On 01/07/2019 10:22 PM, Liang, Kan wrote:
Thanks for sharing. I understand the point of maintaining those
models at one place,
but this factor-out doesn't seem very elegant to me, like below
__intel_pmu_init (int model, struct x86_pmu *x86_pmu)
{
...
switch (model)
case INTEL_FAM6_NEHALEM:
case INTEL_FAM6_NEHALEM_EP:
case INTEL_FAM6_NEHALEM_EX:
intel_pmu_lbr_init(x86_pmu);
if (model != boot_cpu_data.x86_model)
return;
/* Other a lot of things init like below..*/
memcpy(hw_cache_event_ids, nehalem_hw_cache_event_ids,
sizeof(hw_cache_event_ids));
memcpy(hw_cache_extra_regs, nehalem_hw_cache_extra_regs,
sizeof(hw_cache_extra_regs));
x86_pmu.event_constraints = intel_nehalem_event_constraints;
x86_pmu.pebs_constraints =
intel_nehalem_pebs_event_constraints;
x86_pmu.enable_all = intel_pmu_nhm_enable_all;
x86_pmu.extra_regs = intel_nehalem_extra_regs;
...
Case...
}
We need insert "if (model != boot_cpu_data.x86_model)" in every "Case
xx".
What would be the rationale that we only do lbr_init for "x86_pmu"
when model != boot_cpu_data.x86_model?
(It looks more like a workaround to factor-out the function and get
what we want)
I thought the new function may be extended to support fake pmu as below.
It's not only for lbr. PMU has many CPU specific features. It can be
used for other features, if you want to check the compatibility in
future. But I don't have an example now.
__intel_pmu_init (int model, struct x86_pmu *x86_pmu)
{
bool fake_pmu = (model != boot_cpu_data.x86_model) ? true : false;
...
switch (model)
case INTEL_FAM6_NEHALEM:
case INTEL_FAM6_NEHALEM_EP:
case INTEL_FAM6_NEHALEM_EX:
intel_pmu_lbr_init(x86_pmu);
x86_pmu->event_constraints = intel_nehalem_event_constraints;
x86_pmu->pebs_constraints = intel_nehalem_pebs_event_constraints;
x86_pmu->enable_all = intel_pmu_nhm_enable_all;
x86_pmu->extra_regs = intel_nehalem_extra_regs;
if (fake_pmu)
return;
It looks similar as the one I shared above, the difference is that more
things
(e.g. constraints) are assigned to x86_fake_pmu.
I'm not sure about the logic behind it (still look like a workaround).
/* Global variables should not be updated for fake PMU */
memcpy(hw_cache_event_ids, nehalem_hw_cache_event_ids,
sizeof(hw_cache_event_ids));
memcpy(hw_cache_extra_regs, nehalem_hw_cache_extra_regs,
sizeof(hw_cache_extra_regs));
I would prefer having them separated as this patch for now - it is
logically more clear to me.
But it will be a problem for maintenance. Perf developer probably
forget to update the list in KVM. I think you have to regularly check
the perf code.
It's been very common in hypervisor development. That's why we have
hypervisor developers here.
When a new platform is added, we will definitely get some work like this
to do.
Best,
Wei
