On Tue, Jul 13, 2021 at 02:56:06PM +0200, Peter Zijlstra wrote:
On Sun, Jul 11, 2021 at 06:40:57PM +0800, Leo Yan wrote:
AUX ring buffer is required to separate the data store and aux_head store, since the function CS_LOCK() has contained memory barrier mb(), mb() is a more conservative barrier than smp_wmb() on Arm32/Arm64, thus it's needless to add any explicit barrier anymore.
Add comment to make clear for the barrier usage for ETF.
Signed-off-by: Leo Yan leo.yan@linaro.org
drivers/hwtracing/coresight/coresight-tmc-etf.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c index 45b85edfc690..9a42ee689921 100644 --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c @@ -553,6 +553,12 @@ static unsigned long tmc_update_etf_buffer(struct coresight_device *csdev, if (buf->snapshot) handle->head += to_read;
- /*
* AUX ring buffer requires to use memory barrier to separate the trace* data store and aux_head store, because CS_LOCK() contains mb() which* gives more heavy barrier than smp_wmb(), it's not necessary to* explicitly invoke any barrier.*/'more heavy' is not a correctness argument :-)
The argument to make here is that CS_LOCK() ensures completion / visibility of the hardware buffer.
Will correct for this, thanks for reminding!