Date:   Mon, 20 Jun 2022 12:49:57 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Shuai Xue <xueshuai@...ux.alibaba.com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <will@...nel.org>,
        <mark.rutland@....com>, <baolin.wang@...ux.alibaba.com>,
        <yaohongbo@...ux.alibaba.com>, <nengchen@...ux.alibaba.com>,
        <zhuo.song@...ux.alibaba.com>
Subject: Re: [PATCH v1 1/3] docs: perf: Add description for Alibaba's T-Head
 PMU driver

On Fri, 17 Jun 2022 19:18:23 +0800
Shuai Xue <xueshuai@...ux.alibaba.com> wrote:

> Alibaba's T-Head SoC implements uncore PMU for performance and functional
> debugging to facilitate system maintenance. Document it to provide guidance
> on how to use it.
> 
> Signed-off-by: Shuai Xue <xueshuai@...ux.alibaba.com>

Hi Shuia Xue,

A few quick comments inline,

Thanks,

Jonathan

> ---
>  .../admin-guide/perf/alibaba_pmu.rst          | 94 +++++++++++++++++++
>  Documentation/admin-guide/perf/index.rst      |  1 +
>  2 files changed, 95 insertions(+)
>  create mode 100644 Documentation/admin-guide/perf/alibaba_pmu.rst
> 
> diff --git a/Documentation/admin-guide/perf/alibaba_pmu.rst b/Documentation/admin-guide/perf/alibaba_pmu.rst
> new file mode 100644
> index 000000000000..337f4f1d4c54
> --- /dev/null
> +++ b/Documentation/admin-guide/perf/alibaba_pmu.rst
> @@ -0,0 +1,94 @@
> +=============================================================
> +Alibaba's T-Head SoC Uncore Performance Monitoring Unit (PMU)
> +=============================================================
> +
> +The Yitian 710, custom-built by Alibaba Group's chip development business,
> +T-Head, implements uncore PMU for performance and functional debugging to
> +facilitate system maintenance.
> +
> +DDR Sub-System Driveway (DRW) PMU Driver
> +=========================================
> +
> +The Yitian 710 SoC supports the most advanced DDR5/4 DRAM to provide
> +tremendous memory bandwidth for cloud computing and HPC. The Driveway is a
> +module which is a bridge between a router of mesh network and memory
> +controller. It provides various functions like secure control, address map
> +and so on.

I'd focus on the PMU aspect. No point in describing other features in this
document.

> +
> +Yitian 710 employs eight DDR5/4 channels, four on each die. Each channel is
> +independent of others to service system memory requests. And one DDR5

Each DDR5 channel... 

> +channel is split into two independent sub-channels. The DDR Sub-System
> +Driveway implements separate PMUs for each sub-channel to monitor various
> +performance metrics.
> +
> +The Driveway PMU devices are named as ali_drw_<sys_base_addr> with perf.
> +For example, ali_drw_21000 and ali_drw_21080 are two PMU devices for two
> +sub-channels of the same channel in die 0. And the PMU device of die 1 is
> +prefixed with ali_drw_400XXXXX, e.g. ali_drw_40021000.
> +
> +Each sub-channel has 36 PMU counters in total, which is classified into
> +four groups:
> +
> +- Group 0: PMU Cycle Counter. This group has one pair of counters
> +  pmu_cycle_cnt_low and pmu_cycle_cnt_high, that is used as the cycle count
> +  based on DDRC core clock.
> +
> +- Group 1: PMU Bandwidth Counters. This group has 8 counters that are used
> +  to count the total access number of either the eight bank groups in a
> +  selected rank, or four ranks separately in the first 4 counters. The base
> +  transfer unit is 64B.
> +
> +- Group 2: PMU Retry Counters. This group has 10 counters, that intend to
> +  count the total retry number of each type of uncorrectable error.
> +
> +- Group 3: PMU Common Counters. This group has 16 counters, that are used
> +  to count the common events.
> +
> +For now, the Driveway PMU driver only uses counters in group 0 and group 3.
> +
> +Example usage of counting memory data bandwidth::
> +
> +  perf stat \
> +    -e ali_drw_21000/perf_hif_wr/ \

What does hif stand for? Also, perf seems redundant for
a perf event.


> +    -e ali_drw_21000/perf_hif_rd/ \
> +    -e ali_drw_21000/perf_hif_rmw/ \
> +    -e ali_drw_21000/perf_cycle/ \
> +    -e ali_drw_21080/perf_hif_wr/ \
> +    -e ali_drw_21080/perf_hif_rd/ \
> +    -e ali_drw_21080/perf_hif_rmw/ \
> +    -e ali_drw_21080/perf_cycle/ \
> +    -e ali_drw_23000/perf_hif_wr/ \
> +    -e ali_drw_23000/perf_hif_rd/ \
> +    -e ali_drw_23000/perf_hif_rmw/ \
> +    -e ali_drw_23000/perf_cycle/ \
> +    -e ali_drw_23080/perf_hif_wr/ \
> +    -e ali_drw_23080/perf_hif_rd/ \
> +    -e ali_drw_23080/perf_hif_rmw/ \
> +    -e ali_drw_23080/perf_cycle/ \
> +    -e ali_drw_25000/perf_hif_wr/ \
> +    -e ali_drw_25000/perf_hif_rd/ \
> +    -e ali_drw_25000/perf_hif_rmw/ \
> +    -e ali_drw_25000/perf_cycle/ \
> +    -e ali_drw_25080/perf_hif_wr/ \
> +    -e ali_drw_25080/perf_hif_rd/ \
> +    -e ali_drw_25080/perf_hif_rmw/ \
> +    -e ali_drw_25080/perf_cycle/ \
> +    -e ali_drw_27000/perf_hif_wr/ \
> +    -e ali_drw_27000/perf_hif_rd/ \
> +    -e ali_drw_27000/perf_hif_rmw/ \
> +    -e ali_drw_27000/perf_cycle/ \
> +    -e ali_drw_27080/perf_hif_wr/ \
> +    -e ali_drw_27080/perf_hif_rd/ \
> +    -e ali_drw_27080/perf_hif_rmw/ \
> +    -e ali_drw_27080/perf_cycle/ -- sleep 10
> +
> +The average DRAM bandwidth can be calculated as follows:
> +
> +- Read Bandwidth =  perf_hif_rd * DDRC_WIDTH * DDRC_Freq / DDRC_Cycle
> +- Write Bandwidth = (perf_hif_wr + perf_hif_rmw) * DDRC_WIDTH * DDRC_Freq / DDRC_Cycle
> +
> +Here, DDRC_WIDTH = 64 bytes.
> +
> +The current driver does not support sampling. So "perf record" is
> +unsupported.  Also attach to a task is unsupported as the events are all
> +uncore.
> diff --git a/Documentation/admin-guide/perf/index.rst b/Documentation/admin-guide/perf/index.rst
> index 69b23f087c05..bf466ae91c6c 100644
> --- a/Documentation/admin-guide/perf/index.rst
> +++ b/Documentation/admin-guide/perf/index.rst
> @@ -17,3 +17,4 @@ Performance monitor support
>     xgene-pmu
>     arm_dsu_pmu
>     thunderx2-pmu
> +   thead_pmu

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