Messages in this thread Patch in this message | | | From | Leo Yan <> | Subject | [PATCH v3 03/10] coresight: tmc-etf: Add comment for store ordering | Date | Sun, 4 Jul 2021 15:16:37 +0800 |
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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. + */ CS_LOCK(drvdata->base); out: spin_unlock_irqrestore(&drvdata->spinlock, flags); -- 2.25.1
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