On 2/3/23 1:42 PM, Andrii Nakryiko wrote:
On Fri, Feb 3, 2023 at 10:31 AM Yonghong Song <yhs@xxxxxxxx> wrote:
On 2/1/23 10:25 PM, Jon Doron wrote:
From: Jon Doron <jond@xxxxxx>
Add option to set when the perf buffer should wake up, by default the
perf buffer becomes signaled for every event that is being pushed to it.
In case of a high throughput of events it will be more efficient to wake
up only once you have X events ready to be read.
So your application can wakeup once and drain the entire perf buffer.
Signed-off-by: Jon Doron <jond@xxxxxx>
---
tools/lib/bpf/libbpf.c | 4 ++--
tools/lib/bpf/libbpf.h | 3 ++-
2 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index eed5cec6f510..6b30ff13922b 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -11719,8 +11719,8 @@ struct perf_buffer *perf_buffer__new(int map_fd, size_t page_cnt,
attr.config = PERF_COUNT_SW_BPF_OUTPUT;
attr.type = PERF_TYPE_SOFTWARE;
attr.sample_type = PERF_SAMPLE_RAW;
- attr.sample_period = 1;
- attr.wakeup_events = 1;
+ attr.sample_period = OPTS_GET(opts, wakeup_events, 1);
+ attr.wakeup_events = OPTS_GET(opts, wakeup_events, 1);
p.attr = &attr;
p.sample_cb = sample_cb;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 8777ff21ea1d..e83c0a915dc7 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -1246,8 +1246,9 @@ typedef void (*perf_buffer_lost_fn)(void *ctx, int cpu, __u64 cnt);
/* common use perf buffer options */
struct perf_buffer_opts {
size_t sz;
+ __u32 wakeup_events;
Since you are adding wakeup_events here, do you think it make sense
to add sample_period to struct perf_buffer_opts as well? In some cases,
users might want to have different values for sample_period and
wakeup_events, e.g., smaller sample_period to accumulate data and
larger wakeup_events to wakeup user space poll?
It's not clear to me from reading perf_event_open manpage what
"sample_period" means for perf buffer. What will happen when we have
sample_period != wakeup_events?
The following is my understanding. Let us sample_period = 10,
wakeup_events = 100.
Every 10 samples, kernel overflow handler is called and the the sample
data are written into ring buffer.
Every 100 samples, the poll() syscall is waken up to give userspace
a chance to read the data.
In this particular case, it is possible that user space may miss
some samples at the end if no special handling (I forgot what it is).
But if the user space doesn't really care, it might be okay with
such a configuration.
It would be great if some perf expert can clarify whether my
understanding is correct or not.
};
-#define perf_buffer_opts__last_field sz
+#define perf_buffer_opts__last_field wakeup_events
/**
* @brief **perf_buffer__new()** creates BPF perfbuf manager for a specified
