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SubjectRe: [PATCH v12 12/17] tools/counter: Create Counter tools
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On 7/11/21 6:28 AM, William Breathitt Gray wrote:
> On Sat, Jul 10, 2021 at 11:53:35AM -0500, David Lechner wrote:
>> On 7/5/21 3:19 AM, William Breathitt Gray wrote:

>>> + {
>>> + /* Component data: Count 0 count */
>>> + .component.type = COUNTER_COMPONENT_COUNT,
>>> + .component.scope = COUNTER_SCOPE_COUNT,
>>> + .component.parent = 0,
>>> + /* Event type: Index */
>>> + .event = COUNTER_EVENT_INDEX,
>>> + /* Device event channel 0 */
>>> + .channel = 0,
>>> + },
>>> + {
>>> + /* Component data: Count 1 count */
>>> + .component.type = COUNTER_COMPONENT_COUNT,
>>> + .component.scope = COUNTER_SCOPE_COUNT,
>>> + .component.parent = 1,
>>> + /* Event type: Index */
>>> + .event = COUNTER_EVENT_INDEX,
>>> + /* Device event channel 0 */
>>> + .channel = 0,
>>> + },
>>> +};
>>> +
>>> +int main(void)
>>> +{
>>> + int fd;
>>> + int ret;
>>> + struct counter_event event_data[2];
>>> +
>>> + fd = open("/dev/counter0", O_RDWR);
>>> + if (fd == -1) {
>>> + perror("Unable to open /dev/counter0");
>>> + return -errno;
>>
>> errno is no longer valid after calling perror(). Since this
>> is example code, we can just return 1 instead (exit codes
>> positive number between 0 and 255 so -1 would be 255).
>
> Ack.
>
>>> + }
>>> +
>>> + ret = ioctl(fd, COUNTER_ADD_WATCH_IOCTL, watches);
>>> + if (ret == -1) {
>>> + perror("Error adding watches[0]");
>>> + return -errno;
>>> + }
>>> + ret = ioctl(fd, COUNTER_ADD_WATCH_IOCTL, watches + 1);
>>> + if (ret == -1) {
>>> + perror("Error adding watches[1]");
>>> + return -errno;
>>> + }
>>> + ret = ioctl(fd, COUNTER_ENABLE_EVENTS_IOCTL);
>>> + if (ret == -1) {
>>> + perror("Error enabling events");
>>> + return -errno;
>>> + }
>>> +
>>> + for (;;) {
>>> + ret = read(fd, event_data, sizeof(event_data));
>>> + if (ret == -1) {
>>> + perror("Failed to read event data");
>>> + return -errno;
>>> + }
>>> +
>>> + if (ret != sizeof(event_data)) {
>>> + fprintf(stderr, "Failed to read event data\n");
>>> + return -EIO;
>>> + }
>>> +
>>> + printf("Timestamp 0: %llu\tCount 0: %llu\n"
>>> + "Error Message 0: %s\n"
>>> + "Timestamp 1: %llu\tCount 1: %llu\n"
>>> + "Error Message 1: %s\n",
>>> + (unsigned long long)event_data[0].timestamp,
>>> + (unsigned long long)event_data[0].value,
>>> + strerror(event_data[0].status),
>>> + (unsigned long long)event_data[1].timestamp,
>>> + (unsigned long long)event_data[1].value,
>>> + strerror(event_data[1].status));
>>> + }
>>
>> Aren't the Count 0 and Count 1 events independent? Why should we expect to
>> always get both events at the same time in the same order?
>
> Watch 0 and Watch 1 are both triggered by the same event: a
> COUNTER_EVENT_INDEX event on device event channel 0. If we had set
> channel to 1 for Watch 1, then we would have two independent events, but
> in this case both Watches have their respective channel set to 0.

The thing that jumped out to me is that they have different parents.
But I guess I forgot that the event itself always has a scope of
device and that the component just says what value to record and
is otherwise independent of the event.

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