Messages in this thread | | | Subject | Re: [PATCH 6/6] coresight: etm-perf: Add support for ETR backend | From | Suzuki K Poulose <> | Date | Fri, 13 Jul 2018 12:23:02 +0100 |
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On 12/07/18 21:57, Mathieu Poirier wrote: > Hi Suzuki, > > On Wed, Jul 11, 2018 at 03:16:39PM +0100, Suzuki K Poulose wrote: >> Add support for using TMC-ETR as backend for ETM perf tracing. >> We use software double buffering at the moment. i.e, the TMC-ETR >> uses a separate buffer than the perf ring buffer. The data is >> copied to the perf ring buffer once a session completes. >> >> The TMC-ETR would try to match the larger of perf ring buffer >> or the ETR buffer size configured via sysfs, scaling down to >> a minimum limit of 1MB. >> >> Cc: Mathieu Poirier <mathieu.poirier@linaro.org> >> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >> --- >> drivers/hwtracing/coresight/coresight-tmc-etr.c | 265 +++++++++++++++++++++++- >> drivers/hwtracing/coresight/coresight-tmc.h | 2 + >> 2 files changed, 265 insertions(+), 2 deletions(-)
>> +/* >> + * 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) >> +{ >> + long bytes, to_copy; >> + long pg_idx, pg_offset, src_offset; >> + unsigned long head = etr_perf->head; >> + char **dst_pages, *src_buf; >> + struct etr_buf *etr_buf = etr_perf->etr_buf; >> + >> + head = PERF_IDX2OFF(etr_perf->head, etr_perf); > > I'm puzzled here. Since etr_perf->head is set in tmc_etr_set_perf_buffer() to > the value of handle->head, its value is always within the range of the perf ring
IIUC, the handle->head is not necessarily guaranteed to be within the aux-ring buffer.
> buffer. In tmc_etr_alloc_perf_buffer() etr_perf->nr_pages is set to the number > of pages present in that ring buffer. As such I'm not sure as to why we need > the PERF_IDX2OFF() macro. > > It seems to me that "head = etr_perf->head;" above is sufficient. >
We need to do the step at some point, which could be moved to set_perf_buffer.
>> + 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; >> + >> + while (to_copy > 0) { >> + /* >> + * We can copy minimum of : > > s/We can copy minimum of :/In one iteration we can copy a minimum of:/ > > If I'm wrong about the PERF_IDX2OFF(), don't bother respinning just for that.
I have some more fixes for handling the different modes (sysfs vs perf), which I can include in the v2.
Suzuki
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