linux-kernel - Re: [PATCH v6 06/21] perf arm-spe: Refactor printing string to buffer

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Message-ID: <20201106015828.GA13572@leoy-ThinkPad-X240s>
Date:   Fri, 6 Nov 2020 09:58:28 +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>,
        James Clark <james.clark@....com>,
        Dave Martin <Dave.Martin@....com>, Al Grant <Al.Grant@....com>,
        Wei Li <liwei391@...wei.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 06/21] perf arm-spe: Refactor printing string to buffer

Hi Andre, Dave,

On Mon, Nov 02, 2020 at 03:50:01PM +0000, André Przywara wrote:

[...]

> >  int arm_spe_pkt_desc(const struct arm_spe_pkt *packet, char *buf,
> >  		     size_t buf_len)
> >  {
> > -	int ret, ns, el, idx = packet->index;
> > +	int ns, el, idx = packet->index;
> >  	unsigned long long payload = packet->payload;
> >  	const char *name = arm_spe_pkt_name(packet->type);
> > +	size_t blen = buf_len;
> > +	int err = 0;
> >  
> >  	switch (packet->type) {
> >  	case ARM_SPE_BAD:
> >  	case ARM_SPE_PAD:
> >  	case ARM_SPE_END:
> > -		return snprintf(buf, buf_len, "%s", name);
> > -	case ARM_SPE_EVENTS: {
> > -		size_t blen = buf_len;
> > -
> > -		ret = 0;
> > -		ret = snprintf(buf, buf_len, "EV");
> > -		buf += ret;
> > -		blen -= ret;
> > -		if (payload & 0x1) {
> > -			ret = snprintf(buf, buf_len, " EXCEPTION-GEN");
> > -			buf += ret;
> > -			blen -= ret;
> > -		}
> > -		if (payload & 0x2) {
> > -			ret = snprintf(buf, buf_len, " RETIRED");
> > -			buf += ret;
> > -			blen -= ret;
> > -		}
> > -		if (payload & 0x4) {
> > -			ret = snprintf(buf, buf_len, " L1D-ACCESS");
> > -			buf += ret;
> > -			blen -= ret;
> > -		}
> > -		if (payload & 0x8) {
> > -			ret = snprintf(buf, buf_len, " L1D-REFILL");
> > -			buf += ret;
> > -			blen -= ret;
> > -		}
> > -		if (payload & 0x10) {
> > -			ret = snprintf(buf, buf_len, " TLB-ACCESS");
> > -			buf += ret;
> > -			blen -= ret;
> > -		}
> > -		if (payload & 0x20) {
> > -			ret = snprintf(buf, buf_len, " TLB-REFILL");
> > -			buf += ret;
> > -			blen -= ret;
> > -		}
> > -		if (payload & 0x40) {
> > -			ret = snprintf(buf, buf_len, " NOT-TAKEN");
> > -			buf += ret;
> > -			blen -= ret;
> > -		}
> > -		if (payload & 0x80) {
> > -			ret = snprintf(buf, buf_len, " MISPRED");
> > -			buf += ret;
> > -			blen -= ret;
> > -		}
> > +		return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s", name);
> 
> Nothing critical, but in case you need to respin this series for
> whatever reason, you might want to use NULL for the first argument,
> since you return here and there is little point in setting err. Same for
> other cases where you return directly from an arm_spe_pkt_snprintf() call.
> But it doesn't hurt, so you could leave it as well, and it's more robust
> in case someone extends the code later.

Just remind, in the new patch set v7, I don't change to use NULL for
the first argument and still pass '&err', the main reason is to
consolidate with return value, which is heavily dependent on the 'err'
parameter of arm_spe_pkt_snprintf(); the brief form is as follow:

    switch (type) {
    ...
    case ARM_SPE_END:
        arm_spe_pkt_snprintf(&err, &buf, &blen, "%s", name);
        break;
    ...
    default:
        break;
    }

    handle the 'err';

    return err;

Please see the new introduced patch [1] so it can give more idea for
the changes.

Thanks,
Leo

[1] https://lore.kernel.org/patchwork/patch/1333881/