> +epapr_ev_idle_start: >>>>> + li r3, -1 >>>>> + nop >>>>> + nop >>>>> + nop >>>> >>>> Can't you just bl into epapr_hypercall_start? You don't even have to save the old lr. because we never return anyways :) >>> >>> The interrupt will branch to LR, so no, we can't trash it or put it >>> anywhere else. >> >> Hrm. But we can clobber ctr, right? So how about we make the generic version do a bctr and then just do a small C wrapper that takes lr, moves it to ctr and branches to the generic one? > > If it's just for this, I would say don't mess with the normal hcall path > for the sake of idle. If using CTR would let us get away without > creating a stack frame in call sites, maybe that would be worthwhile, > depending on what sort of hcalls we end up having. > >> Then we don't have to replicate the hypercall code all over again for every invocation. > > We shouldn't need to do it for every invocation. Idle is special due to > the TLF_NAPPING hack. Famous last words. If it's the only case, duplication should be ok. Let's hope there are no others. Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
