Messages in this thread | | | Subject | Re: [PATCH v7 7/8] perf tools: Check write_backward during evlist config | From | "Wangnan (F)" <> | Date | Mon, 20 Jun 2016 12:09:44 +0800 |
| |
On 2016/6/17 5:47, Arnaldo Carvalho de Melo wrote: > Em Wed, Jun 15, 2016 at 02:23:34AM +0000, Wang Nan escreveu: >> Before this patch, when using overwritable ring buffer on an old >> kernel, error message is misleading: >> >> # ~/perf record -m 1 -e raw_syscalls:*/overwrite/ -a >> Error: >> The raw_syscalls:sys_enter event is not supported. >> >> This patch output clear error message to tell user his/her kernel >> is too old: >> >> # ~/perf record -m 1 -e raw_syscalls:*/overwrite/ -a >> Reading from overwrite event is not supported by this kernel >> Error: >> The raw_syscalls:sys_enter event is not supported. > So I went to see if exposing that missing_features struct outside > evsel.c was strictly needed and found that we already have fallbacking > for this feature (attr.write_backwards) i.e. if we set it and > sys_perf_event_open() fails, we will check if we are asking the kernel > for some attr. field that it doesn't supports, set that missing_features > and try again. > > But the way this was done for attr.write_backwards was buggy, as we need > to check features in the inverse order of their introduction to the > kernel, so that a newer tool checks first the newest perf_event_attr > fields, detecting that the older kernel doesn't have support for them. > The patch that introduced write_backwards support ([1]) in perf_evsel__open() > did this checking after all the other older attributes, wrongly. > > [1]: b90dc17a5d14 ("perf evsel: Add overwrite attribute and check write_backward") > > Also we shouldn't even try to call sys_perf_event_open if > perf_missing_features.write_backward is true and evsel->overwrite is > also true, the old code would check this only after successfully opening > the fd, do it before the open loop. > > Please take a look at the following patch, see if it is sufficient for > handling older kernels, probably we need to emit a message to the user, > but that has to be done at the builtin- level, i.e. at the tool, i.e. > perf_evsel_open__strerror() should have what it takes to figure out this > extra error and provide/ a proper string, lemme add this to the patch... > done, please check: > > write_backwards_fallback.patch:
[SNIP]
> > @@ -1496,7 +1493,10 @@ try_fallback: > * Must probe features in the order they were added to the > * perf_event_attr interface. > */
I read this comment but misunderstand. I thought 'order' means newest last.
Will try your patch. Thank you.
> - if (!perf_missing_features.clockid_wrong && evsel->attr.use_clockid) { > + if (!perf_missing_features.write_backward && evsel->attr.write_backward) { > + perf_missing_features.write_backward = true; > + goto fallback_missing_features; > + } else if (!perf_missing_features.clockid_wrong && evsel->attr.use_clockid) { > perf_missing_features.clockid_wrong = true; > goto fallback_missing_features; > } else if (!perf_missing_features.clockid && evsel->attr.use_clockid) { > @@ -1521,10 +1521,6 @@ try_fallback: > PERF_SAMPLE_BRANCH_NO_FLAGS))) { > perf_missing_features.lbr_flags = true; > goto fallback_missing_features; > - } else if (!perf_missing_features.write_backward && > - evsel->attr.write_backward) { > - perf_missing_features.write_backward = true; > - goto fallback_missing_features; > } > > out_close: > @@ -2409,6 +2405,8 @@ int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target, > "We found oprofile daemon running, please stop it and try again."); > break; > case EINVAL: > + if (evsel->overwrite && perf_missing_features.write_backward) > + return scnprintf(msg, size, "Reading from overwrite event is not supported by this kernel."); > if (perf_missing_features.clockid) > return scnprintf(msg, size, "clockid feature not supported."); > if (perf_missing_features.clockid_wrong)
| |