linux-kernel - Re: [PATCH V3 2/3] coresight: etm: Make cycle count threshold user configurable

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Message-ID: <CAJ9a7Vj5zsOcEQ7QE_T8qPvrciJYcZQqL0U8dp6QkSt-UGynWw@mail.gmail.com>
Date:   Fri, 11 Aug 2023 10:04:23 +0100
From:   Mike Leach <mike.leach@...aro.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, suzuki.poulose@....com,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        James Clark <james.clark@....com>,
        Leo Yan <leo.yan@...aro.org>, Jonathan Corbet <corbet@....net>,
        linux-doc@...r.kernel.org, coresight@...ts.linaro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 2/3] coresight: etm: Make cycle count threshold user configurable

On Fri, 11 Aug 2023 at 09:57, Anshuman Khandual
<anshuman.khandual@....com> wrote:
>
>
>
> On 8/11/23 14:22, Mike Leach wrote:
> > On Fri, 11 Aug 2023 at 04:46, Anshuman Khandual
> > <anshuman.khandual@....com> wrote:
> >>
> >> Cycle counting is enabled, when requested and supported but with a default
> >> threshold value ETM_CYC_THRESHOLD_DEFAULT i.e 0x100 getting into TRCCCCTLR,
> >> representing the minimum interval between cycle count trace packets.
> >>
> >> This makes cycle threshold user configurable, from the user space via perf
> >> event attributes. Although it falls back using ETM_CYC_THRESHOLD_DEFAULT,
> >> in case no explicit request. As expected it creates a sysfs file as well.
> >>
> >> /sys/bus/event_source/devices/cs_etm/format/cc_threshold
> >>
> >> New 'cc_threshold' uses 'event->attr.config3' as no more space is available
> >> in 'event->attr.config1' or 'event->attr.config2'.
> >>
> >> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> >> Cc: Mike Leach <mike.leach@...aro.org>
> >> Cc: James Clark <james.clark@....com>
> >> Cc: Leo Yan <leo.yan@...aro.org>
> >> Cc: coresight@...ts.linaro.org
> >> Cc: linux-arm-kernel@...ts.infradead.org
> >> Cc: linux-doc@...r.kernel.org
> >> Cc: linux-kernel@...r.kernel.org
> >> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> >> ---
> >>  drivers/hwtracing/coresight/coresight-etm-perf.c   |  2 ++
> >>  drivers/hwtracing/coresight/coresight-etm4x-core.c | 12 ++++++++++--
> >>  2 files changed, 12 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> >> index 5ca6278baff4..09f75dffae60 100644
> >> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> >> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> >> @@ -68,6 +68,7 @@ PMU_FORMAT_ATTR(preset,               "config:0-3");
> >>  PMU_FORMAT_ATTR(sinkid,                "config2:0-31");
> >>  /* config ID - set if a system configuration is selected */
> >>  PMU_FORMAT_ATTR(configid,      "config2:32-63");
> >> +PMU_FORMAT_ATTR(cc_threshold,  "config3:0-11");
> >>
> >>
> >>  /*
> >> @@ -101,6 +102,7 @@ static struct attribute *etm_config_formats_attr[] = {
> >>         &format_attr_preset.attr,
> >>         &format_attr_configid.attr,
> >>         &format_attr_branch_broadcast.attr,
> >> +       &format_attr_cc_threshold.attr,
> >>         NULL,
> >>  };
> >>
> >> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> >> index 1f3d29a639ff..ad28ee044cba 100644
> >> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> >> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> >> @@ -644,7 +644,7 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
> >>         struct etmv4_config *config = &drvdata->config;
> >>         struct perf_event_attr *attr = &event->attr;
> >>         unsigned long cfg_hash;
> >> -       int preset;
> >> +       int preset, cc_threshold;
> >>
> >>         /* Clear configuration from previous run */
> >>         memset(config, 0, sizeof(struct etmv4_config));
> >> @@ -667,7 +667,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
> >>         if (attr->config & BIT(ETM_OPT_CYCACC)) {
> >>                 config->cfg |= TRCCONFIGR_CCI;
> >>                 /* TRM: Must program this for cycacc to work */
> >> -               config->ccctlr = ETM_CYC_THRESHOLD_DEFAULT;
> >> +               cc_threshold = attr->config3 & ETM_CYC_THRESHOLD_MASK;
> >> +               if (cc_threshold) {
> >> +                       if (cc_threshold < drvdata->ccitmin)
> >> +                               config->ccctlr = drvdata->ccitmin;
> >> +                       else
> >> +                               config->ccctlr = cc_threshold;
> >> +               } else {
> >> +                       config->ccctlr = ETM_CYC_THRESHOLD_DEFAULT;
> >
> > Don't normally have {} round a single statement else clause - did
>
> I would believe single statement else clause could have { }, only
> when the preceding if clause consists of multiple statements just
> to be symmetrical ?
>
> > checkpatch.pl not object here?
>
> No, it does not object.
>

Fair enough - good to go then!

> >
> >
> > Otherwise
> >
> > Reviewed-by: Mike Leach <mike.leach@...aro.org>
> >
> >> +               }
> >>         }
> >>         if (attr->config & BIT(ETM_OPT_TS)) {
> >>                 /*
> >> --
> >> 2.25.1
> >>
> >
> >



-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK