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Date: Fri, 5 Aug 2016 16:03:30 +0100
From: Mark Rutland <mark.rutland@....com>
To: Zhengyu Shen <zhengyu.shen@....com>
Cc: shawnguo@...nel.org, peterz@...radead.org, frank.li@....com,
linux-kernel@...r.kernel.org, acme@...nel.org,
alexander.shishkin@...ux.intel.com, mingo@...hat.com,
lznuaa@...il.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] Added perf functionality to mmdc driver
On Fri, Aug 05, 2016 at 09:35:25AM -0500, Zhengyu Shen wrote:
> $ perf stat -e mmdc/busy-cycles/,mmdc/read-accesses/,mmdc/read-bytes/,mmdc/total-cycles/,mmdc/write-accesses/,mmdc/write-bytes/ dd if=/dev/zero of=/dev/null bs=1M count=5000
> Performance counter stats for 'dd if=/dev/zero of=/dev/null bs=1M count=5000':
>
> 898021787 mmdc/busy-cycles/
> 14819600 mmdc/read-accesses/
> 471.30 MB mmdc/read-bytes/
> 2815419216 mmdc/total-cycles/
> 13367354 mmdc/write-accesses/
> 427.76 MB mmdc/write-bytes/
>
> 5.334757334 seconds time elapsed
>
As Peter noted, you must better describe this, e.g.
* What is the MMDC (it appears to be a DRAM controller?)
* Which devices have this?
* What types of event does it support?
* Does it have many cuonters? How wide are they? Is there an overflow
interrupt?
* Who is this useful for?
Generally, this looks far from complete, though it's difficult to tell
what the driver should be doing, given the lack of information. Comments
below.
[...]
> +PMU_EVENT_ATTR_STRING(total-cycles, evattr_total_cycles, "event=0x01")
> +PMU_EVENT_ATTR_STRING(busy-cycles, evattr_busy_cycles, "event=0x02")
> +PMU_EVENT_ATTR_STRING(read-accesses, evattr_read_accesses, "event=0x03")
> +PMU_EVENT_ATTR_STRING(write-accesses, evattr_write_accesses, "config=0x04")
> +PMU_EVENT_ATTR_STRING(read-bytes, evattr_read_bytes, "event=0x05")
> +PMU_EVENT_ATTR_STRING(read-bytes.unit, evattr_read_bytes_unit, "MB");
> +PMU_EVENT_ATTR_STRING(read-bytes.scale, evattr_read_bytes_scale, "0.000001");
> +PMU_EVENT_ATTR_STRING(write-bytes, evattr_write_bytes, "event=0x06")
> +PMU_EVENT_ATTR_STRING(write-bytes.unit, evattr_write_bytes_unit, "MB");
> +PMU_EVENT_ATTR_STRING(write-bytes.scale, evattr_write_bytes_scale, "0.000001");
> +
> +struct mmdc_pmu
> +{
> + struct pmu pmu;
> + void __iomem *mmdc_base;
> +};
> +
> +static struct attribute *events_attrs[] = {
> + &evattr_total_cycles.attr.attr,
> + &evattr_busy_cycles.attr.attr,
> + &evattr_read_accesses.attr.attr,
> + &evattr_write_accesses.attr.attr,
> + &evattr_read_bytes.attr.attr,
> + &evattr_read_bytes_unit.attr.attr,
> + &evattr_read_bytes_scale.attr.attr,
> + &evattr_write_bytes.attr.attr,
> + &evattr_write_bytes_unit.attr.attr,
> + &evattr_write_bytes_scale.attr.attr,
> + NULL,
> +};
> +
> +PMU_FORMAT_ATTR(event, "config:0-63");
> +static struct attribute *format_attrs[] = {
> + &format_attr_event.attr,
> + NULL,
> +};
> +
> +static struct attribute_group format_attr_group = {
> + .name = "format",
> + .attrs = format_attrs,
> +};
> +
> +static struct attribute_group events_attr_group = {
> + .name = "events",
> + .attrs = events_attrs,
> +};
> +
> +static const struct attribute_group * attr_groups[] = {
> + &events_attr_group,
> + &format_attr_group,
> + NULL,
> +};
This is an uncore PMU. You need a cpumask file, along with migration
handling.
See drivers/bus/arm-ccn.c for an example.
> +static int mmdc_event_init(struct perf_event *event)
> +{
> + u64 val;
> + if (event->attr.type != event->pmu->type)
> + return -ENOENT;
You *must* validate the event here.
Check the config, grouping, filtering options, etc.
> + mmdc_enable_profiling(event);
> + val = mmdc_read_counter(event);
> + local64_set(&event->hw.prev_count, val);
Are the counters not writable?
> + return 0;
> +}
> +
> +static void mmdc_event_update(struct perf_event * event)
> +{
> + u64 val;
> + val = mmdc_read_counter(event);
> + local64_set(&event->count, val);
> +}
What about prev_count?
> +static void mmdc_event_start(struct perf_event *event, int flags)
> +{
> + mmdc_event_update(event);
> +}
Huh?
Are the counters always-running, with no mechanism to start/stop them?
If so, you must reject event groups, as ratios will be bogus.
> +static int mmdc_event_add(struct perf_event *event, int flags)
> +{
> + if (flags & PERF_EF_START)
> + mmdc_event_start(event, flags);
> + return 0;
> +}
> +
> +static void mmdc_event_stop(struct perf_event *event, int flags)
> +{
> + mmdc_event_update(event);
> +}
> +
> +static void mmdc_event_del(struct perf_event *event, int flags)
> +{
> + mmdc_event_stop(event, PERF_EF_UPDATE);
> +}
> +
> +static void mmdc_pmu_init(struct mmdc_pmu *pmu_mmdc, void __iomem *mmdc_base)
> +{
> + *pmu_mmdc = (struct mmdc_pmu) {
> + .pmu = (struct pmu) {
> + .task_ctx_nr = perf_sw_context,
NAK. This is *not* a softwre PMU. This is a system/uncore PMU, and
should use perf_invalid_context.
> + .attr_groups = attr_groups,
> + .event_init = mmdc_event_init,
> + .add = mmdc_event_add,
> + .del = mmdc_event_del,
> + .start = mmdc_event_start,
> + .stop = mmdc_event_stop,
> + .read = mmdc_event_update,
> + .capabilities = PERF_PMU_CAP_NO_INTERRUPT,
This avoids sampling events, but you still need to poll to account for
overflow.
> + },
> + .mmdc_base = mmdc_base,
> + };
> +}
> +
> static int imx_mmdc_probe(struct platform_device *pdev)
> {
> struct device_node *np = pdev->dev.of_node;
> void __iomem *mmdc_base, *reg;
> + struct mmdc_pmu *pmu_mmdc;
> u32 val;
> int timeout = 0x400;
>
> @@ -61,7 +249,22 @@ static int imx_mmdc_probe(struct platform_device *pdev)
> __func__);
> return -EBUSY;
> }
> + pmu_mmdc = kzalloc(sizeof(struct mmdc_pmu), GFP_KERNEL);
Nit: use sizeof(*pmu_mmdc)
> + if (!pmu_mmdc) {
> + pr_err("failed to allocate PMU device!\n");
> + return -ENOMEM;
> + }
> + mmdc_pmu_init(pmu_mmdc, mmdc_base);
> + platform_set_drvdata(pdev, pmu_mmdc);
> + perf_pmu_register(&(pmu_mmdc->pmu), "mmdc", -1);
> + return 0;
> +}
Thanks,
Mark.
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