linux-kernel - Re: [PATCH V4 4/7] perf/x86/intel: Support LBR event logging

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Message-ID: <20231019110056.GH36211@noisy.programming.kicks-ass.net>
Date:   Thu, 19 Oct 2023 13:00:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
Cc:     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, ak@...ux.intel.com, eranian@...gle.com,
        alexey.v.bayduraev@...ux.intel.com, tinghao.zhang@...el.com
Subject: Re: [PATCH V4 4/7] perf/x86/intel: Support LBR event logging

On Wed, Oct 04, 2023 at 11:40:41AM -0700, kan.liang@...ux.intel.com wrote:

> +static ssize_t branch_counter_width_show(struct device *cdev,
> +					 struct device_attribute *attr,
> +					 char *buf)
> +{
> +	return snprintf(buf, PAGE_SIZE, "2\n");
> +}

> +#define ARCH_LBR_EVENT_LOG_WIDTH	2

I'm assuming this is the same '2' ? And having it hard-coded in two
locations is awesome..

> +#define ARCH_LBR_EVENT_LOG_MASK		0x3

Should probably be ((1<<2)-1)

As per that other email, the naming is confusing, should this not be:

ARCH_LBR_EVENT_COUNTER_BITS

or, since it's all local to lbr.c something shorter still, like:

LBR_COUNTER_BITS

hmm?