Messages in this thread | | | Date | Mon, 22 Jun 2020 13:17:47 +0100 | From | Qais Yousef <> | Subject | Re: [PATCH] Sched: Add a tracepoint to track rq->nr_running |
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On 06/19/20 10:11, Phil Auld wrote: > Add a bare tracepoint trace_sched_update_nr_running_tp which tracks > ->nr_running CPU's rq. This is used to accurately trace this data and > provide a visualization of scheduler imbalances in, for example, the > form of a heat map. The tracepoint is accessed by loading an external > kernel module. An example module (forked from Qais' module and including > the pelt related tracepoints) can be found at: > > https://github.com/auldp/tracepoints-helpers.git > > A script to turn the trace-cmd report output into a heatmap plot can be > found at: > > https://github.com/jirvoz/plot-nr-running > > The tracepoints are added to add_nr_running() and sub_nr_running() which > are in kernel/sched/sched.h. Since sched.h includes trace/events/tlb.h > via mmu_context.h we had to limit when CREATE_TRACE_POINTS is defined. > > Signed-off-by: Phil Auld <pauld@redhat.com> > CC: Qais Yousef <qais.yousef@arm.com> > CC: Ingo Molnar <mingo@redhat.com> > CC: Peter Zijlstra <peterz@infradead.org> > CC: Vincent Guittot <vincent.guittot@linaro.org> > CC: linux-kernel@vger.kernel.org > --- > include/trace/events/sched.h | 4 ++++ > kernel/sched/core.c | 9 ++++----- > kernel/sched/fair.c | 2 -- > kernel/sched/pelt.c | 2 -- > kernel/sched/sched.h | 12 ++++++++++++ > 5 files changed, 20 insertions(+), 9 deletions(-) > > diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h > index ed168b0e2c53..a6d9fe5a68cf 100644 > --- a/include/trace/events/sched.h > +++ b/include/trace/events/sched.h > @@ -634,6 +634,10 @@ DECLARE_TRACE(sched_overutilized_tp, > TP_PROTO(struct root_domain *rd, bool overutilized), > TP_ARGS(rd, overutilized)); > > +DECLARE_TRACE(sched_update_nr_running_tp, > + TP_PROTO(int cpu, int change, unsigned int nr_running), > + TP_ARGS(cpu, change, nr_running)); > + > #endif /* _TRACE_SCHED_H */ > > /* This part must be outside protection */ > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 9a2fbf98fd6f..6f28fdff1d48 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -6,7 +6,10 @@ > * > * Copyright (C) 1991-2002 Linus Torvalds > */ > + > +#define SCHED_CREATE_TRACE_POINTS > #include "sched.h" > +#undef SCHED_CREATE_TRACE_POINTS > > #include <linux/nospec.h> > > @@ -21,9 +24,6 @@ > > #include "pelt.h" > > -#define CREATE_TRACE_POINTS > -#include <trace/events/sched.h> > - > /* > * Export tracepoints that act as a bare tracehook (ie: have no trace event > * associated with them) to allow external modules to probe them. > @@ -34,6 +34,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_dl_tp); > EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_irq_tp); > EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_se_tp); > EXPORT_TRACEPOINT_SYMBOL_GPL(sched_overutilized_tp); > +EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp); > > DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues); > > @@ -7969,5 +7970,3 @@ const u32 sched_prio_to_wmult[40] = { > /* 10 */ 39045157, 49367440, 61356676, 76695844, 95443717, > /* 15 */ 119304647, 148102320, 186737708, 238609294, 286331153, > }; > - > -#undef CREATE_TRACE_POINTS > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index da3e5b54715b..fe5d9b6db8f7 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -22,8 +22,6 @@ > */ > #include "sched.h" > > -#include <trace/events/sched.h> > - > /* > * Targeted preemption latency for CPU-bound tasks: > * > diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c > index b647d04d9c8b..bb69a0ae8d6c 100644 > --- a/kernel/sched/pelt.c > +++ b/kernel/sched/pelt.c > @@ -28,8 +28,6 @@ > #include "sched.h" > #include "pelt.h" > > -#include <trace/events/sched.h> > - > /* > * Approximate: > * val * y^n, where y^32 ~= 0.5 (~1 scheduling period) > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index db3a57675ccf..6ae96679c169 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -75,6 +75,15 @@ > #include "cpupri.h" > #include "cpudeadline.h" > > +#ifdef SCHED_CREATE_TRACE_POINTS > +#define CREATE_TRACE_POINTS > +#endif > +#include <trace/events/sched.h> > + > +#ifdef SCHED_CREATE_TRACE_POINTS > +#undef CREATE_TRACE_POINTS > +#endif > + > #ifdef CONFIG_SCHED_DEBUG > # define SCHED_WARN_ON(x) WARN_ONCE(x, #x) > #else > @@ -1959,6 +1968,7 @@ static inline void add_nr_running(struct rq *rq, unsigned count) > unsigned prev_nr = rq->nr_running; > > rq->nr_running = prev_nr + count; > + trace_sched_update_nr_running_tp(cpu_of(rq), count, rq->nr_running);
This is a very specific call site, so I guess it looks fine to pass very specific info too.
But I think we can do better by just passing struct rq and add a new helper sched_trace_rq_nr_running() (see the bottom of fair.c for a similar helper functions for tracepoints).
This will allow the user to extract, cpu, nr_running and potentially other info while only pass a single argument to the tracepoint. Potentially extending its future usefulness.
The count can be inferred by storing the last nr_running and taking the diff when a new call happens.
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cpu = sched_trace_rq_cpu(rq); nr_running = sched_trace_rq_nr_running(rq); count = last_nr_running[cpu] - nr_running; last_nr_running[cpu] = nr_running;
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I haven't looked at BTF, but it could potentially allow us to access members of unexported structs reliably without having to export all these helper functions. It's been something I wanted to look into but no time yet.
Thanks
-- Qais Yousef
> > #ifdef CONFIG_SMP > if (prev_nr < 2 && rq->nr_running >= 2) { > @@ -1973,6 +1983,8 @@ static inline void add_nr_running(struct rq *rq, unsigned count) > static inline void sub_nr_running(struct rq *rq, unsigned count) > { > rq->nr_running -= count; > + trace_sched_update_nr_running_tp(cpu_of(rq), -count, rq->nr_running); > + > /* Check if we still need preemption */ > sched_update_tick_dependency(rq); > } > -- > 2.18.0 >
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