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Date:   Thu, 14 Feb 2019 08:26:13 -0800
From:   Andi Kleen <ak@linux.intel.com>
To:     Wei Wang <wei.w.wang@intel.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        pbonzini@redhat.com, peterz@infradead.org, kan.liang@intel.com,
        mingo@redhat.com, rkrcmar@redhat.com, like.xu@intel.com,
        jannh@google.com, arei.gonglei@huawei.com, jmattson@google.com
Subject: Re: [PATCH v5 07/12] perf/x86: no counter allocation support
Message-ID: <20190214162613.GK16922@tassilo.jf.intel.com>
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> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 9de8780..ec97a70 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -372,7 +372,8 @@ struct perf_event_attr {
>  				context_switch :  1, /* context switch data */
>  				write_backward :  1, /* Write ring buffer from end to beginning */
>  				namespaces     :  1, /* include namespaces data */
> -				__reserved_1   : 35;
> +				no_counter     :  1, /* no counter allocation */

Not sure we really want to expose this in the user ABI. Perhaps make
it a feature of the in kernel API only?

-Andi