[PATCH V2 4/6] tools/perf: Allocate and setup aux buffer queue to help co-relate with other events across CPU's

[Athira Rajeev]

> On 15 Sep 2025, at 8:38 PM, Adrian Hunter <adrian.hunter at intel.com> wrote:
> 
> On 15/09/2025 10:27, Athira Rajeev wrote:
>> When the Dispatch Trace Log data is collected along with other events
>> like sched tracepoint events, it needs to be correlated and present
>> interleaved along with these events. Perf events can be collected
>> parallely across the CPUs. Hence it needs to be ensured events/dtl
>> entries are processed in timestamp order.
>> 
>> An auxtrace_queue is created for each CPU. Data within each queue is in
>> increasing order of timestamp. Each auxtrace queue has a array/list of
>> auxtrace buffers. When processing the auxtrace buffer, the data is
>> mmapp'ed. All auxtrace queues is maintained in auxtrace heap. Each queue
>> has a queue number and a timestamp. The queues are sorted/added to head
>> based on the time stamp. So always the lowest timestamp (entries to be
>> processed first) is on top of the heap.
>> 
>> The auxtrace queue needs to be allocated and heap needs to be populated
>> in the sorted order of timestamp. The queue needs to be filled with data
>> only once via powerpc_vpadtl__update_queues() function.
>> powerpc_vpadtl__setup_queues() iterates through all the entries to
>> allocate and setup the auxtrace queue. To add to auxtrace heap, it is
>> required to fetch the timebase of first entry for each of the queue.
>> 
>> The first entry in the queue for VPA DTL PMU has the boot timebase,
>> frequency details which are needed to get timestamp which is required to
>> correlate with other events. The very next entry is the actual trace data
>> that provides timestamp for occurrence of DTL event. Formula used to get
>> the timestamp from dtl entry is:
>> 
>> ((timbase from DTL entry - boot time) / frequency) * 1000000000
>> 
>> powerpc_vpadtl_decode() adds the boot time and frequency as part of
>> powerpc_vpadtl_queue structure so that it can be reused. Each of the
>> dtl_entry is of 48 bytes size. Sometimes it could happen that one buffer
>> is only partially processed (if the timestamp of occurrence of another
>> event is more than currently processed element in queue, it will move on
>> to next event). In order to keep track of position of buffer, additional
>> fields is added to powerpc_vpadtl_queue structure.
>> 
>> Signed-off-by: Athira Rajeev <atrajeev at linux.ibm.com>
>> ---
>> Changelog:
>> Addressed review comments from Adrian
>> - Moved time calculation to separate function
>> 
>> tools/perf/util/powerpc-vpadtl.c | 226 ++++++++++++++++++++++++++++++-
>> 1 file changed, 223 insertions(+), 3 deletions(-)
>> 
>> diff --git a/tools/perf/util/powerpc-vpadtl.c b/tools/perf/util/powerpc-vpadtl.c
>> index 9098cbe00bfd..637abde60f44 100644
>> --- a/tools/perf/util/powerpc-vpadtl.c
>> +++ b/tools/perf/util/powerpc-vpadtl.c
>> @@ -10,6 +10,8 @@
>> #include "session.h"
>> #include "debug.h"
>> #include "powerpc-vpadtl.h"
>> +#include "sample.h"
>> +#include "tool.h"
>> 
>> /*
>>  * Structure to save the auxtrace queue
>> @@ -38,6 +40,14 @@ struct powerpc_vpadtl_queue {
>> struct auxtrace_buffer *buffer;
>> struct thread *thread;
>> bool on_heap;
>> + struct powerpc_vpadtl_entry *dtl;
>> + u64 timestamp;
>> + unsigned long pkt_len;
>> + unsigned long buf_len;
>> + u64 boot_tb;
>> + u64 tb_freq;
>> + unsigned int tb_buffer;
>> + unsigned int size;
>> bool done;
>> pid_t pid;
>> pid_t tid;
>> @@ -112,6 +122,33 @@ static void powerpc_vpadtl_dump(struct powerpc_vpadtl *vpa __maybe_unused,
>> }
>> }
>> 
>> +static unsigned long long powerpc_vpadtl_timestamp(struct powerpc_vpadtl_queue *vpaq)
>> +{
>> + struct powerpc_vpadtl_entry *record = vpaq->dtl;
>> + double result, div;
>> + double boot_freq;
>> + unsigned long long boot_tb;
>> + unsigned long long diff;
>> + unsigned long long timestamp = 0;
> 
> Prettier in descending line length e.g.
