The new generic snapshot search gives a similar result as the reimplemented version of it here. One slight difference is in the pointer fixup. SPE has:
*head += mm->len; *old = *head - mm->len;
Which gives exactly the same result but written in reverse order to the generic one:
*old = *head; *head += mm->len;
SPE also had a special fixup cases (if (head >= buffer_size)):
* head > isn't needed because the SPE driver always wraps them, and __auxtrace_mmap__read() handles that anyway. * head == buffer_size isn't wrapped by the driver, but it just indicates 'full' which doesn't mean wrapped any more or less than any other index in the buffer.
Both of these cases are covered by the 512 byte search.
It also didn't have the special case for old > head for when the wrap heuristic fails but the pointers showed a wrap had happened.
The other feature lost is that this search only looked from head to the end of the buffer, rather than always at the last 512 bytes. This was flawed because once head is close to the end, it's likely it could contain zero padding from actual SPE data and a wrap would be missed. It's better to err on the side of caution and mark as a wrap, rather than trying to optimize by limiting the search from head onwards. This can mistake old data as evidence of a wrap, but for false positives [head..mm->len] contains zero data. This should be fine, as zero data are treated as PAD packets and discarded during decoding.
Reviewed-by: Leo Yan leo.yan@arm.com Signed-off-by: James Clark james.clark@linaro.org --- tools/perf/arch/arm64/util/arm-spe.c | 147 +---------------------------------- 1 file changed, 2 insertions(+), 145 deletions(-)
diff --git a/tools/perf/arch/arm64/util/arm-spe.c b/tools/perf/arch/arm64/util/arm-spe.c index 1ba803a8d9b4..8d6a2bde2892 100644 --- a/tools/perf/arch/arm64/util/arm-spe.c +++ b/tools/perf/arch/arm64/util/arm-spe.c @@ -26,7 +26,6 @@ #include "../../../util/record.h" #include "../../../util/header.h" #include "../../../util/arm-spe.h" -#include <tools/libc_compat.h> // reallocarray
#define ARM_SPE_CPU_MAGIC 0x1010101010101010ULL
@@ -37,8 +36,6 @@ struct arm_spe_recording { struct auxtrace_record itr; struct perf_pmu *arm_spe_pmu; struct evlist *evlist; - int wrapped_cnt; - bool *wrapped; };
/* Iterate config list to detect if the "freq" parameter is set */ @@ -497,146 +494,6 @@ static int arm_spe_snapshot_finish(struct auxtrace_record *itr) return ret; }
-static int arm_spe_alloc_wrapped_array(struct arm_spe_recording *ptr, int idx) -{ - bool *wrapped; - int cnt = ptr->wrapped_cnt, new_cnt, i; - - /* - * No need to allocate, so return early. - */ - if (idx < cnt) - return 0; - - /* - * Make ptr->wrapped as big as idx. - */ - new_cnt = idx + 1; - - /* - * Free'ed in arm_spe_recording_free(). - */ - wrapped = reallocarray(ptr->wrapped, new_cnt, sizeof(bool)); - if (!wrapped) - return -ENOMEM; - - /* - * init new allocated values. - */ - for (i = cnt; i < new_cnt; i++) - wrapped[i] = false; - - ptr->wrapped_cnt = new_cnt; - ptr->wrapped = wrapped; - - return 0; -} - -static bool arm_spe_buffer_has_wrapped(unsigned char *buffer, - size_t buffer_size, u64 head) -{ - u64 i, watermark; - u64 *buf = (u64 *)buffer; - size_t buf_size = buffer_size; - - /* - * Defensively handle the case where head might be continually increasing - if its value is - * equal or greater than the size of the ring buffer, then we can safely determine it has - * wrapped around. Otherwise, continue to detect if head might have wrapped. - */ - if (head >= buffer_size) - return true; - - /* - * We want to look the very last 512 byte (chosen arbitrarily) in the ring buffer. - */ - watermark = buf_size - 512; - - /* - * The value of head is somewhere within the size of the ring buffer. This can be that there - * hasn't been enough data to fill the ring buffer yet or the trace time was so long that - * head has numerically wrapped around. To find we need to check if we have data at the - * very end of the ring buffer. We can reliably do this because mmap'ed pages are zeroed - * out and there is a fresh mapping with every new session. - */ - - /* - * head is less than 512 byte from the end of the ring buffer. - */ - if (head > watermark) - watermark = head; - - /* - * Speed things up by using 64 bit transactions (see "u64 *buf" above) - */ - watermark /= sizeof(u64); - buf_size /= sizeof(u64); - - /* - * If we find trace data at the end of the ring buffer, head has been there and has - * numerically wrapped around at least once. - */ - for (i = watermark; i < buf_size; i++) - if (buf[i]) - return true; - - return false; -} - -static int arm_spe_find_snapshot(struct auxtrace_record *itr, int idx, - struct auxtrace_mmap *mm, unsigned char *data, - u64 *head, u64 *old) -{ - int err; - bool wrapped; - struct arm_spe_recording *ptr = - container_of(itr, struct arm_spe_recording, itr); - - /* - * Allocate memory to keep track of wrapping if this is the first - * time we deal with this *mm. - */ - if (idx >= ptr->wrapped_cnt) { - err = arm_spe_alloc_wrapped_array(ptr, idx); - if (err) - return err; - } - - /* - * Check to see if *head has wrapped around. If it hasn't only the - * amount of data between *head and *old is snapshot'ed to avoid - * bloating the perf.data file with zeros. But as soon as *head has - * wrapped around the entire size of the AUX ring buffer it taken. - */ - wrapped = ptr->wrapped[idx]; - if (!wrapped && arm_spe_buffer_has_wrapped(data, mm->len, *head)) { - wrapped = true; - ptr->wrapped[idx] = true; - } - - pr_debug3("%s: mmap index %d old head %zu new head %zu size %zu\n", - __func__, idx, (size_t)*old, (size_t)*head, mm->len); - - /* - * No wrap has occurred, we can just use *head and *old. - */ - if (!wrapped) - return 0; - - /* - * *head has wrapped around - adjust *head and *old to pickup the - * entire content of the AUX buffer. - */ - if (*head >= mm->len) { - *old = *head - mm->len; - } else { - *head += mm->len; - *old = *head - mm->len; - } - - return 0; -} - static u64 arm_spe_reference(struct auxtrace_record *itr __maybe_unused) { struct timespec ts; @@ -651,7 +508,6 @@ static void arm_spe_recording_free(struct auxtrace_record *itr) struct arm_spe_recording *sper = container_of(itr, struct arm_spe_recording, itr);
- zfree(&sper->wrapped); free(sper); }
@@ -674,7 +530,8 @@ struct auxtrace_record *arm_spe_recording_init(int *err, sper->arm_spe_pmu = arm_spe_pmu; sper->itr.snapshot_start = arm_spe_snapshot_start; sper->itr.snapshot_finish = arm_spe_snapshot_finish; - sper->itr.find_snapshot = arm_spe_find_snapshot; + sper->itr.find_snapshot = auxtrace_record__default_find_snapshot; + sper->itr.snapshot_search_bytes = 512; sper->itr.parse_snapshot_options = arm_spe_parse_snapshot_options; sper->itr.recording_options = arm_spe_recording_options; sper->itr.info_priv_size = arm_spe_info_priv_size;