linux-kernel - Re: [PATCH v2 03/14] perf arm-spe: Refactor payload length calculation

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Message-ID: <20201012002102.GB15194@leoy-ThinkPad-X240s>
Date:   Mon, 12 Oct 2020 08:21:02 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     André Przywara <andre.przywara@....com>
Cc:     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 03/14] perf arm-spe: Refactor payload length
 calculation

Hi Andre,

On Thu, Oct 08, 2020 at 02:44:59PM +0100, André Przywara wrote:
> On 29/09/2020 14:39, Leo Yan wrote:
> 
> Hi Leo,
> 
> > Defines macro for payload length calculation instead of static function.
> 
> What is the reason for that? I thought the kernel's direction is more
> the other way: replacing macros with static functions ("Don't write CPP,
> write C")? Ideally the compiler would generate the same code.

Okay, I didn't note this before.  Will change back to use static
function.

> > Currently the event packet's 'index' is assigned as payload length, but
> > the flow is not directive: it firstly gets the packet length (includes
> > header length and payload length) and then reduces header length from
> > packet length, so finally get the payload length; to simplify the code,
> > this patch directly assigns payload length to event packet's index.
> > 
> > Signed-off-by: Leo Yan <leo.yan@...aro.org>
> > ---
> >  .../arm-spe-decoder/arm-spe-pkt-decoder.c     | 26 ++++++++-----------
> >  .../arm-spe-decoder/arm-spe-pkt-decoder.h     |  4 +++
> >  2 files changed, 15 insertions(+), 15 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 7c7b5eb09fba..5a8696031e16 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
> > @@ -69,22 +69,20 @@ const char *arm_spe_pkt_name(enum arm_spe_pkt_type type)
> >  	return arm_spe_packet_name[type];
> >  }
> >  
> > -/* return ARM SPE payload size from its encoding,
> > - * which is in bits 5:4 of the byte.
> > - * 00 : byte
> > - * 01 : halfword (2)
> > - * 10 : word (4)
> > - * 11 : doubleword (8)
> > +/*
> > + * Return ARM SPE payload size from header bits 5:4
> > + *   00 : byte
> > + *   01 : halfword (2)
> > + *   10 : word (4)
> > + *   11 : doubleword (8)
> >   */
> > -static int payloadlen(unsigned char byte)
> > -{
> > -	return 1 << ((byte & 0x30) >> 4);
> > -}
> > +#define PAYLOAD_LEN(val)	\
> > +	(1 << (((val) & SPE_HEADER_SZ_MASK) >> SPE_HEADER_SZ_SHIFT))
> 
> This change of the expression is good (although it should be 1U), but
> please keep it a function. The return type should be unsigned, I guess.

Will do.

> The rest looks fine.

Thanks a lot for reviewing!

Leo

> Cheers,
> Andre
> 
> >  
> >  static int arm_spe_get_payload(const unsigned char *buf, size_t len,
> >  			       struct arm_spe_pkt *packet)
> >  {
> > -	size_t payload_len = payloadlen(buf[0]);
> > +	size_t payload_len = PAYLOAD_LEN(buf[0]);
> >  
> >  	if (len < 1 + payload_len)
> >  		return ARM_SPE_NEED_MORE_BYTES;
> > @@ -136,8 +134,6 @@ static int arm_spe_get_timestamp(const unsigned char *buf, size_t len,
> >  static int arm_spe_get_events(const unsigned char *buf, size_t len,
> >  			      struct arm_spe_pkt *packet)
> >  {
> > -	int ret = arm_spe_get_payload(buf, len, packet);
> > -
> >  	packet->type = ARM_SPE_EVENTS;
> >  
> >  	/* we use index to identify Events with a less number of
> > @@ -145,9 +141,9 @@ static int arm_spe_get_events(const unsigned char *buf, size_t len,
> >  	 * LLC-REFILL, and REMOTE-ACCESS events are identified if
> >  	 * index > 1.
> >  	 */
> > -	packet->index = ret - 1;
> > +	packet->index = PAYLOAD_LEN(buf[0]);
> >  
> > -	return ret;
> > +	return arm_spe_get_payload(buf, len, packet);
> >  }
> >  
> >  static int arm_spe_get_data_source(const unsigned char *buf, size_t len,
> > 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 4c870521b8eb..f2d0af39a58c 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
> > @@ -9,6 +9,7 @@
> >  
> >  #include <stddef.h>
> >  #include <stdint.h>
> > +#include <linux/bits.h>
> >  
> >  #define ARM_SPE_PKT_DESC_MAX		256
> >  
> > @@ -36,6 +37,9 @@ struct arm_spe_pkt {
> >  	uint64_t		payload;
> >  };
> >  
> > +#define SPE_HEADER_SZ_SHIFT		(4)
> > +#define SPE_HEADER_SZ_MASK		GENMASK_ULL(5, 4)
> > +
> >  #define SPE_ADDR_PKT_HDR_INDEX_INS		(0x0)
> >  #define SPE_ADDR_PKT_HDR_INDEX_BRANCH		(0x1)
> >  #define SPE_ADDR_PKT_HDR_INDEX_DATA_VIRT	(0x2)
> > 
>