linux-kernel - Re: [PATCH 2/6] perf: Support branch events logging

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Message-ID: <20230417114654.GL83892@hirez.programming.kicks-ass.net>
Date:   Mon, 17 Apr 2023 13:46:54 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     "Liang, Kan" <kan.liang@...ux.intel.com>, mingo@...hat.com,
        acme@...nel.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...nel.org, namhyung@...nel.org, irogers@...gle.com,
        adrian.hunter@...el.com, eranian@...gle.com
Subject: Re: [PATCH 2/6] perf: Support branch events logging

On Fri, Apr 14, 2023 at 03:47:29PM -0700, Andi Kleen wrote:
> 
> > Yeah, don't do this. There is no guarantee what so ever you'll get any
> > of those events in the 0-3 range.
> 
> 
> The kernel can simply force to 0-3 if LBR is enabled and the feature too.
> It's in Kan's patch
> 
> and it isn't particularly complicated.

And what, totally leave 4-7 unused even if those counters were not
related to LBR at all? That seems exceedingly daft.