Messages in this thread | | | From | Mathieu Poirier <> | Date | Mon, 16 Jul 2018 09:05:43 -0600 | Subject | Re: [PATCH 6/6] coresight: etm-perf: Add support for ETR backend |
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On Fri, 13 Jul 2018 at 05:23, Suzuki K Poulose <Suzuki.Poulose@arm.com> wrote: > > 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.
I just looked at the ETB code and you are correct.
> > > 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.
That's a good idea.
> > >> + 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.
Very well.
> > Suzuki
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