linux-kernel - Re: [PATCH 2/3] perf/amlogic: Fix large number of counter issue

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Date:   Tue, 28 Mar 2023 10:29:04 +0800
From:   Jiucheng Xu <jiuchengxu@....com>
To:     Will Deacon <will@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Jianxin Pan <jianxin.pan@...ogic.com>,
        Kelvin Zhang <kelvin.zhang@...ogic.com>,
        Chris Healy <cphealy@...il.com>,
        Chris Healy <healych@...zon.com>,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] perf/amlogic: Fix large number of counter issue


My Amlogic email box has some issues. Use my personal email 
<jiucheng.xu@....com> to reply.

On 2023/3/27 22:10, Will Deacon wrote:
> [ EXTERNAL EMAIL ]
>
> On Thu, Feb 09, 2023 at 07:54:02PM +0800, Jiucheng Xu wrote:
>> When use 1ms interval, very large number of counter happens
>> once in a while as below:
>>
>> 25.968654513 281474976710655.84 MB meson_ddr_bw/chan_1_rw_bytes,arm=1/
>> 26.118657346 281474976710655.88 MB meson_ddr_bw/chan_1_rw_bytes,arm=1/
>> 26.180137180 281474976710655.66 MB meson_ddr_bw/chan_1_rw_bytes,arm=1/
>>
>> Root cause is the race between irq handler
>> and pmu.read callback. Use spin lock to protect the sw&hw
>> counters.
>>
>> Signed-off-by: Jiucheng Xu <jiucheng.xu@...ogic.com>
>> ---
>>   drivers/perf/amlogic/meson_ddr_pmu_core.c | 10 +++++++++-
>>   1 file changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/perf/amlogic/meson_ddr_pmu_core.c b/drivers/perf/amlogic/meson_ddr_pmu_core.c
>> index 0b24dee1ed3c..9b2e5d5c0626 100644
>> --- a/drivers/perf/amlogic/meson_ddr_pmu_core.c
>> +++ b/drivers/perf/amlogic/meson_ddr_pmu_core.c
>> @@ -14,6 +14,7 @@
>>   #include <linux/perf_event.h>
>>   #include <linux/platform_device.h>
>>   #include <linux/printk.h>
>> +#include <linux/spinlock.h>
>>   #include <linux/sysfs.h>
>>   #include <linux/types.h>
>>   
>> @@ -23,6 +24,7 @@ struct ddr_pmu {
>>   	struct pmu pmu;
>>   	struct dmc_info info;
>>   	struct dmc_counter counters;	/* save counters from hw */
>> +	spinlock_t lock;		/* protect hw/sw counter */
>>   	bool pmu_enabled;
>>   	struct device *dev;
>>   	char *name;
>> @@ -92,10 +94,12 @@ static void meson_ddr_perf_event_update(struct perf_event *event)
>>   	int idx;
>>   	int chann_nr = pmu->info.hw_info->chann_nr;
>>   
>> +	spin_lock(&pmu->lock);
> Why doesn't this need the _irqsave() variant if we're racing with the irq
> handler?
>
> Will
I think meson_ddr_perf_event_update function is called with hard irq off.
So update function couldn't be interrupted by irq handler. Right?

Thanks,
Jiucheng
>