linux-kernel - Re: [PATCH v3 15/20] perf arm-spe: Remove size condition checking for events

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Message-ID: <d87b2f3b-e6f6-99aa-5a94-3ff348e8aaf4@arm.com>
Date:   Fri, 23 Oct 2020 18:10:39 +0100
From:   André Przywara <andre.przywara@....com>
To:     Leo Yan <leo.yan@...aro.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Wei Li <liwei391@...wei.com>,
        James Clark <james.clark@....com>, Al Grant <Al.Grant@....com>,
        Dave Martin <Dave.Martin@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 15/20] perf arm-spe: Remove size condition checking for
 events

On 22/10/2020 15:58, Leo Yan wrote:
> In the Armv8 ARM (ARM DDI 0487F.c), chapter "D10.2.6 Events packet", it
> describes the event bit is valid with specific payload requirement.  For
> example, the Last Level cache access event, the bit is defined as:
> 
>   E[8], byte 1 bit [0], when SZ == 0b01 , when SZ == 0b10 ,
>   		     or when SZ == 0b11
> 
> It requires the payload size is at least 2 bytes, when byte 1 (start
> counting from 0) is valid, E[8] (bit 0 in byte 1) can be used for LLC
> access event type.  For safety, the code checks the condition for
> payload size firstly, if meet the requirement for payload size, then
> continue to parse event type.
> 
> If review function arm_spe_get_payload(), it has used cast, so any bytes
> beyond the valid size have been set to zeros.
> 
> For this reason, we don't need to check payload size anymore afterwards
> when parse events, thus this patch removes payload size conditions.
> 
> Suggested-by: Andre Przywara <andre.przywara@....com>
> Signed-off-by: Leo Yan <leo.yan@...aro.org>

Thanks, that looks better now!

Reviewed-by: Andre Przywara <andre.przywara@....com>

Cheers,
Andre

> ---
>  .../util/arm-spe-decoder/arm-spe-decoder.c    |  9 ++----
>  .../arm-spe-decoder/arm-spe-pkt-decoder.c     | 30 +++++++++----------
>  2 files changed, 17 insertions(+), 22 deletions(-)
> 
> diff --git a/tools/perf/util/arm-spe-decoder/arm-spe-decoder.c b/tools/perf/util/arm-spe-decoder/arm-spe-decoder.c
> index 776b3e6628bb..a5d7509d5daa 100644
> --- a/tools/perf/util/arm-spe-decoder/arm-spe-decoder.c
> +++ b/tools/perf/util/arm-spe-decoder/arm-spe-decoder.c
> @@ -178,16 +178,13 @@ static int arm_spe_read_record(struct arm_spe_decoder *decoder)
>  			if (payload & BIT(EV_TLB_ACCESS))
>  				decoder->record.type |= ARM_SPE_TLB_ACCESS;
>  
> -			if ((idx == 2 || idx == 4 || idx == 8) &&
> -			    (payload & BIT(EV_LLC_MISS)))
> +			if (payload & BIT(EV_LLC_MISS))
>  				decoder->record.type |= ARM_SPE_LLC_MISS;
>  
> -			if ((idx == 2 || idx == 4 || idx == 8) &&
> -			    (payload & BIT(EV_LLC_ACCESS)))
> +			if (payload & BIT(EV_LLC_ACCESS))
>  				decoder->record.type |= ARM_SPE_LLC_ACCESS;
>  
> -			if ((idx == 2 || idx == 4 || idx == 8) &&
> -			    (payload & BIT(EV_REMOTE_ACCESS)))
> +			if (payload & BIT(EV_REMOTE_ACCESS))
>  				decoder->record.type |= ARM_SPE_REMOTE_ACCESS;
>  
>  			if (payload & BIT(EV_MISPRED))
> diff --git a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c
> index 58a1390b7a43..2cb019999016 100644
> --- a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c
> +++ b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c
> @@ -317,22 +317,20 @@ static int arm_spe_pkt_desc_event(const struct arm_spe_pkt *packet,
>  		if (ret < 0)
>  			return ret;
>  	}
> -	if (packet->index > 1) {
> -		if (payload & BIT(EV_LLC_ACCESS)) {
> -			ret = arm_spe_pkt_snprintf(&buf, &blen, " LLC-ACCESS");
> -			if (ret < 0)
> -				return ret;
> -		}
> -		if (payload & BIT(EV_LLC_MISS)) {
> -			ret = arm_spe_pkt_snprintf(&buf, &blen, " LLC-REFILL");
> -			if (ret < 0)
> -				return ret;
> -		}
> -		if (payload & BIT(EV_REMOTE_ACCESS)) {
> -			ret = arm_spe_pkt_snprintf(&buf, &blen, " REMOTE-ACCESS");
> -			if (ret < 0)
> -				return ret;
> -		}
> +	if (payload & BIT(EV_LLC_ACCESS)) {
> +		ret = arm_spe_pkt_snprintf(&buf, &blen, " LLC-ACCESS");
> +		if (ret < 0)
> +			return ret;
> +	}
> +	if (payload & BIT(EV_LLC_MISS)) {
> +		ret = arm_spe_pkt_snprintf(&buf, &blen, " LLC-REFILL");
> +		if (ret < 0)
> +			return ret;
> +	}
> +	if (payload & BIT(EV_REMOTE_ACCESS)) {
> +		ret = arm_spe_pkt_snprintf(&buf, &blen, " REMOTE-ACCESS");
> +		if (ret < 0)
> +			return ret;
>  	}
>  
>  	return buf_len - blen;
>