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Message-ID: <CAKTKpr7juHd9Bgam28LESadihFadEAevRAhc-7w3PTMYY7HLNw@mail.gmail.com>
Date: Tue, 13 Aug 2019 16:25:15 +0530
From: Ganapatrao Kulkarni <gklkml16@...il.com>
To: Mark Rutland <mark.rutland@....com>
Cc: Ganapatrao Kulkarni <gkulkarni@...vell.com>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"will@...nel.org" <will@...nel.org>,
"corbet@....net" <corbet@....net>,
Jayachandran Chandrasekharan Nair <jnair@...vell.com>,
Robert Richter <rrichter@...vell.com>,
Jan Glauber <jglauber@...vell.com>
Subject: Re: [PATCH v3 2/2] drivers/perf: Add CCPI2 PMU support in ThunderX2
UNCORE driver.
Hi Mark,
On Mon, Aug 12, 2019 at 5:31 PM Mark Rutland <mark.rutland@....com> wrote:
>
> On Tue, Jul 23, 2019 at 09:16:28AM +0000, Ganapatrao Kulkarni wrote:
> > CCPI2 is a low-latency high-bandwidth serial interface for connecting
> > ThunderX2 processors. This patch adds support to capture CCPI2 perf events.
>
> It would be worth pointing out in the commit message how the CCPI2
> counters differ from the others. I realise you have that in the body of
> patch 1, but it's critical information when reviewing this patch...
Ok, I will add in next version.
>
> >
> > Signed-off-by: Ganapatrao Kulkarni <gkulkarni@...vell.com>
> > ---
> > drivers/perf/thunderx2_pmu.c | 248 ++++++++++++++++++++++++++++++-----
> > 1 file changed, 214 insertions(+), 34 deletions(-)
> >
> > diff --git a/drivers/perf/thunderx2_pmu.c b/drivers/perf/thunderx2_pmu.c
> > index 43d76c85da56..a4e1273eafa3 100644
> > --- a/drivers/perf/thunderx2_pmu.c
> > +++ b/drivers/perf/thunderx2_pmu.c
> > @@ -17,22 +17,31 @@
> > */
> >
> > #define TX2_PMU_MAX_COUNTERS 4
>
> Shouldn't this be 8 now?
It is kept unchanged to 4(as suggested by Will), which is same for
both L3 and DMC.
For CCPI2 this macro is not used.
>
> [...]
>
> > /*
> > - * pmu on each socket has 2 uncore devices(dmc and l3c),
> > - * each device has 4 counters.
> > + * pmu on each socket has 3 uncore devices(dmc, l3ci and ccpi2),
> > + * dmc and l3c has 4 counters and ccpi2 8.
> > */
>
> How about:
>
> /*
> * Each socket has 3 uncore device associated with a PMU. The DMC and
> * L3C have 4 32-bit counters, and the CCPI2 has 8 64-bit counters.
> */
Thanks.
>
> > struct tx2_uncore_pmu {
> > struct hlist_node hpnode;
> > @@ -69,12 +86,14 @@ struct tx2_uncore_pmu {
> > int node;
> > int cpu;
> > u32 max_counters;
> > + u32 counters_mask;
> > u32 prorate_factor;
> > u32 max_events;
> > + u32 events_mask;
> > u64 hrtimer_interval;
> > void __iomem *base;
> > DECLARE_BITMAP(active_counters, TX2_PMU_MAX_COUNTERS);
>
> This bitmap isn't big enough for the 4 new counters.
>
> > - struct perf_event *events[TX2_PMU_MAX_COUNTERS];
> > + struct perf_event **events;
>
> As above, can't we bump TX2_PMU_MAX_COUNTERS to 8 rather than making
> this a dynamic allocation?
events is only relevant for L3 and DMC since they use timer callbacks.
This is done as per previous review comments.
>
> [...]
>
> > static inline u32 reg_readl(unsigned long addr)
> > {
> > return readl((void __iomem *)addr);
> > }
> >
> > +static inline u32 reg_readq(unsigned long addr)
> > +{
> > + return readq((void __iomem *)addr);
> > +}
>
> Presumably reg_readq() should return a u64.
Yes, My bad.
>
> [...]
