Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:7 as permitted sender) client-ip=2620:137:e000::3:7;
Date:   Thu, 19 Oct 2023 13:12:02 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     kan.liang@linux.intel.com
Cc:     mingo@redhat.com, acme@kernel.org, linux-kernel@vger.kernel.org,
        mark.rutland@arm.com, alexander.shishkin@linux.intel.com,
        jolsa@kernel.org, namhyung@kernel.org, irogers@google.com,
        adrian.hunter@intel.com, ak@linux.intel.com, eranian@google.com,
        alexey.v.bayduraev@linux.intel.com, tinghao.zhang@intel.com
Subject: Re: [PATCH V4 4/7] perf/x86/intel: Support LBR event logging
Message-ID: <20231019111202.GJ36211@noisy.programming.kicks-ass.net>
References: <20231004184044.3062788-1-kan.liang@linux.intel.com>
 <20231004184044.3062788-4-kan.liang@linux.intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20231004184044.3062788-4-kan.liang@linux.intel.com>
Precedence: bulk

On Wed, Oct 04, 2023 at 11:40:41AM -0700, kan.liang@linux.intel.com wrote:
> +static __always_inline void get_lbr_events(struct cpu_hw_events *cpuc,
> +					   int i, u64 info)
> +{
> +	/*
> +	 * The later code will decide what content can be disclosed
> +	 * to the perf tool. It's no harmful to unconditionally update
> +	 * the cpuc->lbr_events.
> +	 * Pleae see intel_pmu_lbr_event_reorder()
> +	 */
> +	cpuc->lbr_events[i] = info & LBR_INFO_EVENTS;
> +}

You could be forcing an extra cachemiss here. A long time ago I had
hacks to profile perf with perf, but perhaps PT can be abused for that
now?