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Date: Fri, 15 Mar 2019 15:52:25 +0100 From: Jiri Olsa <jolsa@...hat.com> To: Arnaldo Carvalho de Melo <acme@...nel.org> Cc: Andi Kleen <ak@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Jonas Rabenstein <jonas.rabenstein@...dium.uni-erlangen.de>, Nageswara R Sastry <nasastry@...ibm.com>, Ravi Bangoria <ravi.bangoria@...ux.ibm.com> Subject: Re: [PATCH] perf tools: Move precise_ip detection into perf_evsel__open On Fri, Mar 15, 2019 at 11:35:04AM -0300, Arnaldo Carvalho de Melo wrote: SNIP > > +static void display_attr(struct perf_event_attr *attr) > > +{ > > + if (verbose >= 2) { > > + fprintf(stderr, "%.60s\n", graph_dotted_line); > > + fprintf(stderr, "perf_event_attr:\n"); > > + perf_event_attr__fprintf(stderr, attr, __open_attr__fprintf, NULL); > > + fprintf(stderr, "%.60s\n", graph_dotted_line); > > + } > > +} > > + > > +static int perf_event_open(struct perf_evsel *evsel, > > + pid_t pid, int cpu, int group_fd, > > + unsigned long flags) > > > The patch is ok, but I think the naming of this function is too generic, > so I'm renaming it to: > > static int perf_evsel__open_adjust_precise_ip(struct perf_evsel *evsel, > pid_t pid, int cpu, int group_fd, > unsigned long flags) > > Ok? ok > > The perf_evsel__open() code is already complex with that fallback > mechanism, this is just one more way of fallbacking when asking the > kernel for something that may fail. > > In fact what happens if the precise_ip that is being asked _is_ > supported but sys_perf_event_open() fails because some other > perf_event_attr attribute that is set is not supported? it's outside the scope of standard feature fallback code, so we will try it for any possible fallback variant, so: we will try all possible precise_ip (3,2,1,0) and they will all fail because of the unsupported attribute - so we will restore the precise_ip back and continue in standard fallback code that will eventualy switch that attribute off > > I see, it gets it back restored to what the user asked so that the > standard fallback is tried, ok, I'll apply with just the rename for this > function, thanks, jirka
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