Messages in this thread | | | Date | Mon, 03 Sep 2012 10:04:37 -0600 | From | David Ahern <> | Subject | Re: [PATCH v7 3/3] KVM: perf: kvm events analysis tool |
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On 9/3/12 2:48 AM, don wrote: > 于 2012年08月31日 02:29, David Ahern 写道: >> In addition to Andrew's comment about making the stats struct and >> functions generic... > Yes. :-) >> >> On 8/27/12 3:51 AM, Dong Hao wrote: >> ---8<--- >> >>> +static void exit_event_decode_key(struct event_key *key, char >>> decode[20]) >>> +{ >>> + const char *exit_reason = get_exit_reason(key->key); >>> + >>> + snprintf(decode, 20, "%s", exit_reason); >>> +} >> >> Use scnprintf rather than snprintf. > Why? Since we don't care about the return value, what's the difference?
1. consistency (scnprintf is preferred). 2. what if a new exit reason is added in the future that is larger than 19 characters? Better to be safe now.
>> >> ---8<--- >> >>> +static bool kvm_event_expand(struct kvm_event *event, int vcpu_id) >>> +{ >>> + int old_max_vcpu = event->max_vcpu; >>> + >>> + if (vcpu_id < event->max_vcpu) >>> + return true; >>> + >>> + while (event->max_vcpu <= vcpu_id) >>> + event->max_vcpu += DEFAULT_VCPU_NUM; >>> + >>> + event->vcpu = realloc(event->vcpu, >>> + event->max_vcpu * sizeof(*event->vcpu)); >>> + if (!event->vcpu) { >> >> If realloc fails you leak memory by overwriting the current pointer. > Thanks for pointing it out, we will terminate the running instance in > our next > version.
Ok. Make sure to free the memory of the previous pointer on failure before cleaning up. The idea is that all allocations are properly freed on exit.
>> >> ---8<--- >> >>> +static double event_stats_stddev(int vcpu_id, struct kvm_event *event) >>> +{ >>> + struct event_stats *stats = &event->total; >>> + double variance, variance_mean, stddev; >>> + >>> + if (vcpu_id != -1) >>> + stats = &event->vcpu[vcpu_id]; >>> + >>> + BUG_ON(!stats->count); >>> + >>> + variance = stats->M2 / (stats->count - 1); >>> + variance_mean = variance / stats->count; >>> + stddev = sqrt(variance_mean); >>> + >>> + return stddev * 100 / stats->mean; >>> +} >> >> perf should be consistent in the stddev it shows the user. Any reason >> to dump relative stddev versus stddev used by perf-stat? > Since 'perf stat' uses relative standard deviation rather than stddev, > 'perf kvm stat' > just follows the style of 'perf stat'.
Yes, I've been working on an idea motivated by Andi Kleen. I have noticed that perf stat also uses relative stddev just in a non-direct way. I suggest moving common stats code from perf-stat to utils/stat.[ch], add a rel_stddev_stats function that returns the above and have perf-kvm use that.
>> ---8<--- >> >>> + /* >>> + * Append "-a" only if "-p"/"--pid" is not specified since they >>> + * are mutually exclusive. >>> + */ >>> + if (!kvm_record_specified_guest(argc, argv)) >>> + rec_argv[i++] = STRDUP_FAIL_EXIT("-a"); >> >> Other perf-kvm commands rely on perf-record semantics -- i.e., for >> user to add the -a or -p option. > You mean, remove '-a' from the default options, then: > if a user wants to record all guest he will use 'perf stat record -a'; > and if a user wants to record the specified guest, he should use > 'perf stat record -p xxx'?
Yes. Well, 'perf kvm stat record' with a -a or -p. That makes the new stat subcommand consistent with just 'perf kvm record'.
> > Well, as the style of other subcommand, e.g., perf lock/perf sched, the > 'perf xxx record' record all events on all cpus, no need to use '-a'. > > Based on mentioned above, I prefer the original way. ;)
Yes, I noticed that some commands add -a before calling cmd_record(). Can't change that but we can keep perf-kvm consistent with its own variants which means not automagically adding -a.
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