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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,88 @@ | ||
| From 71540e46aef1da5595b817563ee231c6a3aae3df Mon Sep 17 00:00:00 2001 | ||
| From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | ||
| Date: Sat, 14 Oct 2023 09:36:58 -0400 | ||
| Subject: [PATCH] consumer: Fix discarded events aggregation | ||
|
|
||
| - Print error message if overflow is detected on 64-bit, | ||
| - Do not update the channel counter if overflow is detected on 64-bit, | ||
| so the situation can be recovered on the next aggregation if it was | ||
| caused by a spurious race condition, | ||
| - Change (1ULL << (CAA_BITS_PER_LONG - 1)) for (1ULL << 32), thus fixing | ||
| an off-by-one in the shift on 32-bit. | ||
| - Use an explicit shift of 32 rather than CAA_BITS_PER_LONG to eliminate | ||
| too-large shift warnings on 64-bit. | ||
|
|
||
| Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | ||
| Change-Id: I1a0fca2dcf6e3fe5ec37509838515545b5ee9062 | ||
| --- | ||
|
|
||
| diff --git a/src/common/consumer/consumer-stream.cpp b/src/common/consumer/consumer-stream.cpp | ||
| index 0742c86..2801f1d 100644 | ||
| --- a/src/common/consumer/consumer-stream.cpp | ||
| +++ b/src/common/consumer/consumer-stream.cpp | ||
| @@ -77,13 +77,42 @@ | ||
| consumer_stream_data_assert_locked_all(stream); | ||
| } | ||
|
|
||
| +static void aggregate_discarded_events(uint64_t *_chan_discarded_events, | ||
| + uint64_t *_stream_last_discarded_events, | ||
| + uint64_t stream_discarded_events) | ||
| +{ | ||
| + uint64_t stream_last_discarded_events = *_stream_last_discarded_events; | ||
| + uint64_t stream_delta = 0; | ||
| + | ||
| + if (stream_discarded_events < stream_last_discarded_events) { | ||
| + if (CAA_BITS_PER_LONG >= 64) { | ||
| + ERR("Unexpected events discarded counter 64-bit overflow: prev = %" PRIu64 " current = %" PRIu64, | ||
| + stream_last_discarded_events, stream_discarded_events); | ||
| + /* | ||
| + * Unexpected counter overflow: don't update the counter, | ||
| + * so if this is caused by a race condition, we can | ||
| + * recover on the next aggregation. | ||
| + */ | ||
| + return; | ||
| + } else { | ||
| + /* | ||
| + * A 32-bit overflow is detected. We assume only one | ||
| + * wrap-around has occurred. | ||
| + */ | ||
| + stream_delta += 1ULL << 32; | ||
| + } | ||
| + } | ||
| + stream_delta += stream_discarded_events - stream_last_discarded_events; | ||
| + *_chan_discarded_events += stream_delta; | ||
| + *_stream_last_discarded_events = stream_discarded_events; | ||
| +} | ||
| + | ||
| /* Only used for data streams. */ | ||
| static int consumer_stream_update_stats(struct lttng_consumer_stream *stream, | ||
| const struct stream_subbuffer *subbuf) | ||
| { | ||
| int ret = 0; | ||
| uint64_t sequence_number; | ||
| - const uint64_t discarded_events = subbuf->info.data.events_discarded; | ||
|
|
||
| if (!subbuf->info.data.sequence_number.is_set) { | ||
| /* Command not supported by the tracer. */ | ||
| @@ -111,18 +140,9 @@ | ||
| goto end; | ||
| } | ||
| stream->last_sequence_number = sequence_number; | ||
| - | ||
| - if (discarded_events < stream->last_discarded_events) { | ||
| - /* | ||
| - * Overflow has occurred. We assume only one wrap-around | ||
| - * has occurred. | ||
| - */ | ||
| - stream->chan->discarded_events += (1ULL << (CAA_BITS_PER_LONG - 1)) - | ||
| - stream->last_discarded_events + discarded_events; | ||
| - } else { | ||
| - stream->chan->discarded_events += discarded_events - stream->last_discarded_events; | ||
| - } | ||
| - stream->last_discarded_events = discarded_events; | ||
| + aggregate_discarded_events(&stream->chan->discarded_events, | ||
| + &stream->last_discarded_events, | ||
| + subbuf->info.data.events_discarded); | ||
| ret = 0; | ||
|
|
||
| end: |
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