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Date: Tue, 3 Nov 2020 10:39:36 +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
On Mon, Nov 02, 2020 at 03:50:01PM +0000, André Przywara wrote:
> On 30/10/2020 02:57, Leo Yan wrote:
> > When outputs strings to the decoding buffer with function snprintf(),
> > SPE decoder needs to detects if any error returns from snprintf() and if
> > so needs to directly bail out. If snprintf() returns success, it needs
> > to update buffer pointer and reduce the buffer length so can continue to
> > output the next string into the consequent memory space.
> >
> > This complex logics are spreading in the function arm_spe_pkt_desc() so
> > there has many duplicate codes for handling error detecting, increment
> > buffer pointer and decrement buffer size.
> >
> > To avoid the duplicate code, this patch introduces a new helper function
> > arm_spe_pkt_snprintf() which is used to wrap up the complex logics, and
> > it's used by the caller arm_spe_pkt_desc(); if printing buffer is called
> > for multiple times in a flow, the error is a cumulative value and simply
> > returns its final value.
> >
> > This patch also moves the variable 'blen' as the function's local
> > variable, this allows to remove the unnecessary braces and improve the
> > readability.
> >
> > Suggested-by: Dave Martin <Dave.Martin@....com>
> > Signed-off-by: Leo Yan <leo.yan@...aro.org>
>
> Wow, that's a bit tricky to review in its current incarnation, but it
> looks alright to me.
Yes, I had the same feeling when I saw the generated patch :)
> I have some optimisation idea below, but that's a nit and the patch as
> is seems correct to me (checked twice, the second time in an editor,
> matching the lines), so:
>
> Reviewed-by: Andre Przywara <andre.przywara@....com>
>
>
> ...
>
> > ---
> > .../arm-spe-decoder/arm-spe-pkt-decoder.c | 267 ++++++++----------
> > 1 file changed, 117 insertions(+), 150 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 04fd7fd7c15f..1ecaf9805b79 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
> > @@ -9,6 +9,7 @@
> > #include <endian.h>
> > #include <byteswap.h>
> > #include <linux/bitops.h>
> > +#include <stdarg.h>
> >
> > #include "arm-spe-pkt-decoder.h"
> >
> > @@ -258,192 +259,158 @@ int arm_spe_get_packet(const unsigned char *buf, size_t len,
> > return ret;
> > }
> >
> > +static int arm_spe_pkt_snprintf(int *err, char **buf_p, size_t *blen,
> > + const char *fmt, ...)
> > +{
> > + va_list ap;
> > + int ret;
> > +
> > + /* Bail out if any error occurred */
> > + if (err && *err)
> > + return *err;
> > +
> > + va_start(ap, fmt);
> > + ret = vsnprintf(*buf_p, *blen, fmt, ap);
> > + va_end(ap);
> > +
> > + if (ret < 0) {
> > + if (err && !*err)
> > + *err = ret;
> > + } else {
> > + *buf_p += ret;
> > + *blen -= ret;
> > + }
> > +
> > + return ret;
> > +}
> > +
> > 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.
Makes sense for me. Eventually, we also can remove the local variable
"err", so will do it. Thanks a lot!
> > + case ARM_SPE_EVENTS:
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, "EV");
> > +
> > + if (payload & 0x1)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " EXCEPTION-GEN");
> > + if (payload & 0x2)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " RETIRED");
> > + if (payload & 0x4)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " L1D-ACCESS");
> > + if (payload & 0x8)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " L1D-REFILL");
> > + if (payload & 0x10)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " TLB-ACCESS");
> > + if (payload & 0x20)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " TLB-REFILL");
> > + if (payload & 0x40)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " NOT-TAKEN");
> > + if (payload & 0x80)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " MISPRED");
> > if (idx > 1) {
> > - if (payload & 0x100) {
> > - ret = snprintf(buf, buf_len, " LLC-ACCESS");
> > - buf += ret;
> > - blen -= ret;
> > - }
> > - if (payload & 0x200) {
> > - ret = snprintf(buf, buf_len, " LLC-REFILL");
> > - buf += ret;
> > - blen -= ret;
> > - }
> > - if (payload & 0x400) {
> > - ret = snprintf(buf, buf_len, " REMOTE-ACCESS");
> > - buf += ret;
> > - blen -= ret;
> > - }
> > + if (payload & 0x100)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " LLC-ACCESS");
> > + if (payload & 0x200)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " LLC-REFILL");
> > + if (payload & 0x400)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " REMOTE-ACCESS");
> > }
> > - if (ret < 0)
> > - return ret;
> > - blen -= ret;
> > - return buf_len - blen;
> > - }
> > + return err ?: (int)(buf_len - blen);
> > +
> > case ARM_SPE_OP_TYPE:
> > switch (idx) {
> > - case 0: return snprintf(buf, buf_len, "%s", payload & 0x1 ?
> > - "COND-SELECT" : "INSN-OTHER");
> > - case 1: {
> > - size_t blen = buf_len;
> > + case 0:
> > + return arm_spe_pkt_snprintf(&err, &buf, &blen,
> > + payload & 0x1 ? "COND-SELECT" : "INSN-OTHER");
>
> same here (and below, you get the idea ...)
