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Date: Wed, 6 Mar 2024 16:38:17 +0000
From: Mark Rutland <mark.rutland@....com>
To: "JiaLong.Yang" <jialong.yang@...ngroup.cn>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf/core: Handle generic events normally instead of
trying all pmu
On Wed, Mar 06, 2024 at 11:10:15PM +0800, JiaLong.Yang wrote:
> We have pay more effort on handling generic events. We treat them
> specially caused us paying more.
Are you seeing an actual problem in practice? ... or is this just intended as a
cleanup/improvement?
What problem are you actually trying to solve here?
> Now time have told us that PMU type between 0 and PERF_TYPE_MAX only
> corresponds to one PMU.
There can be at most one PMU registered for each type, but several PMUs may
need to handle events for that type.
Trivially, there are a number of PMUs which share the PERF_TYPE_SOFTWARE type,
e.g.
* perf_swevent, handled by perf_swevent_init()
* perf_cpu_clock, handled by cpu_clock_event_init()
* perf_task_clock, handled by task_clock_event_init()
.. which have non-overlapping events in the PERF_TYPE_SOFTWARE event
namespace.
On systems with heterogeneous PMUs (e.g. ARM big.LITTLE systems), several PMUs
can handle the PERF_TYPE_{HARDWARE,RAW,CACHE} event namespaces, and there's
existing software that depends upon that working *without* the extended HW type
IDs.
> So we can handle the special when registering PMU not in event opening. And
> we can know which PMU is used to the generic event.
No we cannot. There may be several PMUs which need to handle a given generic
event type.
> The added capabilities PERF_PMU_CAP_EVENT_HARDWARE and
> PERF_PMU_CAP_EVENT_HW_CACHE will alloc idr for PERF_TYPE_HARDWARE and
> PERF_TYPE_HW_CACHE with same PMU.
When I suggested using capabilities in:
https://lore.kernel.org/lkml/ZecStMBA4YgQaBEZ@FVFF77S0Q05N/
.. I had meant that the core code could check just before calling the
pmu::event_init() function, in order to simplify the implementation of the
event_init() functions. I did not mean for this to change the way we
manipulated the IDR.
> We'd better handle uncore-task event before calling pmu->event_init().
This is a nice-to-have, but it's logically separate from the rest of this
patch.
>
> The code is compatible with PERF_PMU_TYPE_SHIFT.
> /*
> * attr.config layout for type PERF_TYPE_HARDWARE and PERF_TYPE_HW_CACHE
> * PERF_TYPE_HARDWARE: 0xEEEEEEEE000000AA
> * AA: hardware event ID
> * EEEEEEEE: PMU type ID
> * PERF_TYPE_HW_CACHE: 0xEEEEEEEE00DDCCBB
> * BB: hardware cache ID
> * CC: hardware cache op ID
> * DD: hardware cache op result ID
> * EEEEEEEE: PMU type ID
> * If the PMU type ID is 0, the PERF_TYPE_RAW will be applied.
> */
>
> But the drivers have to give the corresponding capabilities obviously.
>
> Signed-off-by: JiaLong.Yang <jialong.yang@...ngroup.cn>
> ---
> include/linux/perf_event.h | 4 +-
> kernel/events/core.c | 83 +++++++++++++++++++++++---------------
> 2 files changed, 54 insertions(+), 33 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index d2a15c0c6f8a..edf4365ab7cc 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -290,7 +290,9 @@ struct perf_event_pmu_context;
> #define PERF_PMU_CAP_ITRACE 0x0020
> #define PERF_PMU_CAP_NO_EXCLUDE 0x0040
> #define PERF_PMU_CAP_AUX_OUTPUT 0x0080
> -#define PERF_PMU_CAP_EXTENDED_HW_TYPE 0x0100
> +#define PERF_PMU_CAP_EVENT_HARDWARE 0x0100
> +#define PERF_PMU_CAP_EVENT_HW_CACHE 0x0200
> +#define PERF_PMU_CAP_EXTENDED_HW_TYPE 0x0300
>
> struct perf_output_handle;
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index f0f0f71213a1..02f14ae09d09 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -11516,6 +11516,7 @@ static struct lock_class_key cpuctx_lock;
> int perf_pmu_register(struct pmu *pmu, const char *name, int type)
> {
> int cpu, ret, max = PERF_TYPE_MAX;
> + int cap = pmu->capabilities;
>
> mutex_lock(&pmus_lock);
> ret = -ENOMEM;
> @@ -11523,7 +11524,6 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type)
> if (!pmu->pmu_disable_count)
> goto unlock;
>
> - pmu->type = -1;
> if (WARN_ONCE(!name, "Can not register anonymous pmu.\n")) {
> ret = -EINVAL;
> goto free_pdc;
> @@ -11538,15 +11538,34 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type)
> if (ret < 0)
> goto free_pdc;
>
> + /*
> + * Ensure one type ([0, PERF_TYPE_MAX)) correspond to one PMU.
> + */
> WARN_ON(type >= 0 && ret != type);
>
> type = ret;
> pmu->type = type;
>
> + if ((type != PERF_TYPE_HARDWARE) &&
> + (cap & PERF_PMU_CAP_EVENT_HARDWARE)) {
> + ret = idr_alloc(&pmu_idr, pmu, PERF_TYPE_HARDWARE,
> + PERF_TYPE_HARDWARE + 1, GFP_KERNEL);
> + if (ret < 0)
> + goto free_idr;
> + }
This means that if I try to register more than one PMU with
PERF_PMU_CAP_EVENT_HARDWARE, the second will fail IDR allocation and fail to
register.
