[PATCH v3] Use the POWER8 Micro Partition Prefetch Engine in KVM HV on POWER8
stewart at linux.vnet.ibm.com
Fri Jul 18 14:10:14 EST 2014
Paul Mackerras <paulus at samba.org> writes:
> On Thu, Jul 17, 2014 at 01:19:57PM +1000, Stewart Smith wrote:
>> The POWER8 processor has a Micro Partition Prefetch Engine, which is
>> a fancy way of saying "has way to store and load contents of L2 or
>> L2+MRU way of L3 cache". We initiate the storing of the log (list of
>> addresses) using the logmpp instruction and start restore by writing
>> to a SPR.
>> The logmpp instruction takes parameters in a single 64bit register:
>> - starting address of the table to store log of L2/L2+L3 cache contents
>> - 32kb for L2
>> - 128kb for L2+L3
>> - Aligned relative to maximum size of the table (32kb or 128kb)
>> - Log control (no-op, L2 only, L2 and L3, abort logout)
>> We should abort any ongoing logging before initiating one.
> Do we ever want to wait for ongoing logging to finish?
*Probably* not... but as far as I can see the hardware doesn't expose a
way to find out if there is any ongoing logging or a way to be notified
when it's done.
>> +#if defined(CONFIG_PPC_64K_PAGES)
>> +#define MPP_BUFFER_ORDER 0
>> +#elif defined(CONFIG_PPC_4K_PAGES)
>> +#define MPP_BUFFER_ORDER 4
> Why 4 not 3? You only need 32kB, don't you?
>> +static struct kvmppc_vcore *kvmppc_vcore_create(struct kvm *kvm, int core)
>> + struct kvmppc_vcore *vcore;
>> + vcore = kzalloc(sizeof(struct kvmppc_vcore), GFP_KERNEL);
>> + if (vcore == NULL)
>> + return NULL;
>> + INIT_LIST_HEAD(&vcore->runnable_threads);
>> + spin_lock_init(&vcore->lock);
>> + init_waitqueue_head(&vcore->wq);
>> + vcore->preempt_tb = TB_NIL;
>> + vcore->lpcr = kvm->arch.lpcr;
>> + vcore->first_vcpuid = core * threads_per_core;
>> + vcore->kvm = kvm;
> Is there a particular reason why you need to pull this code out into a
> separate function? If so, it would be a little nicer if you did that
> in a separate patch, to make it easier to see that the code motion
> changes nothing.
>> @@ -1590,9 +1645,16 @@ static void kvmppc_run_core(struct kvmppc_vcore *vc)
>> srcu_idx = srcu_read_lock(&vc->kvm->srcu);
>> + if (vc->mpp_buffer_is_valid)
>> + ppc_start_restoring_l2_cache(vc);
>> + if (vc->mpp_buffer)
>> + ppc_start_saving_l2_cache(vc);
> I wonder if we would get better performance improvements if we kicked
> this off earlier, for instance before we save all the FP/VSX state and
> switch the MMU? I guess that could be a subsequent patch.
Possibly, yes. Maybe something to look at in future patch, along with if
also doing the L3 save/restore is a benefit.
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