linux-kernel - Re: [PATCH v1 1/3] docs: perf: Add description for Alibaba's T-Head PMU driver

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Message-ID: <4de128c7-4dec-6bb2-737e-656f5ab4ea8d@linux.alibaba.com>
Date:   Thu, 23 Jun 2022 16:34:40 +0800
From:   Shuai Xue <xueshuai@...ux.alibaba.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.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


在 2022/6/20 PM7:49, Jonathan Cameron 写道:
> 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

Hi, Jonathan,

Thank you very much for your quick comments.

> 
>> ---
>>  .../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.

Got it. I will delete this in next version.

>> +
>> +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... 

Good catch, I will declare as 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.

HIF stands for Host Interface which is a Synopsys’ custom-defined interface.
On the host side, there is a choice of an AMBA 4 AXI interface or a
custom Host Interface (HIF). The AMBA interface supports single or multi-port
configurations, while the HIF supports a single port only. Read, write, and
RMW requests as well as write data are received through the HIF. I will doc
this in next version.

The `perf` prefix means Performance Logging Signals in DDRC, I will remove it
in next version.

>> +    -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