linux-kernel - Re: [PATCH v2 2/4] perf arm_arch_timer: Convert between counter and timestamp

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Date:   Thu, 20 Aug 2020 11:05:17 +0800
From:   "liwei (GF)" <liwei391@...wei.com>
To:     Leo Yan <leo.yan@...aro.org>
CC:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ian Rogers <irogers@...gle.com>, Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Kemeng Shi <shikemeng@...wei.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Igor Lubashev <ilubashe@...mai.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        James Clark <james.clark@....com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] perf arm_arch_timer: Convert between counter and
 timestamp

Hi Leo,

On 2020/8/7 15:16, Leo Yan wrote:
> This patch introduces two new APIs, one is to calculate from converting
> counter to timestamp and provides a reverse flow to convert timestamp
> to counter.
> 
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> ---
>  tools/perf/util/Build            |  1 +
>  tools/perf/util/arm_arch_timer.c | 28 ++++++++++++++++++++++++++++
>  tools/perf/util/arm_arch_timer.h |  3 +++
>  3 files changed, 32 insertions(+)
>  create mode 100644 tools/perf/util/arm_arch_timer.c
> 
> diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> index 8d18380ecd10..ba504549844f 100644
> --- a/tools/perf/util/Build
> +++ b/tools/perf/util/Build
> @@ -101,6 +101,7 @@ perf-y += call-path.o
>  perf-y += rwsem.o
>  perf-y += thread-stack.o
>  perf-y += spark.o
> +perf-y += arm_arch_timer.o
>  perf-$(CONFIG_AUXTRACE) += auxtrace.o
>  perf-$(CONFIG_AUXTRACE) += intel-pt-decoder/
>  perf-$(CONFIG_AUXTRACE) += intel-pt.o
> diff --git a/tools/perf/util/arm_arch_timer.c b/tools/perf/util/arm_arch_timer.c
> new file mode 100644
> index 000000000000..c37ffa4d9710
> --- /dev/null
> +++ b/tools/perf/util/arm_arch_timer.c
> @@ -0,0 +1,28 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/compiler.h>
> +#include <linux/types.h>
> +
> +#include "arm_arch_timer.h"
> +
> +u64 perf_time_to_arch_timer_cyc(u64 ns, struct perf_arch_timer_conversion *tc)
> +{
> +	u64 t, quot, rem;
> +
> +	t = ns - tc->time_zero;
> +	quot = t / tc->time_mult;
> +	rem  = t % tc->time_mult;
> +	return (quot << tc->time_shift) +
> +	       (rem << tc->time_shift) / tc->time_mult;
> +}
> +
> +u64 arch_timer_cyc_to_perf_time(u64 cyc, struct perf_arch_timer_conversion *tc)
> +{
> +	u64 quot, rem;
> +
> +	cyc = tc->time_cycles + ((cyc - tc->time_cycles) & tc->time_mask);
> +
> +	quot = cyc >> tc->time_shift;
> +	rem  = cyc & (((u64)1 << tc->time_shift) - 1);
> +	return tc->time_zero + quot * tc->time_mult +
> +	       ((rem * tc->time_mult) >> tc->time_shift);
> +}

Can we merge these methods with 'tools/perf/util/tsc.c'?  I think the converting
between arch timestamp and the perf time should be arch independent. And in fact, we
have built tsc_to_perf_time() into the perf on arm64. So maybe we can add
cap_user_time_xxx into 'struct perf_tsc_conversion', then dispatch for different
capabilities.

Thanks,
Wei

> diff --git a/tools/perf/util/arm_arch_timer.h b/tools/perf/util/arm_arch_timer.h
> index a3263cc4e5cf..7d9271f544f2 100644
> --- a/tools/perf/util/arm_arch_timer.h
> +++ b/tools/perf/util/arm_arch_timer.h
> @@ -17,4 +17,7 @@ struct perf_event_mmap_page;
>  int perf_read_arch_timer_conversion(const struct perf_event_mmap_page *pc,
>  				    struct perf_arch_timer_conversion *tc);
>  
> +u64 arch_timer_cyc_to_perf_time(u64 cyc, struct perf_arch_timer_conversion *tc);
> +u64 perf_time_to_arch_timer_cyc(u64 ns, struct perf_arch_timer_conversion *tc);
> +
>  #endif // __PERF_ARM_ARCH_TIMER_H
>