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From:   Shaokun Zhang <zhangshaokun@hisilicon.com>
Subject: [RFC] About perf-mem command support on arm64 platform
To:     <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
CC:     Jiri Olsa <jolsa@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Will Deacon <will@kernel.org>, <liuqi115@hisilicon.com>,
        <huangdaode@hisilicon.com>, <john.garry@huawei.com>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>
Message-ID: <74f8ddb5-13cc-5dce-82a6-ca8bd02f8175@hisilicon.com>
Date:   Mon, 4 Nov 2019 17:18:00 +0800
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Hi all,

perf-mem is used to profile memory access which has been implemented on x86
platform. It needs mem-stores events and mem-loads/load-latency.
For mem-stores events, it is MEM_INST_RETIRED_ALL_STORES whose raw number
is r82d0, and mem-loads/load-latency is from PEBS if I follow its code.

Now, for some arm64 cores, like HiSilicon's tsv110 and ARM's Neoverse N1,
has supported the SPE(Statistical Profiling Extensions), so is it a
possibility that perf-mem is supported on arm64?
https://developer.arm.com/ip-products/processors/neoverse/neoverse-n1

For arm64 PMU, it has 'st_retired' event that the event number is 0x0007
which is equal to mem-stores on x86, if we want support perf-mem, it seems
that 'st_retired' shall be replaced by 'mem-stores'
in arch/arm64/kernel/perf_event.c file. Of course, the cpu core should
support st_retired event. I'm not sure Will/Mark are happy on this.;-)

For mem-loads/load-latency, we can derive them from SPE sampled data which
supports by load_filter and min_latency in SPE driver. and we may do some
work on tools/perf/builtin-mem.c.

From the above conditions, it seems that we may have the opportunity to
support the perf-mem command on arm64.
I'm not very sure about it, so I send this RFC and any comments are welcome.

Thanks,
Shaokun