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SubjectRe: [PATCH v2] coresight: tmc-etr: Fix updating buffer in not-snapshot mode.
On Mon, 12 Aug 2019 at 16:11, Yabin Cui <yabinc@google.com> wrote:
>
> TMC etr always copies all available data to perf aux buffer, which
> may exceed the available space in perf aux buffer. It isn't suitable
> for not-snapshot mode, because:
> 1) It may overwrite previously written data.
> 2) It may make the perf_event_mmap_page->aux_head report having more
> or less data than the reality.
>
> So change to only copy the latest data fitting the available space in
> perf aux buffer.
>
> Signed-off-by: Yabin Cui <yabinc@google.com>
> ---
>
> v1 -> v2: copy the latest data instead of the earliest data.
>
> ---
> .../hwtracing/coresight/coresight-tmc-etr.c | 18 +++++++++++-------
> 1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> index 17006705287a..676dcb4cf0e2 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> @@ -1410,9 +1410,10 @@ static void tmc_free_etr_buffer(void *config)
> * tmc_etr_sync_perf_buffer: Copy the actual trace data from the hardware
> * buffer to the perf ring buffer.
> */
> -static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf)
> +static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf,
> + unsigned long to_copy)
> {
> - long bytes, to_copy;
> + long bytes;
> long pg_idx, pg_offset, src_offset;
> unsigned long head = etr_perf->head;
> char **dst_pages, *src_buf;
> @@ -1422,8 +1423,7 @@ static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf)
> pg_idx = head >> PAGE_SHIFT;
> pg_offset = head & (PAGE_SIZE - 1);
> dst_pages = (char **)etr_perf->pages;
> - src_offset = etr_buf->offset;
> - to_copy = etr_buf->len;
> + src_offset = etr_buf->offset + etr_buf->len - to_copy;
>
> while (to_copy > 0) {
> /*
> @@ -1434,6 +1434,8 @@ static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf)
> * 3) what is available in the destination page.
> * in one iteration.
> */
> + if (src_offset >= etr_buf->size)
> + src_offset -= etr_buf->size;
> bytes = tmc_etr_buf_get_data(etr_buf, src_offset, to_copy,
> &src_buf);
> if (WARN_ON_ONCE(bytes <= 0))
> @@ -1454,8 +1456,6 @@ static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf)
>
> /* Move source pointers */
> src_offset += bytes;
> - if (src_offset >= etr_buf->size)
> - src_offset -= etr_buf->size;
> }
> }

Yes, much better now. I have applied your work.

Thanks,
Mathieu

>
> @@ -1501,7 +1501,11 @@ tmc_update_etr_buffer(struct coresight_device *csdev,
> spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
> size = etr_buf->len;
> - tmc_etr_sync_perf_buffer(etr_perf);
> + if (!etr_perf->snapshot && size > handle->size) {
> + size = handle->size;
> + lost = true;
> + }
> + tmc_etr_sync_perf_buffer(etr_perf, size);
>
> /*
> * In snapshot mode we simply increment the head by the number of byte
> --
> 2.23.0.rc1.153.gdeed80330f-goog
>

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