linux-kernel - Re: [PATCH v6 4/5] perf: CXL Performance Monitoring Unit driver

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Message-ID: <20230423144801.00006efd@Huawei.com>
Date:   Sun, 23 Apr 2023 14:48:01 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Dan Williams <dan.j.williams@...el.com>
CC:     Liang Kan <kan.liang@...ux.intel.com>, <linux-cxl@...r.kernel.org>,
        <peterz@...radead.org>, <mark.rutland@....com>, <will@...nel.org>,
        <mingo@...hat.com>, <acme@...nel.org>, <linuxarm@...wei.com>,
        <linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Dave Jiang <dave.jiang@...el.com>
Subject: Re: [PATCH v6 4/5] perf: CXL Performance Monitoring Unit driver

On Sat, 22 Apr 2023 15:31:18 -0700
Dan Williams <dan.j.williams@...el.com> wrote:

> Jonathan Cameron wrote:
> > CXL rev 3.0 introduces a standard performance monitoring hardware
> > block to CXL. Instances are discovered using CXL Register Locator DVSEC
> > entries. Each CXL component may have multiple PMUs.
> > 
> > This initial driver supports a subset of types of counter.
> > It supports counters that are either fixed or configurable, but requires
> > that they support the ability to freeze and write value whilst frozen.
> > 
> > Development done with QEMU model which will be posted shortly.
> > 
> > Example:
> > 
> > $ perf stat -e cxl_pmu_mem0.0/h2d_req_snpcur/ -e cpmu0/h2d_req_snpdata/ -e cpmu0/clock_ticks/ sleep 1
> > 
> > Performance counter stats for 'system wide':
> > 
> > 96,757,023,244,321      cxl_pmu_mem0.0/h2d_req_snpcur/
> > 96,757,023,244,365      cxl_pmu_mem0.0/h2d_req_snpdata/
> > 193,514,046,488,653      cxl_pmu_mem0.0/clock_ticks/
> > 
> >        1.090539600 seconds time elapsed
> > 
> > Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> > Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>  
> 
> Jonathan, I was awaiting a "perf maintainer ack" before applying this,
> only to now realize there is no maintainer entry for drivers/perf/ in
> general, only "ARM PMU PROFILING AND DEBUGGING". Were you waiting on any
> additional acks from perf folks for this?

I'm always hopeful.  For everything similar we've done in the past in
drivers/perf, Will Deacon has taken a look and ultimately taken the series
(often Mark has as well), but then those drivers could be very loosely
termed ARM PMU on basis they happen to be PMUs on an ARM architecture
system even if they have nothing at all to do with the ARM architecture
itself (e.g. our PCI PMUs).

I see the riscv stuff has been going in drivers/perf without an Ack from
them though so there is precedent for non ARM stuff in this directory
going in through other trees despite the catch all maintainers entry.

So, Will / Mark do you consider this in your maintainer scope? 

Your input is welcome either way but as you might be very busy I
don't want to commit you to taking a look at this CXL driver.

> 
> If there are no objections I think this can be included in the back half
> of the merge window for v6.4, as it stands now I was still awaiting the
> final go ahead.

That would be great if possible. If not I'll just back new features up
behind this series and hopefully a larger set might go in next cycle.

Thanks,

Jonathan