> 
> struct powerpc_vpadtl_entry *record = vpaq->dtl;
> unsigned long long timestamp = 0;
> unsigned long long boot_tb;
> unsigned long long diff;
> double result, div;
> double boot_freq;
> 
>> +
>> + /*
>> +  * Formula used to get timestamp that can be co-related with
>> +  * other perf events:
>> +  * ((timbase from DTL entry - boot time) / frequency) * 1000000000
>> +  */
>> + if (record->timebase) {
>> + boot_tb = vpaq->boot_tb;
>> + boot_freq = vpaq->tb_freq;
>> + diff = be64_to_cpu(record->timebase) - boot_tb;
>> + div = diff / boot_freq;
>> + result = div;
>> + result = result * 1000000000;
>> + timestamp = result;
>> + }
>> +
>> + return timestamp;
>> +}
>> +
>> static struct powerpc_vpadtl *session_to_vpa(struct perf_session *session)
>> {
>> return container_of(session->auxtrace, struct powerpc_vpadtl, auxtrace);
>> @@ -124,12 +161,195 @@ static void powerpc_vpadtl_dump_event(struct powerpc_vpadtl *vpa, unsigned char
>> powerpc_vpadtl_dump(vpa, buf, len);
>> }
>> 
>> +static int powerpc_vpadtl_get_buffer(struct powerpc_vpadtl_queue *vpaq)
>> +{
>> + struct auxtrace_buffer *buffer = vpaq->buffer;
>> + struct auxtrace_queues *queues = &vpaq->vpa->queues;
>> + struct auxtrace_queue *queue;
>> +
>> + queue = &queues->queue_array[vpaq->queue_nr];
>> + buffer = auxtrace_buffer__next(queue, buffer);
>> +
>> + if (!buffer)
>> + return 0;
>> +
>> + vpaq->buffer = buffer;
>> + vpaq->size = buffer->size;
>> +
>> + /* If the aux_buffer doesn't have data associated, try to load it */
>> + if (!buffer->data) {
>> + /* get the file desc associated with the perf data file */
>> + int fd = perf_data__fd(vpaq->vpa->session->data);
>> +
>> + buffer->data = auxtrace_buffer__get_data(buffer, fd);
>> + if (!buffer->data)
>> + return -ENOMEM;
>> + }
>> +
>> + vpaq->buf_len = buffer->size;
>> +
>> + if (buffer->size % dtl_entry_size)
>> + vpaq->buf_len = buffer->size - (buffer->size % dtl_entry_size);
>> +
>> + if (vpaq->tb_buffer != buffer->buffer_nr) {
>> + vpaq->pkt_len = 0;
>> + vpaq->tb_buffer = 0;
>> + }
>> +
>> + return 1;
>> +}
>> +
>> +/*
>> + * The first entry in the queue for VPA DTL PMU has the boot timebase,
>> + * frequency details which are needed to get timestamp which is required to
>> + * correlate with other events. Save the boot_tb and tb_freq as part of
>> + * powerpc_vpadtl_queue. The very next entry is the actual trace data to
>> + * be returned.
>> + */
>> +static int powerpc_vpadtl_decode(struct powerpc_vpadtl_queue *vpaq)
>> +{
>> + int ret;
>> + char *buf;
>> + struct boottb_freq *boottb;
>> +
>> + ret = powerpc_vpadtl_get_buffer(vpaq);
>> + if (ret <= 0)
>> + return ret;
>> +
>> + boottb = (struct boottb_freq *)vpaq->buffer->data;
>> + if (boottb->timebase == 0) {
>> + vpaq->boot_tb = boottb->boot_tb;
>> + vpaq->tb_freq = boottb->tb_freq;
>> + vpaq->pkt_len += dtl_entry_size;
>> + }
>> +
>> + buf = vpaq->buffer->data;
>> + buf += vpaq->pkt_len;
>> + vpaq->dtl = (struct powerpc_vpadtl_entry *)buf;
>> +
>> + vpaq->tb_buffer = vpaq->buffer->buffer_nr;
>> + vpaq->buffer = NULL;
>> + vpaq->buf_len = 0;
>> +
>> + return 1;
>> +}
>> +
>> +static struct powerpc_vpadtl_queue *powerpc_vpadtl__alloc_queue(struct powerpc_vpadtl *vpa,
>> + unsigned int queue_nr)
>> +{
>> + struct powerpc_vpadtl_queue *vpaq;
>> +
>> + vpaq = zalloc(sizeof(*vpaq));
>> + if (!vpaq)
>> + return NULL;
>> +
>> + vpaq->vpa = vpa;
>> + vpaq->queue_nr = queue_nr;
>> +
>> + return vpaq;
>> +}
>> +
>> +/*
>> + * When the Dispatch Trace Log data is collected along with other events
>> + * like sched tracepoint events, it needs to be correlated and present
>> + * interleaved along with these events. Perf events can be collected
>> + * parallely across the CPUs.
