linux-kernel - Re: [PATCH v4 2/2] ThunderX2: Add Cavium ThunderX2 SoC UNCORE PMU driver

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Date:   Mon, 21 May 2018 18:12:07 +0530
From:   Ganapatrao Kulkarni <gklkml16@...il.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Ganapatrao Kulkarni <ganapatrao.kulkarni@...ium.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Will Deacon <Will.Deacon@....com>, jnair@...iumnetworks.com,
        Robert Richter <Robert.Richter@...ium.com>,
        Vadim.Lomovtsev@...ium.com, Jan.Glauber@...ium.com
Subject: Re: [PATCH v4 2/2] ThunderX2: Add Cavium ThunderX2 SoC UNCORE PMU driver

On Mon, May 21, 2018 at 4:10 PM, Mark Rutland <mark.rutland@....com> wrote:
> On Mon, May 21, 2018 at 11:37:12AM +0100, Mark Rutland wrote:
>> Hi Ganapat,
>>
>>
>> Sorry for the delay in replying; I was away most of last week.
>>
>> On Tue, May 15, 2018 at 04:03:19PM +0530, Ganapatrao Kulkarni wrote:
>> > On Sat, May 5, 2018 at 12:16 AM, Ganapatrao Kulkarni <gklkml16@...il.com> wrote:
>> > > On Thu, Apr 26, 2018 at 4:29 PM, Mark Rutland <mark.rutland@....com> wrote:
>> > >> On Wed, Apr 25, 2018 at 02:30:47PM +0530, Ganapatrao Kulkarni wrote:
>>
>> > >>> +static int alloc_counter(struct thunderx2_pmu_uncore_channel *pmu_uncore)
>> > >>> +{
>> > >>> +     int counter;
>> > >>> +
>> > >>> +     raw_spin_lock(&pmu_uncore->lock);
>> > >>> +     counter = find_first_zero_bit(pmu_uncore->counter_mask,
>> > >>> +                             pmu_uncore->uncore_dev->max_counters);
>> > >>> +     if (counter == pmu_uncore->uncore_dev->max_counters) {
>> > >>> +             raw_spin_unlock(&pmu_uncore->lock);
>> > >>> +             return -ENOSPC;
>> > >>> +     }
>> > >>> +     set_bit(counter, pmu_uncore->counter_mask);
>> > >>> +     raw_spin_unlock(&pmu_uncore->lock);
>> > >>> +     return counter;
>> > >>> +}
>> > >>> +
>> > >>> +static void free_counter(struct thunderx2_pmu_uncore_channel *pmu_uncore,
>> > >>> +                                     int counter)
>> > >>> +{
>> > >>> +     raw_spin_lock(&pmu_uncore->lock);
>> > >>> +     clear_bit(counter, pmu_uncore->counter_mask);
>> > >>> +     raw_spin_unlock(&pmu_uncore->lock);
>> > >>> +}
>> > >>
>> > >> I don't believe that locking is required in either of these, as the perf
>> > >> core serializes pmu::add() and pmu::del(), where these get called.
>> >
>> > without this locking, i am seeing "BUG: scheduling while atomic" when
>> > i run perf with more events together than the maximum counters
>> > supported
>>
>> Did you manage to get to the bottom of this?
>>
>> Do you have a backtrace?
>>
>> It looks like in your latest posting you reserve counters through the
>> userspace ABI, which doesn't seem right to me, and I'd like to
>> understand the problem.
>
> Looks like I misunderstood -- those are still allocated kernel-side.
>
> I'll follow that up in the v5 posting.

please review v5.
>
> Thanks,
> Mark.

thanks
Ganapat