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Subject: Re: [RFC] perf/core: Add an ioctl to get a number of lost samples
To:     Namhyung Kim <namhyung@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
Cc:     Ingo Molnar <mingo@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Stephane Eranian <eranian@google.com>,
        Ian Rogers <irogers@google.com>, gmx@google.com
References: <20210811062135.1332927-1-namhyung@kernel.org>
From:   Andi Kleen <ak@linux.intel.com>
Message-ID: <c857acbf-432e-a9ee-923c-dabc0559a2ff@linux.intel.com>
Date:   Wed, 11 Aug 2021 06:12:04 -0700
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> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index f5a6a2f069ed..44d72079c77a 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -756,6 +756,8 @@ struct perf_event {
>   	struct pid_namespace		*ns;
>   	u64				id;
>   
> +	atomic_t			lost_samples;

Would rather use atomic64_t. atomic_t might wrap too quickly.

But it might be better to put it somewhere where you already have a lock 
on the event, then you wouldn't need an atomic.

-Andi