On Mon, Oct 27, 2014 at 1:32 PM, Preeti U Murthy
<preeti@xxxxxxxxxxxxxxxxxx> wrote:
> Hi Liu,
>
> On 10/17/2014 12:59 AM, kernelfans@xxxxxxxxx wrote:
>> Nowadays, powerKVM runs with secondary hwthread offline. Although
>> we can make all secondary hwthread online later, we still preserve
>> this behavior for dedicated KVM env. Achieve this by setting
>> paca->online as false.
>>
>> Signed-off-by: Liu Ping Fan <pingfank@xxxxxxxxxxxxxxxxxx>
>> ---
>> arch/powerpc/include/asm/paca.h | 3 +++
>> arch/powerpc/kernel/asm-offsets.c | 3 +++
>> arch/powerpc/kernel/smp.c | 3 +++
>> arch/powerpc/kvm/book3s_hv_rmhandlers.S | 12 ++++++++++++
>> 4 files changed, 21 insertions(+)
>>
>> diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
>> index a5139ea..67c2500 100644
>> --- a/arch/powerpc/include/asm/paca.h
>> +++ b/arch/powerpc/include/asm/paca.h
>> @@ -84,6 +84,9 @@ struct paca_struct {
>> u8 cpu_start; /* At startup, processor spins until */
>> /* this becomes non-zero. */
>> u8 kexec_state; /* set when kexec down has irqs off */
>> +#ifdef CONFIG_KVMPPC_ENABLE_SECONDARY
>> + u8 online;
>> +#endif
>> #ifdef CONFIG_PPC_STD_MMU_64
>> struct slb_shadow *slb_shadow_ptr;
>> struct dtl_entry *dispatch_log;
>> diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
>> index 9d7dede..0faa8fe 100644
>> --- a/arch/powerpc/kernel/asm-offsets.c
>> +++ b/arch/powerpc/kernel/asm-offsets.c
>> @@ -182,6 +182,9 @@ int main(void)
>> DEFINE(PACATOC, offsetof(struct paca_struct, kernel_toc));
>> DEFINE(PACAKBASE, offsetof(struct paca_struct, kernelbase));
>> DEFINE(PACAKMSR, offsetof(struct paca_struct, kernel_msr));
>> +#ifdef CONFIG_KVMPPC_ENABLE_SECONDARY
>> + DEFINE(PACAONLINE, offsetof(struct paca_struct, online));
>> +#endif
>> DEFINE(PACASOFTIRQEN, offsetof(struct paca_struct, soft_enabled));
>> DEFINE(PACAIRQHAPPENED, offsetof(struct paca_struct, irq_happened));
>> DEFINE(PACACONTEXTID, offsetof(struct paca_struct, context.id));
>> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
>> index a0738af..4c3843e 100644
>> --- a/arch/powerpc/kernel/smp.c
>> +++ b/arch/powerpc/kernel/smp.c
>> @@ -736,6 +736,9 @@ void start_secondary(void *unused)
>>
>> cpu_startup_entry(CPUHP_ONLINE);
>>
>> +#ifdef CONFIG_KVMPPC_ENABLE_SECONDARY
>> + get_paca()->online = true;
>> +#endif
>> BUG();
>> }
>>
>> diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> index f0c4db7..d5594b0 100644
>> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
>> @@ -322,6 +322,13 @@ kvm_no_guest:
>> li r0, KVM_HWTHREAD_IN_NAP
>> stb r0, HSTATE_HWTHREAD_STATE(r13)
>> kvm_do_nap:
>> +#ifdef PPCKVM_ENABLE_SECONDARY
>> + /* check the cpu is needed by host or not */
>> + ld r2, PACAONLINE(r13)
>> + ld r3, 0
>> + cmp r2, r3
>> + bne kvm_secondary_exit_trampoline
>> +#endif
>> /* Clear the runlatch bit before napping */
>> mfspr r2, SPRN_CTRLF
>> clrrdi r2, r2, 1
>> @@ -340,6 +347,11 @@ kvm_do_nap:
>> nap
>> b .
>>
>> +#ifdef PPCKVM_ENABLE_SECONDARY
>> +kvm_secondary_exit_trampoline:
>> + b .
>
> Uh? When we have no vcpu to run, we loop here instead of doing a nap?
> What are we achieving?
>
> If I understand the intention of the patch well, we are looking to
> provide a knob whereby the host can indicate if it needs the secondaries
> at all.
>
Yes, you catch it :)
> Today the host does boot with all threads online. There are some init
> scripts which take the secondaries down. So today the host does not have
> a say in preventing this, compile time or runtime. So lets see how we
> can switch between the two behaviors if we don't have the init script,
> which looks like a saner thing to do.
>
> We should set the paca->online flag to false by default. If
> KVM_PPC_ENABLE_SECONDARY is configured, we need to set this flag to
> true. So at compile time, we resolve the flag.
>
> While booting, we look at the flag and decide whether to get the
> secondaries online. So we get the current behavior if we have not
> configured KVM_PPC_ENABLE_SECONDARY. Will this achieve the purpose of
> this patch?
>
At boot time, KVM can not run. So we can achieve the change of the
flag by soft cpu hotplug on/off.
I think this is a more flexible way.
Thx,
Fan
> Regards
> Preeti U Murthy
>
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