Messages in this thread | | | Subject | Re: [PATCH v2 14/17] coresight: trbe: Make sure we have enough space | From | Suzuki K Poulose <> | Date | Wed, 22 Sep 2021 11:16:48 +0100 |
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On 22/09/2021 10:58, Anshuman Khandual wrote: > > > On 9/21/21 7:11 PM, Suzuki K Poulose wrote: >> The TRBE driver makes sure that there is enough space for a meaningful >> run, otherwise pads the given space and restarts the offset calculation >> once. But there is no guarantee that we may find space or hit "no space". > > So what happens currently when it neither finds the required minimum buffer > space for a meaningful run nor does it hit the "no space" scenario ?
It tries once today and assumes that it will either hit :
- No space OR - Enough space
which is reasonable, given the minimum space needed is a few bytes. But this may no longer be true with other erratum workaround.
> >> Make sure that we repeat the step until, either : >> - We have the minimum space >> OR >> - There is NO space at all. >> >> Cc: Anshuman Khandual <anshuman.khandual@arm.com> >> Cc: Mathieu Poirier <mathieu.poirier@linaro.org> >> Cc: Mike Leach <mike.leach@linaro.org> >> Cc: Leo Yan <leo.yan@linaro.org> >> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> >> --- >> drivers/hwtracing/coresight/coresight-trbe.c | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c >> index 3373f4e2183b..02f9e00e2091 100644 >> --- a/drivers/hwtracing/coresight/coresight-trbe.c >> +++ b/drivers/hwtracing/coresight/coresight-trbe.c >> @@ -451,10 +451,14 @@ static unsigned long trbe_normal_offset(struct perf_output_handle *handle) >> * If the head is too close to the limit and we don't >> * have space for a meaningful run, we rather pad it >> * and start fresh. >> + * >> + * We might have to do this more than once to make sure >> + * we have enough required space. > > OR no space at all, as explained in the commit message. > Hence this comment needs an update. > >> */ >> - if (limit && ((limit - head) < trbe_min_trace_buf_size(handle))) { >> + while (limit && ((limit - head) < trbe_min_trace_buf_size(handle))) { >> trbe_pad_buf(handle, limit - head); >> limit = __trbe_normal_offset(handle); >> + head = PERF_IDX2OFF(handle->head, buf); > > Should the loop be bound with a retry limit as well ?
No. We will eventually hit No-space as we keep on padding the buffer.
Suzuki
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