>
> Cheers,
> Andre
>
>
> > + case 1:
> > + arm_spe_pkt_snprintf(&err, &buf, &blen,
> > + payload & 0x1 ? "ST" : "LD");
> >
> > - if (payload & 0x1)
> > - ret = snprintf(buf, buf_len, "ST");
> > - else
> > - ret = snprintf(buf, buf_len, "LD");
> > - buf += ret;
> > - blen -= ret;
> > if (payload & 0x2) {
> > - if (payload & 0x4) {
> > - ret = snprintf(buf, buf_len, " AT");
> > - buf += ret;
> > - blen -= ret;
> > - }
> > - if (payload & 0x8) {
> > - ret = snprintf(buf, buf_len, " EXCL");
> > - buf += ret;
> > - blen -= ret;
> > - }
> > - if (payload & 0x10) {
> > - ret = snprintf(buf, buf_len, " AR");
> > - buf += ret;
> > - blen -= ret;
> > - }
> > + if (payload & 0x4)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " AT");
> > + if (payload & 0x8)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " EXCL");
> > + if (payload & 0x10)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " AR");
> > } else if (payload & 0x4) {
> > - ret = snprintf(buf, buf_len, " SIMD-FP");
> > - buf += ret;
> > - blen -= ret;
> > - }
> > - if (ret < 0)
> > - return ret;
> > - blen -= ret;
> > - return buf_len - blen;
> > - }
> > - case 2: {
> > - size_t blen = buf_len;
> > -
> > - ret = snprintf(buf, buf_len, "B");
> > - buf += ret;
> > - blen -= ret;
> > - if (payload & 0x1) {
> > - ret = snprintf(buf, buf_len, " COND");
> > - buf += ret;
> > - blen -= ret;
> > - }
> > - if (payload & 0x2) {
> > - ret = snprintf(buf, buf_len, " IND");
> > - buf += ret;
> > - blen -= ret;
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " SIMD-FP");
> > }
> > - if (ret < 0)
> > - return ret;
> > - blen -= ret;
> > - return buf_len - blen;
> > - }
> > - default: return 0;
> > +
> > + return err ?: (int)(buf_len - blen);
> > +
> > + case 2:
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, "B");
> > +
> > + if (payload & 0x1)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " COND");
> > + if (payload & 0x2)
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, " IND");
> > +
> > + return err ?: (int)(buf_len - blen);
> > +
> > + default:
> > + return 0;
> > }
> > case ARM_SPE_DATA_SOURCE:
> > case ARM_SPE_TIMESTAMP:
> > - return snprintf(buf, buf_len, "%s %lld", name, payload);
> > + return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s %lld", name, payload);
> > case ARM_SPE_ADDRESS:
> > switch (idx) {
> > case 0:
> > case 1: ns = !!(packet->payload & NS_FLAG);
> > el = (packet->payload & EL_FLAG) >> 61;
> > payload &= ~(0xffULL << 56);
> > - return snprintf(buf, buf_len, "%s 0x%llx el%d ns=%d",
> > + return arm_spe_pkt_snprintf(&err, &buf, &blen,
> > + "%s 0x%llx el%d ns=%d",
> > (idx == 1) ? "TGT" : "PC", payload, el, ns);
> > - case 2: return snprintf(buf, buf_len, "VA 0x%llx", payload);
> > + case 2:
> > + return arm_spe_pkt_snprintf(&err, &buf, &blen,
> > + "VA 0x%llx", payload);
> > case 3: ns = !!(packet->payload & NS_FLAG);
> > payload &= ~(0xffULL << 56);
> > - return snprintf(buf, buf_len, "PA 0x%llx ns=%d",
> > - payload, ns);
> > - default: return 0;
> > + return arm_spe_pkt_snprintf(&err, &buf, &blen,
> > + "PA 0x%llx ns=%d", payload, ns);
> > + default:
> > + return 0;
> > }
> > case ARM_SPE_CONTEXT:
> > - return snprintf(buf, buf_len, "%s 0x%lx el%d", name,
> > - (unsigned long)payload, idx + 1);
> > - case ARM_SPE_COUNTER: {
> > - size_t blen = buf_len;
> > -
> > - ret = snprintf(buf, buf_len, "%s %d ", name,
> > - (unsigned short)payload);
> > - buf += ret;
> > - blen -= ret;
> > + return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s 0x%lx el%d",
> > + name, (unsigned long)payload, idx + 1);
> > + case ARM_SPE_COUNTER:
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, "%s %d ", name,
> > + (unsigned short)payload);
> > +
> > switch (idx) {
> > - case 0: ret = snprintf(buf, buf_len, "TOT"); break;
> > - case 1: ret = snprintf(buf, buf_len, "ISSUE"); break;
> > - case 2: ret = snprintf(buf, buf_len, "XLAT"); break;
> > - default: ret = 0;
> > + case 0:
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, "TOT");
> > + break;
> > + case 1:
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, "ISSUE");
> > + break;
> > + case 2:
> > + arm_spe_pkt_snprintf(&err, &buf, &blen, "XLAT");
> > + break;
> > + default:
> > + break;
> > }
> > - if (ret < 0)
> > - return ret;
> > - blen -= ret;
> > - return buf_len - blen;
> > - }
> > +
> > + return err ?: (int)(buf_len - blen);
> > +
> > default:
> > break;
> > }
> >
> > - return snprintf(buf, buf_len, "%s 0x%llx (%d)",
> > - name, payload, packet->index);
> > + return arm_spe_pkt_snprintf(&err, &buf, &blen, "%s 0x%llx (%d)",
> > + name, payload, packet->index);
> > }
> >
>
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