Messages in this thread | | | Date | Wed, 30 Sep 2020 19:04:53 +0800 | From | Leo Yan <> | Subject | Re: [PATCH 5/5] perf: arm_spe: Decode SVE events |
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Hi Dave,
On Wed, Sep 30, 2020 at 11:34:11AM +0100, Dave Martin wrote:
[...]
> > > > >> 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 a033f34846a6..f0c369259554 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 > > > > >> @@ -372,8 +372,35 @@ int arm_spe_pkt_desc(const struct arm_spe_pkt *packet, char *buf, > > > > >> } > > > > >> case ARM_SPE_OP_TYPE: > > > > >> switch (idx) { > > > > >> - case 0: return snprintf(buf, buf_len, "%s", payload & 0x1 ? > > > > >> + case 0: { > > > > >> + size_t blen = buf_len; > > > > >> + > > > > >> + if ((payload & 0x89) == 0x08) { > > > > >> + ret = snprintf(buf, buf_len, "SVE"); > > > > >> + buf += ret; > > > > >> + blen -= ret; > > > > > > > > > > (Nit: can ret be < 0 ? I've never been 100% clear on this myself for > > > > > the s*printf() family -- if this assumption is widespread in perf tool > > > > > a lready that I guess just go with the flow.) > > > > > > > > Yeah, some parts of the code in here check for -1, actually, but doing > > > > this on every call to snprintf would push this current code over the > > > > edge - and I cowardly avoided a refactoring ;-) > > > > > > > > Please note that his is perf userland, and also we are printing constant > > > > strings here. > > > > Although admittedly this starts to sounds like an excuse now ... > > > > > > > > > I wonder if this snprintf+increment+decrement sequence could be wrapped > > > > > up as a helper, rather than having to be repeated all over the place. > > > > > > > > Yes, I was hoping nobody would notice ;-) > > > > > > It's probably not worth losing sleep over. > > > > > > snprintf(3) says, under NOTES: > > > > > > Until glibc 2.0.6, they would return -1 when the output was > > > truncated. > > > > > > which is probably ancient enough history that we don't care. C11 does > > > say that a negative return value can happen "if an encoding error > > > occurred". _Probably_ not a problem if perf tool never calls > > > setlocale(), but ... > > > > I have one patch which tried to fix the snprintf+increment sequence > > [1], to be honest, the change seems urgly for me. I agree it's better > > to use a helper to wrap up. > > > > [1] https://lore.kernel.org/patchwork/patch/1288410/ > > Sure, putting explicit checks all over the place makes a lot of noise in > the code. > > I was wondering whether something along the following lines would work: > > /* ... */ > > if (payload & SVE_EVT_PKT_GEN_EXCEPTION) > buf_appendf_err(&buf, &buf_len, &ret, " EXCEPTION-GEN"); > if (payload & SVE_EVT_PKT_ARCH_RETIRED) > buf_appendf_err(&buf, &buf_len, &ret, " RETIRED"); > if (payload & SVE_EVT_PKT_L1D_ACCESS) > buf_appendf_err(&buf, &buf_len, &ret, " L1D-ACCESS"); > > /* ... */ > > if (ret) > return ret; > > [...]
I have sent out the patch v2 [1] and Cc'ed you; I used a similiar API definition with your suggestion:
static int arm_spe_pkt_snprintf(char **buf_p, size_t *blen, const char *fmt, ...)
Only a difference is when return from arm_spe_pkt_snprintf(), will check the return value and directly bail out when detect failure. Your input will be considered for next spin.
> Best to keep such refactoring independent of this series though.
Yeah, the patch set [2] is quite heavy; after get some reviewing, maybe need to consider to split into 2 or even 3 small patch sets.
Thanks a lot for your suggestions!
Leo
[1] https://lore.kernel.org/patchwork/patch/1314603/ [2] https://lore.kernel.org/patchwork/cover/1314599/
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