Re: [PATCH v2 26/27] coresight: perf: Remove reset_buffer call back for sinks

[Suzuki K Poulose]

On 08/05/18 20:42, Mathieu Poirier wrote:

On Tue, May 01, 2018 at 10:10:56AM +0100, Suzuki K Poulose wrote:

Right now we issue an update_buffer() and reset_buffer() call backs
in succession when we stop tracing an event. The update_buffer is
supposed to check the status of the buffer and make sure the ring buffer
is updated with the trace data. And we store information about the
size of the data collected only to be consumed by the reset_buffer
callback which always follows the update_buffer. This was originally
designed for handling future IPs which could trigger a buffer overflow
interrupt. This patch gets rid of the reset_buffer callback altogether
and performs the actions in update_buffer, making it return the size
collected. We can always add the support for handling the overflow
interrupt case later.

This removes some not-so pretty hack (storing the new head in the
size field for snapshot mode) and cleans it up a little bit.

IPs with an overflow interrupts will be arriving shortly, so it is not like the
future is uncertain - they are coming.  Right now the logic is there - I don't
see a real need to consolidate things only to split it again in the near future.

I agree the part about overloading buf->data_size with the head of the ring
buffer when operating in snapshot mode isn't pretty (though well documented).
If anything that can be improve, i.e add a buf->head and things will be clear.
Once again this could be part of another patchset.

Mathieu,

I am not sure how was this supposed to be used in conjunction with the overflow
handling. Please could you help me here ? I might be able to retain
the callback and possibly improve it with the changes for etr_buf 
infrastructure.

Cheers
Suzuki

Cc: Mathieu Poirier <mathieu.poir...@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poul...@arm.com>
---
  drivers/hwtracing/coresight/coresight-etb10.c    | 56 +++++------------------
  drivers/hwtracing/coresight/coresight-etm-perf.c |  9 +---
  drivers/hwtracing/coresight/coresight-tmc-etf.c  | 58 +++++-------------------
  include/linux/coresight.h                        |  5 +-
  4 files changed, 26 insertions(+), 102 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etb10.c 
b/drivers/hwtracing/coresight/coresight-etb10.c
index d9c2f87..b13712a 100644
--- a/drivers/hwtracing/coresight/coresight-etb10.c
+++ b/drivers/hwtracing/coresight/coresight-etb10.c
@@ -322,37 +322,7 @@ static int etb_set_buffer(struct coresight_device *csdev,
        return ret;
  }

-static unsigned long etb_reset_buffer(struct coresight_device *csdev,

-                                     struct perf_output_handle *handle,
-                                     void *sink_config)
-{
-       unsigned long size = 0;
-       struct cs_buffers *buf = sink_config;
-
-       if (buf) {
-               /*
-                * In snapshot mode ->data_size holds the new address of the
-                * ring buffer's head.  The size itself is the whole address
-                * range since we want the latest information.
-                */
-               if (buf->snapshot)
-                       handle->head = local_xchg(&buf->data_size,
-                                                 buf->nr_pages << PAGE_SHIFT);
-
-               /*
-                * Tell the tracer PMU how much we got in this run and if
-                * something went wrong along the way.  Nobody else can use
-                * this cs_buffers instance until we are done.  As such
-                * resetting parameters here and squaring off with the ring
-                * buffer API in the tracer PMU is fine.
-                */
-               size = local_xchg(&buf->data_size, 0);
-       }
-
-       return size;
-}
-
-static void etb_update_buffer(struct coresight_device *csdev,
+static unsigned long etb_update_buffer(struct coresight_device *csdev,
                              struct perf_output_handle *handle,
                              void *sink_config)
  {
@@ -361,13 +331,13 @@ static void etb_update_buffer(struct coresight_device 
*csdev,
        u8 *buf_ptr;
        const u32 *barrier;
        u32 read_ptr, write_ptr, capacity;
-       u32 status, read_data, to_read;
-       unsigned long offset;
+       u32 status, read_data;
+       unsigned long offset, to_read;
        struct cs_buffers *buf = sink_config;
        struct etb_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);

if (!buf)

-               return;
+               return 0;

capacity = drvdata->buffer_depth * ETB_FRAME_SIZE_WORDS; @@ -472,18 +442,17 @@ static void etb_update_buffer(struct coresight_device *csdev,

        writel_relaxed(0x0, drvdata->base + ETB_RAM_WRITE_POINTER);

/*

-        * In snapshot mode all we have to do is communicate to
-        * perf_aux_output_end() the address of the current head.  In full
-        * trace mode the same function expects a size to move rb->aux_head
-        * forward.
+        * In snapshot mode we have to update the handle->head to point
+        * to the new location.
         */
-       if (buf->snapshot)
-               local_set(&buf->data_size, (cur * PAGE_SIZE) + offset);
-       else
-               local_add(to_read, &buf->data_size);
-
+       if (buf->snapshot) {
+               handle->head = (cur * PAGE_SIZE) + offset;
+               to_read = buf->nr_pages << PAGE_SHIFT;
+       }
        etb_enable_hw(drvdata);
        CS_LOCK(drvdata->base);
+
+       return to_read;
  }

static const struct coresight_ops_sink etb_sink_ops = {

@@ -492,7 +461,6 @@ static const struct coresight_ops_sink etb_sink_ops = {
        .alloc_buffer   = etb_alloc_buffer,
        .free_buffer    = etb_free_buffer,
        .set_buffer     = etb_set_buffer,
-       .reset_buffer   = etb_reset_buffer,
        .update_buffer  = etb_update_buffer,
  };

diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c

index 4e5ed65..5096def 100644
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
@@ -342,15 +342,8 @@ static void etm_event_stop(struct perf_event *event, int 
mode)
                if (!sink_ops(sink)->update_buffer)
                        return;

