On 26 January 2016 at 08:53, Alexander Shishkin
<alexander.shishkin@xxxxxxxxxxxxxxx> wrote:
> Mathieu Poirier <mathieu.poirier@xxxxxxxxxx> writes:
>
>> Adding an ETB10 specific AUX area operations to be used
>> by the perf framework when events are initialised.
>>
>> Part of this operation involves modeling the mmap'ed area
>> based on the specific ways a sink buffer gathers information.
>
> I don't mind being CC'd on the rest of the patches too, btw. :)
Most definitely.
>
>> +static unsigned long etb_reset_buffer(struct coresight_device *csdev,
>> + struct perf_output_handle *handle,
>> + void *sink_config, bool *lost)
>> +{
>> + 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.
>> + */
>> + *lost = local_xchg(&buf->lost, 0);
>
> This is a thin ice, you can't really make assumptions about bool's
> storage size or even type, afaict.
You are theoretically correct but I wonder if the value of &buf->lost
can get to a size where it won't fit in *lost... Nevertheless I'll fix
it with:
*lost = !!local_xchg(&buf->lost, 0);
>
>> + size = local_xchg(&buf->data_size, 0);
>> + }
>> +
>> + return size;
>> +}
>> +
>> +static void etb_update_buffer(struct coresight_device *csdev,
>> + struct perf_output_handle *handle,
>> + void *sink_config)
>> +{
>> + int i, cur;
>> + u8 *buf_ptr;
>> + u32 read_ptr, write_ptr, capacity;
>> + u32 status, read_data, to_read;
>> + unsigned long flags, offset;
>> + struct cs_buffers *buf = sink_config;
>> + struct etb_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>> +
>> + if (!buf)
>> + return;
>> +
>> + capacity = drvdata->buffer_depth * ETB_FRAME_SIZE_WORDS;
>> +
>> + spin_lock_irqsave(&drvdata->spinlock, flags);
>
> This spinlock seems to be held over the entire readout operation,
> however, I can't find clear rules wrt what structures etc are serialized
> on it. Instead, the comment says "only one at a time pls". Same for
> etm's big drvdata spinlock.
That spinlock is there to serialise actions coming from sysFS. I
originally added the spinlock to 'etb_update_buffer()' to guard
against reading the internal RAM buffer from sysfs while a perf
session is active. But after supplementing 'etb_dump()' with 'mode'
awareness this spinlock it is no longer required.
>
> Regards,
> --
> Alex
--
To unsubscribe from this list: send the line "unsubscribe linux-doc" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
