linux-kernel - Re: [PATCH V4 2/3] coresight: etm: Make cycle count threshold user configurable

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Message-ID: <CAJ9a7Vhg+OznPN_wfVFXgJ9Zx2Y1bCOJZEXpuXK-Ot0JertYyw@mail.gmail.com>
Date:   Fri, 18 Aug 2023 14:01:46 +0100
From:   Mike Leach <mike.leach@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org,
        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 V4 2/3] coresight: etm: Make cycle count threshold user configurable

On Fri, 18 Aug 2023 at 12:25, Suzuki K Poulose <suzuki.poulose@....com> wrote:
>
> On 18/08/2023 12:20, Anshuman Khandual 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
> > Reviewed-by: Mike Leach <mike.leach@...aro.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 591fab73ee79..3193dafa7618 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > @@ -635,7 +635,7 @@ 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));
> > @@ -658,7 +658,15 @@ 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;
>
> Ideally this must be the ccitmin ? Theoretically, default value could be
> bigger than the minimum value supported by the implementation (i.e.,
> ccitmin)
>
> Suzuki
>

In order not to change existing behaviour unexpectedly this could be
re-ordered...

cc_threshold = attr->config3 & ETM_CYC_THRESHOLD_MASK;
if (!cc_threshold)
         cc_threshold = ETM_CYC_THRESHOLD_DEFAULT;
if (cc_threshold < drvdata->ccitmin)
         cc_threshold = drvdata->ccitmin
config->ccctlr = cc_threshold;

Mike
> > +             }
> >       }
> >       if (attr->config & BIT(ETM_OPT_TS)) {
> >               /*
>


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