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SubjectRE: [PATCH V2 1/6] perf,core: allow invalid context events to be part of sw/hw groups
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>
> On Wed, Apr 15, 2015 at 03:56:11AM -0400, Kan Liang wrote:
> > The event count only be read when the event is already sched_in.
>
> Yeah, so no. This breaks what groups are. Group events _must_ be co-
> scheduled. You cannot guarantee you can schedule events from another
> PMU.

Why? I think it's similar as sw and hw mixed event group.
group_sched_in will co-schedule all events in sibling_list.
Invalid context events is already added in sibling_list in
perf_install_in_context.
So all group events will be scheduled together.
event->pmu guarantee proper add is called.
For invalid context events, everything is global. It never fails to schedule.

>
> Also, I cannot see how this can possibly work, you cannot put these things
> on the same event_context.

Why not? For a sw and hw mixed event group, they use same
hw event_context.

Actually, the invalid context events don't have any state to switch
on context switch. They can attach to any event_context.

>
> Also, how does this work wrt cpumasks, regular events are per cpu, uncore
> events are per node.

Currently, uncore events is only available on the first cpu of the node.
So if it's a hw and uncore mixed group, only cpu 0 do the group.
For other CPUs, there will be only hw event.
Perf tool will guarantee it. Here are some examples.

[perf]$ sudo perf record -e '{cycles,uncore_imc_0/cas_count_read/}:S'
-C 0-4 -vvv -- sleep 1
------------------------------------------------------------
perf_event_attr:
size 112
{ sample_period, sample_freq } 4000
sample_type IP|TID|TIME|READ|ID|CPU|PERIOD
read_format ID|GROUP
disabled 1
mmap 1
comm 1
freq 1
task 1
sample_id_all 1
exclude_guest 1
mmap2 1
comm_exec 1
------------------------------------------------------------
sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8
sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8
sys_perf_event_open: pid -1 cpu 2 group_fd -1 flags 0x8
sys_perf_event_open: pid -1 cpu 3 group_fd -1 flags 0x8
sys_perf_event_open: pid -1 cpu 4 group_fd -1 flags 0x8
------------------------------------------------------------
perf_event_attr:
type 15
size 112
config 304
sample_type IP|TID|TIME|READ|ID|CPU|PERIOD
read_format ID|GROUP
freq 1
sample_id_all 1
exclude_guest 1
------------------------------------------------------------
sys_perf_event_open: pid -1 cpu 0 group_fd 3 flags 0x8
mmap size 528384B
perf event ring buffer mmapped per cpu



[perf]$ sudo perf stat -e '{cycles,uncore_imc_0/cas_count_read/}' -C 0-4
--per-core -- sleep 1

Performance counter stats for 'CPU(s) 0-4':

S0-C0 1 1367712 cycles (100.00%)
S0-C0 1 0.17 MiB uncore_imc_0/cas_count_read/
S0-C1 1 982923 cycles
S0-C1 0 <not counted> MiB uncore_imc_0/cas_count_read/
S0-C2 1 958585 cycles
S0-C2 0 <not counted> MiB uncore_imc_0/cas_count_read/
S0-C3 1 978161 cycles
S0-C3 0 <not counted> MiB uncore_imc_0/cas_count_read/
S0-C4 1 976012 cycles
S0-C4 0 <not counted> MiB uncore_imc_0/cas_count_read/

1.001151765 seconds time elapsed


>
> There is so much broken stuff here without explanation its not funny.
>
> Please explain how this does not completely wreck everything?

OK. I will refine the description when questions as above are addressed.

Thanks,
Kan


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