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

[Jie Zhan]

On 17/03/2023 22:52, Jonathan Cameron wrote:
> On Mon, 6 Feb 2023 14:51:44 +0800
> Jie Zhan <zhanjie9@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> 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.