Messages in this thread | | | Subject | Re: [PATCH v2 14/17] coresight: trbe: Make sure we have enough space | From | Anshuman Khandual <> | Date | Fri, 1 Oct 2021 10:10:26 +0530 |
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On 9/22/21 3:46 PM, Suzuki K Poulose wrote: > 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.
Okay.
> >> >>> 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.
Got it.
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