Messages in this thread | | | Date | Wed, 30 Sep 2020 11:34:11 +0100 | From | Dave Martin <> | Subject | Re: [PATCH 5/5] perf: arm_spe: Decode SVE events |
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On Tue, Sep 29, 2020 at 10:19:02AM +0800, Leo Yan wrote: > On Mon, Sep 28, 2020 at 03:47:56PM +0100, Dave Martin wrote: > > On Mon, Sep 28, 2020 at 02:59:34PM +0100, André Przywara wrote: > > > On 28/09/2020 14:21, Dave Martin wrote: > > > > > > Hi Dave, > > > > > > > On Tue, Sep 22, 2020 at 11:12:25AM +0100, Andre Przywara wrote: > > > >> The Scalable Vector Extension (SVE) is an ARMv8 architecture extension > > > >> that introduces very long vector operations (up to 2048 bits). > > > > > > > > (8192, in fact, though don't expect to see that on real hardware any > > > > time soon... qemu and the Arm fast model can do it, though.) > > > > > > > >> The SPE profiling feature can tag SVE instructions with additional > > > >> properties like predication or the effective vector length. > > > >> > > > >> Decode the new operation type bits in the SPE decoder to allow the perf > > > >> tool to correctly report about SVE instructions. > > > > > > > > > > > > I don't know anything about SPE, so just commenting on a few minor > > > > things that catch my eye here. > > > > > > Many thanks for taking a look! > > > Please note that I actually missed a prior submission by Wei, so the > > > code changes here will end up in: > > > https://lore.kernel.org/patchwork/patch/1288413/ > > > > > > But your two points below magically apply to his patch as well, so.... > > > > > > > > > > >> Signed-off-by: Andre Przywara <andre.przywara@arm.com> > > > >> --- > > > >> .../arm-spe-decoder/arm-spe-pkt-decoder.c | 48 ++++++++++++++++++- > > > >> 1 file changed, 47 insertions(+), 1 deletion(-) > > > >> > > > >> 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;
[...]
Best to keep such refactoring independent of this series though.
Cheers ---Dave
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