On 07/09/12 15:28, Will Deacon wrote:
> On Thu, Sep 06, 2012 at 06:16:03PM +0100, Marc Zyngier wrote:
>> Add minimal guest support to perf, so it can distinguish whether
>> the PMU interrupt was in the host or the guest, as well as collecting
>> some very basic information (guest PC, user vs kernel mode).
>>
>> This is not feature complete though, as it doesn't support backtracing
>> in the guest.
>>
>> Based on the x86 implementation, tested with KVM/ARM.
>>
>> Cc: Will Deacon <will.deacon@xxxxxxx>
>> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
>> ---
>> arch/arm/include/asm/perf_event.h | 7 ++++++-
>> arch/arm/kernel/perf_event.c | 36 ++++++++++++++++++++++++++++++++++++
>> 2 files changed, 42 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/include/asm/perf_event.h b/arch/arm/include/asm/perf_event.h
>> index e074948..77537bb 100644
>> --- a/arch/arm/include/asm/perf_event.h
>> +++ b/arch/arm/include/asm/perf_event.h
>> @@ -12,6 +12,11 @@
>> #ifndef __ARM_PERF_EVENT_H__
>> #define __ARM_PERF_EVENT_H__
>>
>> -/* Nothing to see here... */
>> +/* Not much to see here... */
>
> You can just remove this silly comment :)
Now you're taking away the little fun I had hacking this. Life is soooo
cruel... ;-)
>> +struct pt_regs;
>> +extern unsigned long perf_instruction_pointer(struct pt_regs *regs);
>> +extern unsigned long perf_misc_flags(struct pt_regs *regs);
>> +#define perf_misc_flags(regs) perf_misc_flags(regs)
>>
>> #endif /* __ARM_PERF_EVENT_H__ */
>> diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
>> index ab243b8..8836425 100644
>> --- a/arch/arm/kernel/perf_event.c
>> +++ b/arch/arm/kernel/perf_event.c
>> @@ -817,6 +817,10 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
>> {
>> struct frame_tail __user *tail;
>>
>> + if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
>> + /* TODO: We don't support guest os callchain now */
>> + return;
>> + }
>>
>> tail = (struct frame_tail __user *)regs->ARM_fp - 1;
>>
>> @@ -844,9 +848,41 @@ perf_callchain_kernel(struct perf_callchain_entry *entry, struct pt_regs *regs)
>> {
>> struct stackframe fr;
>>
>> + if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
>> + /* TODO: We don't support guest os callchain now */
>> + return;
>> + }
>> +
>
> Will we ever support this? It sounds incredibly difficult -- how can you
> walk the guest stack without things disappearing under your feet?
It's hard, but not impossible:
- Stop the world (all vcpus)
- Repeatedly call into HYP mode to resolve all the VAs needed by the
backtrace (cringe...)
- Restart the world
- Witness your guest running at the speed of a snail lost in the Sahara.
I reckon it is a perfect project for a summer student! :-)
>> +unsigned long perf_instruction_pointer(struct pt_regs *regs)
>> +{
>> + if (perf_guest_cbs && perf_guest_cbs->is_in_guest())
>> + return perf_guest_cbs->get_guest_ip();
>> +
>> + return instruction_pointer(regs);
>> +}
>> +
>> +unsigned long perf_misc_flags(struct pt_regs *regs)
>> +{
>> + int misc = 0;
>> +
>> + if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
>> + if (perf_guest_cbs->is_user_mode())
>> + misc |= PERF_RECORD_MISC_GUEST_USER;
>> + else
>> + misc |= PERF_RECORD_MISC_GUEST_KERNEL;
>> + } else {
>> + if (user_mode(regs))
>> + misc |= PERF_RECORD_MISC_USER;
>> + else
>> + misc |= PERF_RECORD_MISC_KERNEL;
>> + }
>> +
>> + return misc;
>> +}
>
> Hmm, both of these look like they should be made generic but I see that x86
> and ppc do have some differences, so I guess we should have our own copies
> for the time being...
We can probably factor in the common code and let ARM use the default.
I'll have a look if I get a chance.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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