git: 6fa041d7f125 - main - Measure latency of PMC interruptions
Mateusz Guzik
mjguzik at gmail.com
Mon Sep 13 08:01:43 UTC 2021
On 9/13/21, Wojciech Macek <wma at freebsd.org> wrote:
> The branch main has been updated by wma:
>
> URL:
> https://cgit.FreeBSD.org/src/commit/?id=6fa041d7f125db65f400af7f520a41ff78d19cd7
>
> commit 6fa041d7f125db65f400af7f520a41ff78d19cd7
> Author: Wojciech Macek <wma at FreeBSD.org>
> AuthorDate: 2021-09-13 04:08:32 +0000
> Commit: Wojciech Macek <wma at FreeBSD.org>
> CommitDate: 2021-09-13 04:08:32 +0000
>
> Measure latency of PMC interruptions
>
> Add HWPMC events to measure latency.
> Provide sysctl to choose the number of outstanding events which
> trigger HWPMC event.
>
> Obtained from: Semihalf
> Sponsored by: Stormshield
> Differential revision: https://reviews.freebsd.org/D31283
> ---
> sys/kern/kern_intr.c | 58
> ++++++++++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 52 insertions(+), 6 deletions(-)
>
> diff --git a/sys/kern/kern_intr.c b/sys/kern/kern_intr.c
> index 1660414a50ef..19401877dfbd 100644
> --- a/sys/kern/kern_intr.c
> +++ b/sys/kern/kern_intr.c
> @@ -30,6 +30,7 @@
> __FBSDID("$FreeBSD$");
>
> #include "opt_ddb.h"
> +#include "opt_hwpmc_hooks.h"
> #include "opt_kstack_usage_prof.h"
>
> #include <sys/param.h>
> @@ -75,6 +76,7 @@ struct intr_thread {
> struct thread *it_thread; /* Kernel thread. */
> int it_flags; /* (j) IT_* flags. */
> int it_need; /* Needs service. */
> + int it_waiting; /* Waiting in the runq. */
> };
>
> /* Interrupt thread flags kept in it_flags */
> @@ -100,13 +102,19 @@ SYSCTL_INT(_hw, OID_AUTO, intr_storm_threshold,
> CTLFLAG_RWTUN,
> static int intr_epoch_batch = 1000;
> SYSCTL_INT(_hw, OID_AUTO, intr_epoch_batch, CTLFLAG_RWTUN,
> &intr_epoch_batch,
> 0, "Maximum interrupt handler executions without re-entering
> epoch(9)");
> +#ifdef HWPMC_HOOKS
> +static int intr_hwpmc_waiting_report_threshold = 1;
> +SYSCTL_INT(_hw, OID_AUTO, intr_hwpmc_waiting_report_threshold,
> CTLFLAG_RWTUN,
> + &intr_hwpmc_waiting_report_threshold, 1,
> + "Threshold for reporting number of events in a workq");
> +#endif
> static TAILQ_HEAD(, intr_event) event_list =
> TAILQ_HEAD_INITIALIZER(event_list);
> static struct mtx event_lock;
> MTX_SYSINIT(intr_event_list, &event_lock, "intr event list", MTX_DEF);
>
> static void intr_event_update(struct intr_event *ie);
> -static int intr_event_schedule_thread(struct intr_event *ie);
> +static int intr_event_schedule_thread(struct intr_event *ie, struct
> trapframe *frame);
> static struct intr_thread *ithread_create(const char *name);
> static void ithread_destroy(struct intr_thread *ithread);
> static void ithread_execute_handlers(struct proc *p,
> @@ -115,6 +123,16 @@ static void ithread_loop(void *);
> static void ithread_update(struct intr_thread *ithd);
> static void start_softintr(void *);
>
> +#ifdef HWPMC_HOOKS
> +#include <sys/pmckern.h>
> +PMC_SOFT_DEFINE( , , intr, all);
> +PMC_SOFT_DEFINE( , , intr, ithread);
> +PMC_SOFT_DEFINE( , , intr, filter);
> +PMC_SOFT_DEFINE( , , intr, stray);
> +PMC_SOFT_DEFINE( , , intr, schedule);
> +PMC_SOFT_DEFINE( , , intr, waiting);
> +#endif
> +
> /* Map an interrupt type to an ithread priority. */
> u_char
> intr_priority(enum intr_type flags)
> @@ -773,7 +791,7 @@ intr_handler_barrier(struct intr_handler *handler)
> }
> if ((handler->ih_flags & IH_CHANGED) == 0) {
> handler->ih_flags |= IH_CHANGED;
> - intr_event_schedule_thread(ie);
> + intr_event_schedule_thread(ie, NULL);
> }
> while ((handler->ih_flags & IH_CHANGED) != 0)
> msleep(handler, &ie->ie_lock, 0, "ih_barr", 0);
> @@ -872,7 +890,7 @@ intr_event_remove_handler(void *cookie)
> KASSERT((handler->ih_flags & IH_DEAD) == 0,
> ("duplicate handle remove"));
> handler->ih_flags |= IH_DEAD;
> - intr_event_schedule_thread(ie);
> + intr_event_schedule_thread(ie, NULL);
> while (handler->ih_flags & IH_DEAD)
> msleep(handler, &ie->ie_lock, 0, "iev_rmh", 0);
> intr_event_update(ie);
> @@ -944,7 +962,7 @@ intr_event_resume_handler(void *cookie)
> }
>
> static int
> -intr_event_schedule_thread(struct intr_event *ie)
> +intr_event_schedule_thread(struct intr_event *ie, struct trapframe *frame)
> {
> struct intr_entropy entropy;
> struct intr_thread *it;
> @@ -986,11 +1004,28 @@ intr_event_schedule_thread(struct intr_event *ie)
> atomic_store_rel_int(&it->it_need, 1);
> thread_lock(td);
> if (TD_AWAITING_INTR(td)) {
> +#ifdef HWPMC_HOOKS
> + atomic_set_int(&it->it_waiting, 0);
atomic_set does not assign the passed value, it or's it.
