发自我的 iPhone
> 在 2016年7月1日，下午9:40，Arnaldo Carvalho de Melo <a...@kernel.org> 写道：
>
> Em Fri, Jul 01, 2016 at 02:23:44AM +0000, Wang Nan escreveu:
>> From: Arnaldo Carvalho de Melo <a...@redhat.com>
>>
>> 'perf test backward' FAILED on old kernel:
>>
>> [root@jouet ~]# perf test -v backward
>> 45: Test backward reading from ring buffer :
>> --- start ---
>> <SNIP>
>> mmap size 1052672B
>> Unexpected counter: sample_count=0, comm_count=0
>> ---- end ----
>> Test backward reading from ring buffer: FAILED!
>> [root@jouet ~]#
>>
>> Reason: when kernel doesn't support 'attr.backward', perf_evsel__open() will
>> trim this bit and try again, unless evsel->overwrite is true.
>>
>> Set evsel->overwrite in this test.
>
> This fixes it, but then, if we get attr.backward set and the kernel
> doesn't support it, what whould be the point of trying without it? I.e.
> its not like we can do what is being asked for by fallbacking to some
> other method.
>
> I.e. perhaps evsel->overwrite is completely unnecessary and places
> checking for it should instead check for evsel->attr.backward, no?
>
If we remove evsel->overwrite, what should
we set in parser? Make it directly setting
attr?
Thank you.
> Something like the patch below, with it I also get:
>
> [root@jouet perf]# perf test backward
> 45: Test backward reading from ring buffer : Skip
> [root@jouet perf]# perf test -v backward 2>&1 | grep -v regist
> 45: Test backward reading from ring buffer :
> --- start ---
> test child forked, pid 29997
> perf_evlist__open: Invalid argument
> test child finished with -2
> ---- end ----
> Test backward reading from ring buffer: Skip
> [root@jouet perf]#
>
> - Arnaldo
>
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 113507716044..060c3b3d14db 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -1003,7 +1003,7 @@ static bool
> perf_evlist__should_poll(struct perf_evlist *evlist __maybe_unused,
> struct perf_evsel *evsel)
> {
> - if (evsel->overwrite)
> + if (evsel->attr.write_backward)
> return false;
> return true;
> }
> @@ -1018,7 +1018,7 @@ static int perf_evlist__mmap_per_evsel(struct
> perf_evlist *evlist, int idx,
> evlist__for_each_entry(evlist, evsel) {
> int fd;
>
> - if (evsel->overwrite != (evlist->overwrite && evlist->backward))
> + if (evsel->attr.write_backward != (evlist->overwrite &&
> evlist->backward))
> continue;
>
> if (evsel->system_wide && thread)
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 0fea724e735c..3abe5195fe80 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1359,6 +1359,9 @@ static int __perf_evsel__open(struct perf_evsel *evsel,
> struct cpu_map *cpus,
> int pid = -1, err;
> enum { NO_CHANGE, SET_TO_MAX, INCREASED_MAX } set_rlimit = NO_CHANGE;
>
> + if (perf_missing_features.write_backward && evsel->attr.write_backward)
> + return -EINVAL;
> +
> if (evsel->system_wide)
> nthreads = 1;
> else
> @@ -1389,11 +1392,6 @@ fallback_missing_features:
> if (perf_missing_features.lbr_flags)
> evsel->attr.branch_sample_type &= ~(PERF_SAMPLE_BRANCH_NO_FLAGS |
> PERF_SAMPLE_BRANCH_NO_CYCLES);
> - if (perf_missing_features.write_backward) {
> - if (evsel->overwrite)
> - return -EINVAL;
> - evsel->attr.write_backward = false;
> - }
> retry_sample_id:
> if (perf_missing_features.sample_id_all)
> evsel->attr.sample_id_all = 0;
> @@ -1495,7 +1493,7 @@ try_fallback:
> */
> if (!perf_missing_features.write_backward && evsel->attr.write_backward) {
> perf_missing_features.write_backward = true;
> - goto fallback_missing_features;
> + goto out_close;
> } else if (!perf_missing_features.clockid_wrong &&
> evsel->attr.use_clockid) {
> perf_missing_features.clockid_wrong = true;
> goto fallback_missing_features;
> @@ -2404,7 +2402,7 @@ 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)
> + if (evsel->attr.write_backward &&
> 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.");
> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> index 86fed7a2932b..a31ee2d5d2d3 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -114,7 +114,6 @@ struct perf_evsel {
> bool tracking;
> bool per_pkg;
> bool precise_max;
> - bool overwrite;
> /* parse modifier helper */
> int exclude_GH;
> int nr_members;
