Messages in this thread | | | Subject | Re: [PATCH v2] sched/debug: Add new tracepoint to track cpu_capacity | From | Dietmar Eggemann <> | Date | Wed, 2 Sep 2020 12:44:42 +0200 |
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+ Phil Auld <pauld@redhat.com>
On 28/08/2020 19:26, Qais Yousef wrote: > On 08/28/20 19:10, Dietmar Eggemann wrote: >> On 28/08/2020 12:27, Qais Yousef wrote: >>> On 08/28/20 10:00, vincent.donnefort@arm.com wrote: >>>> From: Vincent Donnefort <vincent.donnefort@arm.com>
[...]
>> Can you remind me why we have all these helper functions like >> sched_trace_rq_cpu_capacity? > > struct rq is defined in kernel/sched/sched.h. It's not exported. Exporting > these helper functions was the agreement to help modules trace internal info. > By passing generic info you decouple the tracepoint from giving specific info > and allow the modules to extract all the info they need from the same > tracepoint. IE: if you need more than just cpu_capacity from this tracepoint, > you can get that without having to continuously add extra arguments everytime > you need an extra piece of info. Unless this info is not in the rq of course.
I think this decoupling is not necessary. The natural place for those scheduler trace_event based on trace_points extension files is kernel/sched/ and here the internal sched.h can just be included.
If someone really wants to build this as an out-of-tree module there is an easy way to make kernel/sched/sched.h visible.
CFLAGS_sched_tp.o := -I$KERNEL_SRC/kernel/sched
all: make -C $KERNEL_SRC M=$(PWD) modules
This allowed me to build our trace_event extension module (sched_tp.c, sched_events.h) out-of-tree and I was able to get rid of all the sched_trace_foo() functions (in fair.c, include/linux/sched.h) and code there content directly in foo.c
There are two things we would need exported from the kernel:
(1) cfs_rq_tg_path() to print the path of a taskgroup cfs_rq or se.
(2) sched_uclamp_used so uclamp_rq_util_with() can be used in sched_events.h.
I put Phil Auld on cc because of his trace_point sched_update_nr_running_tp. I think Phil was using sched_tp as a base so I can't see an issue why we can't also remove sched_trace_rq_nr_running().
>> In case we would let the extra code (which transforms trace points into >> trace events) know the internals of struct rq we could handle those >> things in the TRACE_EVENT and/or the register_trace_##name(void >> (*probe)(data_proto), void *data) thing. >> We always said when the internal things will change this extra code will >> break. So that's not an issue. > > The problem is that you need to export struct rq in a public header. Which we > don't want to do. I have been trying to find out how to use BTF so we can > remove these functions. Haven't gotten far away yet - but it should be doable > and it's a question of me finding enough time to understand what was currently > done and if I can re-use something or need to come up with extra infrastructure > first.
Let's keep the footprint of these trace points as small as possible in the scheduler code.
I'm putting the changes I described above in our monthly EAS integration right now and when this worked out nicely I will share the patches on lkml.
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