.. so this is entirely useless for systems with heterogeneous PMUs, where each
of those *should* be able to handle plain PERF_TYPE_HARDWARE events for legacy reasons.
I agree that the existing event initialization code is grotty, but that's
largely an artifact of maintaining existing ABI. AFAICT this patch breaks that,
and makes the code complex in a different way rather than actually simlifying anything.
Therefore, NAK to this patch.
As above, I think it does make sense to have the core code own some common
checks (e.g. rejecting task-bound uncore events, filting generic events from
PMUs that don't support those), so I'm open to patches doing that.
Mark.
> +
> + if ((type != PERF_TYPE_HW_CACHE) &&
> + (cap & PERF_PMU_CAP_EVENT_HW_CACHE)) {
> + ret = idr_alloc(&pmu_idr, pmu, PERF_TYPE_HW_CACHE,
> + PERF_TYPE_HW_CACHE + 1, GFP_KERNEL);
> + if (ret < 0)
> + goto free_idr_hw;
> + }
> +
> if (pmu_bus_running && !pmu->dev) {
> ret = pmu_dev_alloc(pmu);
> if (ret)
> - goto free_idr;
> + goto free_idr_hw_cache;
> }
>
> ret = -ENOMEM;
> @@ -11604,6 +11623,14 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type)
> put_device(pmu->dev);
> }
>
> +free_idr_hw_cache:
> + if (cap & PERF_PMU_CAP_EVENT_HW_CACHE)
> + idr_remove(&pmu_idr, PERF_TYPE_HW_CACHE);
> +
> +free_idr_hw:
> + if (cap & PERF_PMU_CAP_EVENT_HARDWARE)
> + idr_remove(&pmu_idr, PERF_TYPE_HARDWARE);
> +
> free_idr:
> idr_remove(&pmu_idr, pmu->type);
>
> @@ -11648,6 +11675,7 @@ static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
> {
> struct perf_event_context *ctx = NULL;
> int ret;
> + bool uncore_pmu = false, extded_pmu = false;
>
> if (!try_module_get(pmu->module))
> return -ENODEV;
> @@ -11668,6 +11696,20 @@ static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
> BUG_ON(!ctx);
> }
>
> + if (perf_invalid_context == pmu->task_ctx_nr)
> + uncore_pmu = true;
> +
> + if (pmu->capabilities & PERF_PMU_CAP_EXTENDED_HW_TYPE)
> + extded_pmu = true;
> +
> + /* Disallow uncore-task events. */
> + if (uncore_pmu && (event->attach_state & PERF_ATTACH_TASK))
> + return -EINVAL;
> +
> + /* Ensure pmu not supporting generic events will not be passed such event. */
> + if (!extded_pmu && (event->attr.type & PERF_PMU_CAP_EXTENDED_HW_TYPE))
> + return -EINVAL;
> +
> event->pmu = pmu;
> ret = pmu->event_init(event);
>
> @@ -11695,7 +11737,6 @@ static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
>
> static struct pmu *perf_init_event(struct perf_event *event)
> {
> - bool extended_type = false;
> int idx, type, ret;
> struct pmu *pmu;
>
> @@ -11720,36 +11761,15 @@ static struct pmu *perf_init_event(struct perf_event *event)
> * are often aliases for PERF_TYPE_RAW.
> */
> type = event->attr.type;
> - if (type == PERF_TYPE_HARDWARE || type == PERF_TYPE_HW_CACHE) {
> - type = event->attr.config >> PERF_PMU_TYPE_SHIFT;
> - if (!type) {
> - type = PERF_TYPE_RAW;
> - } else {
> - extended_type = true;
> - event->attr.config &= PERF_HW_EVENT_MASK;
> - }
> - }
> + if (type == PERF_TYPE_HARDWARE || type == PERF_TYPE_HW_CACHE)
> + event->attr.config &= PERF_HW_EVENT_MASK;
>
> -again:
> rcu_read_lock();
> pmu = idr_find(&pmu_idr, type);
> rcu_read_unlock();
> - if (pmu) {
> - if (event->attr.type != type && type != PERF_TYPE_RAW &&
> - !(pmu->capabilities & PERF_PMU_CAP_EXTENDED_HW_TYPE))
> - goto fail;
>
> - ret = perf_try_init_event(pmu, event);
> - if (ret == -ENOENT && event->attr.type != type && !extended_type) {
> - type = event->attr.type;
> - goto again;
> - }
> -
> - if (ret)
> - pmu = ERR_PTR(ret);
> -
> - goto unlock;
> - }
> + if (!pmu || perf_try_init_event(pmu, event))
> + goto fail;
>
> list_for_each_entry_rcu(pmu, &pmus, entry, lockdep_is_held(&pmus_srcu)) {
> ret = perf_try_init_event(pmu, event);
> @@ -12026,11 +12046,10 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
> }
>
> /*
> - * Disallow uncore-task events. Similarly, disallow uncore-cgroup
> - * events (they don't make sense as the cgroup will be different
> - * on other CPUs in the uncore mask).
> + * Disallow uncore-cgroup events (they don't make sense
> + * as the cgroup will be different on other CPUs in the uncore mask).
> */
> - if (pmu->task_ctx_nr == perf_invalid_context && (task || cgroup_fd != -1)) {
> + if (task || cgroup_fd != -1) {
> err = -EINVAL;
> goto err_pmu;
> }
> --
> 2.25.1
>
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