linux-kernel - Re: [RFC PATCH v1 2/4] drivers/perf: hisi: Add driver support for HiSilicon PMCU

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Date:   Sat, 25 Mar 2023 18:21:59 +0800
From:   Jie Zhan <zhanjie9@...ilicon.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
CC:     <will@...nel.org>, <mark.rutland@....com>,
        <mathieu.poirier@...aro.org>, <suzuki.poulose@....com>,
        <mike.leach@...aro.org>, <leo.yan@...aro.org>,
        <john.g.garry@...cle.com>, <james.clark@....com>,
        <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
        <corbet@....net>, <zhangshaokun@...ilicon.com>,
        <shenyang39@...wei.com>, <hejunhao3@...wei.com>,
        <yangyicong@...ilicon.com>, <prime.zeng@...wei.com>,
        <suntao25@...wei.com>, <jiazhao4@...ilicon.com>,
        <linuxarm@...wei.com>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-perf-users@...r.kernel.org>
Subject: Re: [RFC PATCH v1 2/4] drivers/perf: hisi: Add driver support for
 HiSilicon PMCU



On 17/03/2023 22:52, Jonathan Cameron wrote:
> On Mon, 6 Feb 2023 14:51:44 +0800
> Jie Zhan <zhanjie9@...ilicon.com> wrote:
>
>> HiSilicon Performance Monitor Control Unit (PMCU) is a device that offloads
>> PMU accesses from CPUs, handling the configuration, event switching, and
>> counter reading of core PMUs on Kunpeng SoC. It facilitates fine-grained
>> and multi-PMU-event CPU profiling, in which scenario the current 'perf'
>> scheme may lose events or drop sampling frequency. With PMCU, users can
>> reliably obtain the data of up to 240 PMU events with the sample interval
>> of events down to 1ms, while the software overhead of accessing PMUs, as
>> well as its impact on target workloads, is reduced.
>>
>> This driver enables the usage of PMCU through the perf_event framework.
>> PMCU is registered as a PMU device and utilises the AUX buffer to dump data
>> directly. Users can start PMCU sampling through 'perf-record'. Event
>> numbers are passed by a sysfs interface.
>>
>> Signed-off-by: Jie Zhan <zhanjie9@...ilicon.com>
> Hi Jie,
>
> A few minor comments inline.
> Whilst I looked at this internally, that was a while back so I've
> found a few new things to point out in what I think is a pretty good/clean driver.
> The main thing here is the RFC questions you've raised in the cover letter
> of course - particularly the one around mediating who has the counters between
> this and the normal PMU driver.
>
> Thanks,
>
> Jonathan
Hi Jonathan,

Many thanks for the review again.

Happy to accept all the comments. I have updated the driver based on them.

One reply below.

Jie


...
>> +static const struct attribute_group hisi_pmcu_format_attr_group = {
>> +	.name = "format",
>> +	.attrs = hisi_pmcu_format_attrs,
>> +};
>> +
>> +static ssize_t monitored_cpus_show(struct device *dev,
>> +				   struct device_attribute *attr, char *buf)
>> +{
>> +	struct hisi_pmcu *hisi_pmcu = to_hisi_pmcu(dev_get_drvdata(dev));
>> +
>> +	return sysfs_emit(buf, "%d-%d\n",
>> +			  cpumask_first(&hisi_pmcu->cpus),
>> +			  cpumask_last(&hisi_pmcu->cpus));
> What does this do about offline CPUs?
> Should it include them or not?
PMCU takes care of offline CPUs as well, and the event counts from 
offline CPUs
should show as zeroes in the output.

hisi_pmcu->cpus contains only the online CPUs monitored by the PMCU,
so something should be improved with the "monitored_cpus" interface here.

"monitored_cpus" should actually show alll the online/offline CPUs 
monitored,
or, if it is meant to show only online CPUs, it show be a comma 
separated list
representing the hisi_pmcu->cpus mask rather than a range that may ignore
some offline CPUs in the middle.

Will fix this in V2.