- sink_ops(sink)->update_buffer(sink, handle,

+               size = sink_ops(sink)->update_buffer(sink, handle,
                                              event_data->snk_config);
-
-               if (!sink_ops(sink)->reset_buffer)
-                       return;
-
-               size = sink_ops(sink)->reset_buffer(sink, handle,
-                                                   event_data->snk_config);
-
                perf_aux_output_end(handle, size);
        }

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c

index 0a32734..75ef5c4 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
@@ -360,36 +360,7 @@ static int tmc_set_etf_buffer(struct coresight_device 
*csdev,
        return ret;
  }

-static unsigned long tmc_reset_etf_buffer(struct coresight_device *csdev,

-                                         struct perf_output_handle *handle,
-                                         void *sink_config)
-{
-       long size = 0;
-       struct cs_buffers *buf = sink_config;
-
-       if (buf) {
-               /*
-                * In snapshot mode ->data_size holds the new address of the
-                * ring buffer's head.  The size itself is the whole address
-                * range since we want the latest information.
-                */
-               if (buf->snapshot)
-                       handle->head = local_xchg(&buf->data_size,
-                                                 buf->nr_pages << PAGE_SHIFT);
-               /*
-                * Tell the tracer PMU how much we got in this run and if
-                * something went wrong along the way.  Nobody else can use
-                * this cs_buffers instance until we are done.  As such
-                * resetting parameters here and squaring off with the ring
-                * buffer API in the tracer PMU is fine.
-                */
-               size = local_xchg(&buf->data_size, 0);
-       }
-
-       return size;
-}
-
-static void tmc_update_etf_buffer(struct coresight_device *csdev,
+static unsigned long tmc_update_etf_buffer(struct coresight_device *csdev,
                                  struct perf_output_handle *handle,
                                  void *sink_config)
  {
@@ -398,17 +369,17 @@ static void tmc_update_etf_buffer(struct coresight_device 
*csdev,
        const u32 *barrier;
        u32 *buf_ptr;
        u64 read_ptr, write_ptr;
-       u32 status, to_read;
-       unsigned long offset;
+       u32 status;
+       unsigned long offset, to_read;
        struct cs_buffers *buf = sink_config;
        struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);

if (!buf)

-               return;
+               return 0;

/* This shouldn't happen */

        if (WARN_ON_ONCE(drvdata->mode != CS_MODE_PERF))
-               return;
+               return 0;

CS_UNLOCK(drvdata->base); @@ -497,18 +468,14 @@ static void tmc_update_etf_buffer(struct coresight_device *csdev,

                }
        }

- /*

-        * In snapshot mode all we have to do is communicate to
-        * perf_aux_output_end() the address of the current head.  In full
-        * trace mode the same function expects a size to move rb->aux_head
-        * forward.
-        */
-       if (buf->snapshot)
-               local_set(&buf->data_size, (cur * PAGE_SIZE) + offset);
-       else
-               local_add(to_read, &buf->data_size);
-
+       /* In snapshot mode we have to update the head */
+       if (buf->snapshot) {
+               handle->head = (cur * PAGE_SIZE) + offset;
+               to_read = buf->nr_pages << PAGE_SHIFT;
+       }
        CS_LOCK(drvdata->base);
+
+       return to_read;
  }

static const struct coresight_ops_sink tmc_etf_sink_ops = {

@@ -517,7 +484,6 @@ static const struct coresight_ops_sink tmc_etf_sink_ops = {
        .alloc_buffer   = tmc_alloc_etf_buffer,
        .free_buffer    = tmc_free_etf_buffer,
        .set_buffer     = tmc_set_etf_buffer,
-       .reset_buffer   = tmc_reset_etf_buffer,
        .update_buffer  = tmc_update_etf_buffer,
  };

diff --git a/include/linux/coresight.h b/include/linux/coresight.h

index c0e1568..41b3729 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -212,10 +212,7 @@ struct coresight_ops_sink {
        int (*set_buffer)(struct coresight_device *csdev,
                          struct perf_output_handle *handle,
                          void *sink_config);
-       unsigned long (*reset_buffer)(struct coresight_device *csdev,
-                                     struct perf_output_handle *handle,
-                                     void *sink_config);
-       void (*update_buffer)(struct coresight_device *csdev,
+       unsigned long (*update_buffer)(struct coresight_device *csdev,
                              struct perf_output_handle *handle,
                              void *sink_config);
  };
--
2.7.4