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Message-ID: <aICYAqM5EQUlTqtX@li-2b55cdcc-350b-11b2-a85c-a78bff51fc11.ibm.com>
Date: Wed, 23 Jul 2025 10:06:26 +0200
From: Sumanth Korikkar <sumanthk@...ux.ibm.com>
To: kan.liang@...ux.intel.com
Cc: peterz@...radead.org, mingo@...hat.com, namhyung@...nel.org,
irogers@...gle.com, mark.rutland@....com, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org, eranian@...gle.com,
ctshao@...gle.com, tmricht@...ux.ibm.com, leo.yan@....com,
linux-s390@...r.kernel.org
Subject: Re: [PATCH V4 07/16] s390/perf: Remove driver-specific throttle
support
On Tue, May 20, 2025 at 11:16:35AM -0700, kan.liang@...ux.intel.com wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
>
> The throttle support has been added in the generic code. Remove
> the driver-specific throttle support.
>
> Besides the throttle, perf_event_overflow may return true because of
> event_limit. It already does an inatomic event disable. The pmu->stop
> is not required either.
>
> Tested-by: Thomas Richter <tmricht@...ux.ibm.com>
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> Cc: Thomas Richter <tmricht@...ux.ibm.com>
> Cc: linux-s390@...r.kernel.org
> ---
> arch/s390/kernel/perf_cpum_cf.c | 2 --
> arch/s390/kernel/perf_cpum_sf.c | 5 +----
> 2 files changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/arch/s390/kernel/perf_cpum_cf.c b/arch/s390/kernel/perf_cpum_cf.c
> index e657fad7e376..6a262e198e35 100644
> --- a/arch/s390/kernel/perf_cpum_cf.c
> +++ b/arch/s390/kernel/perf_cpum_cf.c
> @@ -980,8 +980,6 @@ static int cfdiag_push_sample(struct perf_event *event,
> }
>
> overflow = perf_event_overflow(event, &data, ®s);
> - if (overflow)
> - event->pmu->stop(event, 0);
>
> perf_event_update_userpage(event);
> return overflow;
> diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c
> index ad22799d8a7d..91469401f2c9 100644
> --- a/arch/s390/kernel/perf_cpum_sf.c
> +++ b/arch/s390/kernel/perf_cpum_sf.c
> @@ -1072,10 +1072,7 @@ static int perf_push_sample(struct perf_event *event,
> overflow = 0;
> if (perf_event_exclude(event, ®s, sde_regs))
> goto out;
> - if (perf_event_overflow(event, &data, ®s)) {
> - overflow = 1;
> - event->pmu->stop(event, 0);
> - }
> + overflow = perf_event_overflow(event, &data, ®s);
> perf_event_update_userpage(event);
> out:
> return overflow;
> --
> 2.38.1
Hi all,
This seems to break POLL_HUP delivery to userspace - when event_limit reaches 0
>From perf_event_open man page:
PERF_EVENT_IOC_REFRESH
Non-inherited overflow counters can use this to enable a
counter for a number of overflows specified by the
argument, after which it is disabled. Subsequent calls of
this ioctl add the argument value to the current count. An
overflow notification with POLL_IN set will happen on each
overflow until the count reaches 0; when that happens a
notification with POLL_HUP set is sent and the event is
disabled.
When the event_limit reaches 0, the POLL_HUP signal is expected to be
sent. Prior to this patch, an explicit call to event->stop() was made,
which may have contributed to ensuring that the POLL_HUP signal was
ultimately delivered. However, after this change, I often did not
observe the POLL_HUP signal being delivered as expected in the end
Example program:
output:
Computation result: 49951804672
count.hup: 0 count.pollin: 22
Expected output should be:
count.hup: 1 in the end
#define _GNU_SOURCE
#include <time.h>
#include <stdbool.h>
#include <signal.h>
#include <poll.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <time.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#include <linux/perf_event.h>
static struct signal_counts {
int in;
int out;
int hup;
int unknown;
} count;
static unsigned long sample_type = PERF_SAMPLE_IP | PERF_SAMPLE_TID |
PERF_SAMPLE_TIME | PERF_SAMPLE_ADDR | PERF_SAMPLE_READ |
PERF_SAMPLE_ID | PERF_SAMPLE_CPU |
PERF_SAMPLE_PERIOD | PERF_SAMPLE_STREAM_ID | PERF_SAMPLE_RAW;
static void sighandler(int signum, siginfo_t *info, void *uc)
{
switch(info->si_code) {
case POLL_IN: count.in++; break;
case POLL_OUT: count.out++; break;
case POLL_HUP: count.hup++; break;
default: count.unknown++; break;
}
}
void generate_load(unsigned long long iterations) {
unsigned long long sum = 0;
srand(time(0));
for (unsigned long long i = 0; i < iterations; ++i) {
int rnd = rand();
sum += (rnd ^ (rnd >> 3)) % 1000;
}
printf("Computation result: %llu\n", sum);
}
void perf_attr(struct perf_event_attr *pe,
unsigned long config, unsigned long period, bool freq,
unsigned long bits)
{
memset(pe, 0, sizeof(struct perf_event_attr));
pe->size = sizeof(struct perf_event_attr);
pe->type = PERF_TYPE_HARDWARE;
pe->config = PERF_COUNT_HW_CPU_CYCLES;
pe->exclude_kernel = 0;
pe->sample_period = 50000;
pe->freq = 1;
pe->disabled = 1;
pe->config = config;
pe->freq = freq;
pe->sample_type = bits;
}
int main(int argc, char **argv)
{
int fd, signo = SIGIO, rc = -1;
struct sigaction sa, sa_old;
struct perf_event_attr pe;
perf_attr(&pe, PERF_COUNT_HW_CPU_CYCLES, 50000, 1, sample_type);
/* Set up overflow handler */
memset(&sa, 0, sizeof(struct sigaction));
memset(&sa_old, 0, sizeof(struct sigaction));
sa.sa_sigaction = sighandler;
sa.sa_flags = SA_SIGINFO;
if (sigaction(signo, &sa, &sa_old) < 0)
goto out;
fd = syscall(__NR_perf_event_open, &pe, 0, -1, -1, 0);
if (fd < 0)
return rc;
rc = fcntl(fd, F_SETFL, O_RDWR | O_NONBLOCK | O_ASYNC);
rc |= fcntl(fd, F_SETSIG, signo);
rc |= fcntl(fd, F_SETOWN, getpid());
if (rc)
goto out;
rc = ioctl(fd, PERF_EVENT_IOC_REFRESH, 2500);
if (rc)
goto out;
generate_load(100000000ULL);
sigaction(signo, &sa_old, NULL);
printf("count.hup: %d count.pollin: %d\n", count.hup, count.in);
close(fd);
return 0;
out:
return rc;
}
Thank you,
Sumanth
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