linux-kernel - Re: [PATCH v2 09/14] perf arm-spe: Refactor counter packet handling

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Message-ID: <6080472e-a117-e36d-ec4a-80f7ef93b3fb@arm.com>
Date:   Tue, 20 Oct 2020 22:53:47 +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>,
        Dave Martin <Dave.Martin@....com>,
        linux-kernel@...r.kernel.org, Al Grant <Al.Grant@....com>
Subject: Re: [PATCH v2 09/14] perf arm-spe: Refactor counter packet handling

On 29/09/2020 14:39, Leo Yan wrote:

Hi,

> This patch defines macros for counter packet header, and uses macro to
> replace hard code values for packet parsing.
> 
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> ---
>  .../util/arm-spe-decoder/arm-spe-pkt-decoder.c  | 17 ++++++++++-------
>  .../util/arm-spe-decoder/arm-spe-pkt-decoder.h  |  9 +++++++++
>  2 files changed, 19 insertions(+), 7 deletions(-)
> 
> 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 00a2cd1af422..ed0f4c74dfc5 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
> @@ -150,10 +150,13 @@ static int arm_spe_get_counter(const unsigned char *buf, size_t len,
>  			       const unsigned char ext_hdr, struct arm_spe_pkt *packet)
>  {
>  	packet->type = ARM_SPE_COUNTER;
> -	if (ext_hdr)
> -		packet->index = ((buf[0] & 0x3) << 3) | (buf[1] & 0x7);
> -	else
> -		packet->index = buf[0] & 0x7;
> +	if (ext_hdr) {
> +		packet->index  = (buf[1] & SPE_CNT_PKT_HDR_INDEX_MASK);
> +		packet->index |= ((buf[0] & SPE_CNT_PKT_HDR_EXT_INDEX_MASK)
> +			<< SPE_CNT_PKT_HDR_EXT_INDEX_SHIFT);
> +	} else {
> +		packet->index = buf[0] & SPE_CNT_PKT_HDR_INDEX_MASK;

That looks suspiciously similar to the extended header in the address
packet. Can you use the same name for that?
And, similar to the address packet, what about:
	packet->index |= SPE_PKT_EXT_HEADER_INDEX(buf[0]);

(merging the mask and the shift in the macro definition)

> +	}
>  
>  	return arm_spe_get_payload(buf, len, ext_hdr, packet);
>  }
> @@ -431,17 +434,17 @@ int arm_spe_pkt_desc(const struct arm_spe_pkt *packet, char *buf,
>  			return ret;
>  
>  		switch (idx) {
> -		case 0:
> +		case SPE_CNT_PKT_HDR_INDEX_TOTAL_LAT:
>  			ret = arm_spe_pkt_snprintf(&buf, &blen, "TOT");
>  			if (ret < 0)
>  				return ret;
>  			break;
> -		case 1:
> +		case SPE_CNT_PKT_HDR_INDEX_ISSUE_LAT:
>  			ret = arm_spe_pkt_snprintf(&buf, &blen, "ISSUE");
>  			if (ret < 0)
>  				return ret;
>  			break;
> -		case 2:
> +		case SPE_CNT_PKT_HDR_INDEX_TRANS_LAT:
>  			ret = arm_spe_pkt_snprintf(&buf, &blen, "XLAT");
>  			if (ret < 0)
>  				return ret;
> diff --git a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.h b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.h
> index 62db4ff91832..18667a63f5ba 100644
> --- a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.h
> +++ b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.h
> @@ -89,6 +89,15 @@ struct arm_spe_pkt {
>  /* Context packet header */
>  #define SPE_CTX_PKT_HDR_INDEX_MASK		GENMASK_ULL(1, 0)
>  
> +/* Counter packet header */
> +#define SPE_CNT_PKT_HDR_INDEX_MASK		GENMASK_ULL(2, 0)
> +#define SPE_CNT_PKT_HDR_INDEX_TOTAL_LAT		(0x0)
> +#define SPE_CNT_PKT_HDR_INDEX_ISSUE_LAT		(0x1)
> +#define SPE_CNT_PKT_HDR_INDEX_TRANS_LAT		(0x2)

I think the Linux kernel coding style does not mention parentheses just
around numbers, so just 0x2 would suffice, for instance.
See section 12) in Documentation/process/coding-style.rst

Cheers,
Andre


> +
> +#define SPE_CNT_PKT_HDR_EXT_INDEX_MASK		GENMASK_ULL(1, 0)
> +#define SPE_CNT_PKT_HDR_EXT_INDEX_SHIFT		(3)
> +
>  const char *arm_spe_pkt_name(enum arm_spe_pkt_type);
>  
>  int arm_spe_get_packet(const unsigned char *buf, size_t len,
>