On Tue, Jan 21, 2014 at 5:07 PM, Liu ping fan <kernelfans@xxxxxxxxx> wrote: > On Tue, Jan 21, 2014 at 11:40 AM, Aneesh Kumar K.V > <aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote: >> Liu ping fan <kernelfans@xxxxxxxxx> writes: >> >>> On Mon, Jan 20, 2014 at 11:45 PM, Aneesh Kumar K.V >>> <aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote: >>>> Liu ping fan <kernelfans@xxxxxxxxx> writes: >>>> >>>>> On Thu, Jan 9, 2014 at 8:08 PM, Alexander Graf <agraf@xxxxxxx> wrote: >>>>>> >>>>>> On 11.12.2013, at 09:47, Liu Ping Fan <kernelfans@xxxxxxxxx> wrote: >>>>>> >>>>>>> This series is based on Aneesh's series "[PATCH -V2 0/5] powerpc: mm: Numa faults support for ppc64" >>>>>>> >>>>>>> For this series, I apply the same idea from the previous thread "[PATCH 0/3] optimize for powerpc _PAGE_NUMA" >>>>>>> (for which, I still try to get a machine to show nums) >>>>>>> >>>>>>> But for this series, I think that I have a good justification -- the fact of heavy cost when switching context between guest and host, >>>>>>> which is well known. >>>>>> >>>>>> This cover letter isn't really telling me anything. Please put a proper description of what you're trying to achieve, why you're trying to achieve what you're trying and convince your readers that it's a good idea to do it the way you do it. >>>>>> >>>>> Sorry for the unclear message. After introducing the _PAGE_NUMA, >>>>> kvmppc_do_h_enter() can not fill up the hpte for guest. Instead, it >>>>> should rely on host's kvmppc_book3s_hv_page_fault() to call >>>>> do_numa_page() to do the numa fault check. This incurs the overhead >>>>> when exiting from rmode to vmode. My idea is that in >>>>> kvmppc_do_h_enter(), we do a quick check, if the page is right placed, >>>>> there is no need to exit to vmode (i.e saving htab, slab switching) >>>> >>>> Can you explain more. Are we looking at hcall from guest and >>>> hypervisor handling them in real mode ? If so why would guest issue a >>>> hcall on a pte entry that have PAGE_NUMA set. Or is this about >>>> hypervisor handling a missing hpte, because of host swapping this page >>>> out ? In that case how we end up in h_enter ? IIUC for that case we >>>> should get to kvmppc_hpte_hv_fault. >>>> >>> After setting _PAGE_NUMA, we should flush out all hptes both in host's >>> htab and guest's. So when guest tries to access memory, host finds >>> that there is not hpte ready for guest in guest's htab. And host >>> should raise dsi to guest. >> >> Now guest receive that fault, removes the PAGE_NUMA bit and do an >> hpte_insert. So before we do an hpte_insert (or H_ENTER) we should have >> cleared PAGE_NUMA bit. >> >>>This incurs that guest ends up in h_enter. >>> And you can see in current code, we also try this quick path firstly. >>> Only if fail, we will resort to slow path -- kvmppc_hpte_hv_fault. >> >> hmm ? hpte_hv_fault is the hypervisor handling the fault. >> > After we discuss in irc. I think we should also do the fast check in > kvmppc_hpte_hv_fault() for the case of HPTE_V_ABSENT, > and let H_ENTER take care of the rest case i.e. no hpte when pte_mknuma. Right? > Or we can delay the quick fix in H_ENTER, and let the host fault again, so do the fix in kvmppc_hpte_hv_fault() > Thanks and regards, > Fan >> -aneesh >> -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
