On 02/02/2023, Andrii Nakryiko wrote:
On Wed, Feb 1, 2023 at 10:26 PM Jon Doron <arilou@xxxxxxxxx> 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);
I suspect the case of
LIBBPF_OPTS(perf_buffer_opts, opts);
perf_buffer__new(...., &opts);
is not handled correctly and you end up with sample_period == wakeup_events == 0
Can you please add BPF selftests that's setting wakeup_events to zero
and separately to >1?
Hi Andrii,
I'm not sure what we are testing, when you have sample_period ==
wakeup_events == 0, it basically means to never wakeup, so let's say you
would wait on the poll_fd infinitely it will never wake you up.
When you have let's say wakeup_event != 0, you will wakeup after the
ring buffer in the perf buffer has more events than wakeup_events.
I do see your point that if someone is using the macro to build the opts
they will end with something unexpected, would you like me to treat 0 as
1 in that case?
-- Jon.
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;
};
-#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
--
2.39.1