> + if (frame != NULL)
> + PMC_SOFT_CALL_TF( , , intr, schedule, frame);
> + else
> + PMC_SOFT_CALL( , , intr, schedule);
> +#endif
> CTR3(KTR_INTR, "%s: schedule pid %d (%s)", __func__, td->td_proc->p_pid,
> td->td_name);
> TD_CLR_IWAIT(td);
> sched_add(td, SRQ_INTR);
> } else {
> +#ifdef HWPMC_HOOKS
> + atomic_add_int(&it->it_waiting, 1);
Why is this using atomics to begin with? To my reading the field is de
facto protected by thread lock, so you can just it->it_waiting++
> +
> + if (atomic_load_int(&it->it_waiting) >=
> intr_hwpmc_waiting_report_threshold) {
The option is enabled by default but hwpmc itself is rarely loaded.
Then this avoidable loads intr_hwpmc_waiting_report_threshold to begin
with. Instead you can do something in the lines:
#define PMC_HOOK_INSTALLED_ANY() __predict_false(pmc_hook != NULL)
and use that to guard the other branches. Later on this will be hot
patchable so it wont be a problem by default.
> + if (frame != NULL)
> + PMC_SOFT_CALL_TF( , , intr, waiting, frame);
> + else
> + PMC_SOFT_CALL( , , intr, waiting);
> + }
> +#endif
> CTR5(KTR_INTR, "%s: pid %d (%s): it_need %d, state %d",
> __func__, td->td_proc->p_pid, td->td_name, it->it_need,
> TD_GET_STATE(td));
> thread_unlock(td);
> @@ -1083,7 +1118,7 @@ swi_sched(void *cookie, int flags)
> #endif
> } else {
> VM_CNT_INC(v_soft);
> - error = intr_event_schedule_thread(ie);
> + error = intr_event_schedule_thread(ie, NULL);
> KASSERT(error == 0, ("stray software interrupt"));
> }
> }
> @@ -1374,12 +1409,23 @@ intr_event_handle(struct intr_event *ie, struct
> trapframe *frame)
> ret = ih->ih_filter(frame);
> else
> ret = ih->ih_filter(ih->ih_argument);
> +#ifdef HWPMC_HOOKS
> + PMC_SOFT_CALL_TF( , , intr, all, frame);
> +#endif
> KASSERT(ret == FILTER_STRAY ||
> ((ret & (FILTER_SCHEDULE_THREAD | FILTER_HANDLED)) != 0 &&
> (ret & ~(FILTER_SCHEDULE_THREAD | FILTER_HANDLED)) == 0),
> ("%s: incorrect return value %#x from %s", __func__, ret,
> ih->ih_name));
> filter = filter || ret == FILTER_HANDLED;
> +#ifdef HWPMC_HOOKS
> + if (ret & FILTER_SCHEDULE_THREAD)
> + PMC_SOFT_CALL_TF( , , intr, ithread, frame);
> + else if (ret & FILTER_HANDLED)
> + PMC_SOFT_CALL_TF( , , intr, filter, frame);
> + else if (ret == FILTER_STRAY)
> + PMC_SOFT_CALL_TF( , , intr, stray, frame);
> +#endif
>
> /*
> * Wrapper handler special handling:
> @@ -1416,7 +1462,7 @@ intr_event_handle(struct intr_event *ie, struct
> trapframe *frame)
> if (thread) {
> int error __unused;
>
> - error = intr_event_schedule_thread(ie);
> + error = intr_event_schedule_thread(ie, frame);
> KASSERT(error == 0, ("bad stray interrupt"));
> }
> critical_exit();
>
--
Mateusz Guzik <mjguzik gmail.com>
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