>> + *
>> + * An auxtrace_queue is created for each CPU. Data within each queue is in
>> + * increasing order of timestamp. Allocate and setup auxtrace queues here.
>> + * All auxtrace queues is maintained in auxtrace heap in the increasing order
>> + * of timestamp. So always the lowest timestamp (entries to be processed first)
>> + * is on top of the heap.
>> + *
>> + * To add to auxtrace heap, fetch the timestamp from first DTL entry
>> + * for each of the queue.
>> + */
>> +static int powerpc_vpadtl__setup_queue(struct powerpc_vpadtl *vpa,
>> + struct auxtrace_queue *queue,
>> + unsigned int queue_nr)
>> +{
>> + struct powerpc_vpadtl_queue *vpaq = queue->priv;
>> +
>> + if (list_empty(&queue->head) || vpaq)
>> + return 0;
>> +
>> + vpaq = powerpc_vpadtl__alloc_queue(vpa, queue_nr);
>> + if (!vpaq)
>> + return -ENOMEM;
>> +
>> + queue->priv = vpaq;
>> +
>> + if (queue->cpu != -1)
>> + vpaq->cpu = queue->cpu;
>> +
>> + if (!vpaq->on_heap) {
>> + int ret;
>> +retry:
>> + ret = powerpc_vpadtl_decode(vpaq);
>> + if (!ret)
>> + return 0;
>> +
>> + if (ret < 0)
>> + goto retry;
>> +
>> + vpaq->timestamp = powerpc_vpadtl_timestamp(vpaq);
>> +
>> + ret = auxtrace_heap__add(&vpa->heap, queue_nr, vpaq->timestamp);
>> + if (ret)
>> + return ret;
>> + vpaq->on_heap = true;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static int powerpc_vpadtl__setup_queues(struct powerpc_vpadtl *vpa)
>> +{
>> + unsigned int i;
>> + int ret;
>> +
>> + for (i = 0; i < vpa->queues.nr_queues; i++) {
>> + ret = powerpc_vpadtl__setup_queue(vpa, &vpa->queues.queue_array[i], i);
>> + if (ret)
>> + return ret;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static int powerpc_vpadtl__update_queues(struct powerpc_vpadtl *vpa)
>> +{
>> + if (vpa->queues.new_data) {
>> + vpa->queues.new_data = false;
>> + return powerpc_vpadtl__setup_queues(vpa);
>> + }
>> +
>> + return 0;
>> +}
>> +
>> static int powerpc_vpadtl_process_event(struct perf_session *session __maybe_unused,
> 
> session is not __maybe_unused
> 
Sure

I will address these changes in V3

Thanks
Athira
>>  union perf_event *event __maybe_unused,
>> -  struct perf_sample *sample __maybe_unused,
>> -  const struct perf_tool *tool __maybe_unused)
>> +  struct perf_sample *sample,
>> +  const struct perf_tool *tool)
>> {
>> - return 0;
>> + struct powerpc_vpadtl *vpa = session_to_vpa(session);
>> + int err = 0;
>> +
>> + if (dump_trace)
>> + return 0;
>> +
>> + if (!tool->ordered_events) {
>> + pr_err("VPA requires ordered events\n");
>> + return -EINVAL;
>> + }
>> +
>> + if (sample->time) {
>> + err = powerpc_vpadtl__update_queues(vpa);
>> + if (err)
>> + return err;
>> + }
>> +
>> + return err;
>> }
>> 
>> /*