Commit 76cde988 authored by Suzuki K Poulose's avatar Suzuki K Poulose Committed by Ma Wupeng
Browse files

coresight: trbe: Do not truncate buffer on IRQ 

mainline inclusion
from mainline-v5.15-rc3
commit 0a5f3556
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5YCYK
CVE: NA

Reference: https://lore.kernel.org/r/20210923143919.2944311-4-suzuki.poulose@arm.com



--------------------------------------------------------------------------

The TRBE driver marks the AUX buffer as TRUNCATED when we get an IRQ
on FILL event. This has rather unwanted side-effect of the event
being disabled when there may be more space in the ring buffer.

So, instead of TRUNCATE we need a different flag to indicate
that the trace may have lost a few bytes (i.e from the point of
generating the FILL event until the IRQ is consumed). Anyways, the
userspace must use the size from RECORD_AUX headers to restrict
the "trace" decoding.

Using PARTIAL flag causes the perf tool to generate the
following warning:

  Warning:
  AUX data had gaps in it XX times out of YY!

  Are you running a KVM guest in the background?

which is pointlessly scary for a user. The other remaining options
are :
  - COLLISION - Use by SPE to indicate samples collided
  - Add a new flag - Specifically for CoreSight, doesn't sound
    so good, if we can re-use something.

Given that we don't already use the "COLLISION" flag, the above
behavior can be notified using this flag for CoreSight.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: James Clark <james.clark@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Leo Yan <leo.yan@linaro.org>
Signed-off-by: default avatarSuzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20210923143919.2944311-4-suzuki.poulose@arm.com


Signed-off-by: default avatarMathieu Poirier <mathieu.poirier@linaro.org>
parent 4ae078cc

drivers/hwtracing/coresight/coresight-trbe.c

+21 −6
Original line number Original line Diff line number Diff line
@@ -120,6 +120,25 @@ static void trbe_reset_local(void) 
	write_sysreg_s(0, SYS_TRBSR_EL1);

	write_sysreg_s(0, SYS_TRBSR_EL1);

}

}





static void trbe_report_wrap_event(struct perf_output_handle *handle)

{

	/*

	 * Mark the buffer to indicate that there was a WRAP event by

	 * setting the COLLISION flag. This indicates to the user that

	 * the TRBE trace collection was stopped without stopping the

	 * ETE and thus there might be some amount of trace that was

	 * lost between the time the WRAP was detected and the IRQ

	 * was consumed by the CPU.

	 *

	 * Setting the TRUNCATED flag would move the event to STOPPED

	 * state unnecessarily, even when there is space left in the

	 * ring buffer. Using the COLLISION flag doesn't have this side

	 * effect. We only set TRUNCATED flag when there is no space

	 * left in the ring buffer.

	 */

	perf_aux_output_flag(handle, PERF_AUX_FLAG_COLLISION);

}



static void trbe_stop_and_truncate_event(struct perf_output_handle *handle)

static void trbe_stop_and_truncate_event(struct perf_output_handle *handle)

{

{

	struct trbe_buf *buf = etm_perf_sink_config(handle);

	struct trbe_buf *buf = etm_perf_sink_config(handle);
@@ -612,7 +631,7 @@ static unsigned long arm_trbe_update_buffer(struct coresight_device *csdev, 
		 * for correct size. Also, mark the buffer truncated.

		 * for correct size. Also, mark the buffer truncated.

		 */

		 */

		write = get_trbe_limit_pointer();

		write = get_trbe_limit_pointer();

		perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);

		trbe_report_wrap_event(handle);

	}

	}





	offset = write - base;

	offset = write - base;
@@ -708,11 +727,7 @@ static void trbe_handle_overflow(struct perf_output_handle *handle) 
	if (buf->snapshot)

	if (buf->snapshot)

		handle->head += size;

		handle->head += size;





	/*

	trbe_report_wrap_event(handle);

	 * Mark the buffer as truncated, as we have stopped the trace

	 * collection upon the WRAP event, without stopping the source.

	 */

	perf_aux_output_flag(handle, PERF_AUX_FLAG_TRUNCATED);

	perf_aux_output_end(handle, size);

	perf_aux_output_end(handle, size);

	event_data = perf_aux_output_begin(handle, event);

	event_data = perf_aux_output_begin(handle, event);

	if (!event_data) {

	if (!event_data) {