linux-kernel - Re: [PATCH 1/6] perf cs-etm: Refactor initialisation of kernel start address

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Date:   Mon, 19 Jul 2021 13:37:52 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     James Clark <james.clark@....com>
Cc:     acme@...nel.org, coresight@...ts.linaro.org, leo.yan@...aro.org,
        al.grant@....com, branislav.rankov@....com, suzuki.poulose@....com,
        anshuman.khandual@....com, Mike Leach <mike.leach@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] perf cs-etm: Refactor initialisation of kernel start
 address

On Tue, Jul 13, 2021 at 04:40:03PM +0100, James Clark wrote:
> The kernel start address is already cached in the machine struct once it
> is initialised, so storing it in the cs_etm struct is unnecessary.
> 
> It also depends on kernel maps being available to be initialised.
> Therefore cs_etm__setup_queues() isn't an appropriate place to call it
> because it could be called before processing starts. It would be better
> to initialise it at the point when it is needed, then we can be sure
> that all the necessary maps are available. Also by calling
> machine__kernel_start() multiple times it can be initialised at some
> point, even if it failed to initialise previously due to missing maps.
> 
> In a later commit cs_etm__setup_queues() will be moved which is the
> motivation for this change.
> 
> Signed-off-by: James Clark <james.clark@....com>

Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>

> ---
>  tools/perf/util/cs-etm.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index bc1f64873c8f..4c69ef391f60 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -62,7 +62,6 @@ struct cs_etm_auxtrace {
>  	u64 instructions_sample_period;
>  	u64 instructions_id;
>  	u64 **metadata;
> -	u64 kernel_start;
>  	unsigned int pmu_type;
>  };
>  
> @@ -691,7 +690,7 @@ static u8 cs_etm__cpu_mode(struct cs_etm_queue *etmq, u64 address)
>  
>  	machine = etmq->etm->machine;
>  
> -	if (address >= etmq->etm->kernel_start) {
> +	if (address >= machine__kernel_start(machine)) {
>  		if (machine__is_host(machine))
>  			return PERF_RECORD_MISC_KERNEL;
>  		else
> @@ -901,9 +900,6 @@ static int cs_etm__setup_queues(struct cs_etm_auxtrace *etm)
>  	unsigned int i;
>  	int ret;
>  
> -	if (!etm->kernel_start)
> -		etm->kernel_start = machine__kernel_start(etm->machine);
> -
>  	for (i = 0; i < etm->queues.nr_queues; i++) {
>  		ret = cs_etm__setup_queue(etm, &etm->queues.queue_array[i], i);
>  		if (ret)
> -- 
> 2.28.0
>