>
> > +static void uncore_start_event_ccpi2(struct perf_event *event, int flags)
> > +{
> > + u32 emask;
> > + struct hw_perf_event *hwc = &event->hw;
> > + struct tx2_uncore_pmu *tx2_pmu;
> > +
> > + tx2_pmu = pmu_to_tx2_pmu(event->pmu);
> > + emask = tx2_pmu->events_mask;
> > +
> > + /* Bit [09:00] to set event id, set level and type to 1 */
> > + reg_writel((3 << 10) |
>
> Do you mean that bits [11:10] are level and type?
Yes, i will change the comment.
>
> What exactly are 'level' and 'type'?
They are for other settings which are not relevant for software/kernel.
>
> Can we give those bits mnemonics?
>
> > + GET_EVENTID(event, emask), hwc->config_base);
> > + /* reset[4], enable[0] and start[1] counters */
>
> Rather than using magic numbers everywhere, please give these mnemonics,
> e.g.
>
> #define CCPI2_PERF_CTL_ENABLE BIT(0)
> #define CCPI2_PERF_CTL_START BIT(1)
> #define CCPI2_PERF_CTL_RESET BIT(4)
not used everywhere, only in this function.
I can add these macros.
>
> > + reg_writel(0x13, hwc->event_base + CCPI2_PERF_CTL);
>
> ... and then you can OR them in here:
OK
>
> ctl = CCPI2_PERF_CTL_ENABLE |
> CCPI2_PERF_CTL_START |
> CCPI2_PERF_CTL_RESET;
> reg_writel(ctl, hwc->event_base + CCPI2_PERF_CTL);
>
> [...]
>
> > @@ -456,8 +603,9 @@ static void tx2_uncore_event_start(struct perf_event *event, int flags)
> > tx2_pmu->start_event(event, flags);
> > perf_event_update_userpage(event);
> >
> > - /* Start timer for first event */
> > - if (bitmap_weight(tx2_pmu->active_counters,
> > + /* Start timer for first non ccpi2 event */
> > + if (tx2_pmu->type != PMU_TYPE_CCPI2 &&
> > + bitmap_weight(tx2_pmu->active_counters,
> > tx2_pmu->max_counters) == 1) {
> > hrtimer_start(&tx2_pmu->hrtimer,
> > ns_to_ktime(tx2_pmu->hrtimer_interval),
>
> This would be easier to read as two statements:
>
> /* No hrtimer needed with 64-bit counters */
> if (tx2_pmu->type == PMU_TYPE_CCPI2)
> return;
>
> /* Start timer for first event */
> if (bitmap_weight(tx2_pmu->active_counters,
> tx2_pmu->max_counters) != 1) {
> ...
> }
>
OK, makes sense.
> > @@ -495,7 +643,8 @@ static int tx2_uncore_event_add(struct perf_event *event, int flags)
> > if (hwc->idx < 0)
> > return -EAGAIN;
> >
> > - tx2_pmu->events[hwc->idx] = event;
> > + if (tx2_pmu->events)
> > + tx2_pmu->events[hwc->idx] = event;
>
> So this is NULL for CCPI2?
Yes.
>
> I guess we don't strictly need the if we don't have a hrtimer to update
> event counts, but this makes the code more complicated than it needs to
> be.
Yes I am using tx2_pmu->events to differentiate the type, it is NULL for CCPI2.
I can extend same to tx2_uncore_event_start().
>
> [...]
>
> > @@ -580,8 +732,12 @@ static int tx2_uncore_pmu_add_dev(struct tx2_uncore_pmu *tx2_pmu)
> > cpu_online_mask);
> >
> > tx2_pmu->cpu = cpu;
> > - hrtimer_init(&tx2_pmu->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> > - tx2_pmu->hrtimer.function = tx2_hrtimer_callback;
> > + /* CCPI2 counters are 64 bit counters, no overflow */
> > + if (tx2_pmu->type != PMU_TYPE_CCPI2) {
> > + hrtimer_init(&tx2_pmu->hrtimer,
> > + CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> > + tx2_pmu->hrtimer.function = tx2_hrtimer_callback;
> > + }
>
> Hmmm... this means that tx2_pmu->hrtimer.function is NULL for the CCPI2
> PMU. I think it would be best to check that when (re)programming the
> counters rather than the PMU type. For example, in
> tx2_uncore_event_start() we could have:
>
> if (!tx2_pmu->hrtimer.function)
> return;
> if (bitmap_weight(tx2_pmu->active_counters,
> tx2_pmu->max_counters) != 1) {
> ...
> }
>
Yes it is NULL for CCPI2.
Ok, I can use tx2_pmu->events instead(like other places).
> Thanks,
> Mark.
Thanks,
Ganapat
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