[PATCH V4 07/16] s390/perf: Remove driver-specific throttle support

[PATCH V4 07/16] s390/perf: Remove driver-specific throttle support

[kan.liang]

From: Kan Liang <kan.liang@linux.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@linux.ibm.com>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: linux-s390@vger.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, &regs);
-	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, &regs, sde_regs))
 		goto out;
-	if (perf_event_overflow(event, &data, &regs)) {
-		overflow = 1;
-		event->pmu->stop(event, 0);
-	}
+	overflow = perf_event_overflow(event, &data, &regs);
 	perf_event_update_userpage(event);
 out:
 	return overflow;
-- 
2.38.1

Re: [PATCH V4 07/16] s390/perf: Remove driver-specific throttle support

[Sumanth Korikkar]

On Tue, May 20, 2025 at 11:16:35AM -0700, kan.liang@linux.intel.com wrote:
> From: Kan Liang <kan.liang@linux.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@linux.ibm.com>
> Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
> Cc: Thomas Richter <tmricht@linux.ibm.com>
> Cc: linux-s390@vger.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, &regs);
> -	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, &regs, sde_regs))
>  		goto out;
> -	if (perf_event_overflow(event, &data, &regs)) {
> -		overflow = 1;
> -		event->pmu->stop(event, 0);
> -	}
> +	overflow = perf_event_overflow(event, &data, &regs);
>  	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

Re: [PATCH V4 07/16] s390/perf: Remove driver-specific throttle support

[Sumanth Korikkar]

On Wed, Jul 23, 2025 at 10:06:26AM +0200, Sumanth Korikkar wrote:
> On Tue, May 20, 2025 at 11:16:35AM -0700, kan.liang@linux.intel.com wrote:
> > From: Kan Liang <kan.liang@linux.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@linux.ibm.com>
> > Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
> > Cc: Thomas Richter <tmricht@linux.ibm.com>
> > Cc: linux-s390@vger.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, &regs);
> > -	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, &regs, sde_regs))
> >  		goto out;
> > -	if (perf_event_overflow(event, &data, &regs)) {
> > -		overflow = 1;
> > -		event->pmu->stop(event, 0);
> > -	}
> > +	overflow = perf_event_overflow(event, &data, &regs);
> >  	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;
> }

Hi Kan,

It would be great if you could share your feedback on this issue.

Thank you.

Re: [PATCH V4 07/16] s390/perf: Remove driver-specific throttle support

[Liang, Kan]

Hi Sumanth,

Sorry for the late response. I just came back from Sabbatical yesterday.

On 2025-08-06 1:37 a.m., Sumanth Korikkar wrote:
> On Wed, Jul 23, 2025 at 10:06:26AM +0200, Sumanth Korikkar wrote:
>> On Tue, May 20, 2025 at 11:16:35AM -0700, kan.liang@linux.intel.com wrote:
>>> From: Kan Liang <kan.liang@linux.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@linux.ibm.com>
>>> Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
>>> Cc: Thomas Richter <tmricht@linux.ibm.com>
>>> Cc: linux-s390@vger.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, &regs);
>>> -	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, &regs, sde_regs))
>>>  		goto out;
>>> -	if (perf_event_overflow(event, &data, &regs)) {
>>> -		overflow = 1;
>>> -		event->pmu->stop(event, 0);
>>> -	}
>>> +	overflow = perf_event_overflow(event, &data, &regs);
>>>  	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

The event_limit case also returns 1. I missed it when fixing the
throttle issue. :(

I didn't use the IOC_REFRESH before. According to the kernel code, it
reschedules all the events of the event->pmu, when the ioctl is invoked.
So we just need to move the event->pmu->stop() to the generic code as
below. It should keep the behavior unchanged.

Could you please try the below fix?

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 14ae43694833..f492cbcd3bb6 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10341,6 +10341,7 @@ static int __perf_event_overflow(struct
perf_event *event,
 		ret = 1;
 		event->pending_kill = POLL_HUP;
 		perf_event_disable_inatomic(event);
+		event->pmu->stop(event, 0);
 	}

 	if (event->attr.sigtrap) {

Thanks,
Kan

>>
>> 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;
>> }
> 
> Hi Kan,
> 
> It would be great if you could share your feedback on this issue.
> 
> Thank you.

Re: [PATCH V4 07/16] s390/perf: Remove driver-specific throttle support

[Sumanth Korikkar]

> >> 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
> 
> The event_limit case also returns 1. I missed it when fixing the
> throttle issue. :(
> 
> I didn't use the IOC_REFRESH before. According to the kernel code, it
> reschedules all the events of the event->pmu, when the ioctl is invoked.
> So we just need to move the event->pmu->stop() to the generic code as
> below. It should keep the behavior unchanged.
> 
> Could you please try the below fix?
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 14ae43694833..f492cbcd3bb6 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -10341,6 +10341,7 @@ static int __perf_event_overflow(struct
> perf_event *event,
>  		ret = 1;
>  		event->pending_kill = POLL_HUP;
>  		perf_event_disable_inatomic(event);
> +		event->pmu->stop(event, 0);
>  	}
> 
>  	if (event->attr.sigtrap) {
> 
> Thanks,
> Kan

Hi Kan,

The above fix works.

Tested-by: Sumanth Korikkar <sumanthk@linux.ibm.com>

Thank you