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Date: Thu, 30 Aug 2012 12:29:25 -0600
From: David Ahern <dsahern@gmail.com>
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To: Dong Hao <haodong@linux.vnet.ibm.com>
CC: avi@redhat.com, acme@infradead.org, mtosatti@redhat.com, mingo@elte.hu,
        xiaoguangrong@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Subject: Re: [PATCH v7 3/3] KVM: perf: kvm events analysis tool
References: <1346061106-5364-1-git-send-email-haodong@linux.vnet.ibm.com> <1346061106-5364-4-git-send-email-haodong@linux.vnet.ibm.com>
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In addition to Andrew's comment about making the stats struct and 
functions generic...

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.

---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.

---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?

---8<---

> +/* returns left most element of result, and erase it */
> +static struct kvm_event *pop_from_result(void)
> +{
> +	struct rb_node *node = result.rb_node;
> +
> +	if (!node)
> +		return NULL;
> +
> +	while (node->rb_left)
> +		node = node->rb_left;

Use rb_first().

---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.

---8<---

> +static const char * const kvm_events_report_usage[] = {
> +	"perf kvm stat report [<options>]",
> +	NULL
> +};
> +
> +static const struct option kvm_events_report_options[] = {
> +	OPT_STRING(0, "event", &report_event, "report event",
> +		    "event for reporting: vmexit, mmio, ioport"),
> +	OPT_INTEGER(0, "vcpu", &trace_vcpu,
> +		    "vcpu id to report"),
> +	OPT_STRING('k', "key", &sort_key, "sort-key",
> +		    "key for sorting: sample(sort by samples number)"
> +		    " time (sort by avg time)"),
> +	OPT_END()
> +};
> +
> +static int kvm_events_report(int argc, const char **argv)
> +{
> +	symbol__init();
> +
> +	if (argc) {
> +		argc = parse_options(argc, argv,
> +				     kvm_events_report_options,
> +				     kvm_events_report_usage, 0);
> +		if (argc)
> +			usage_with_options(kvm_events_report_usage,
> +					   kvm_events_report_options);
> +	}
> +
> +	return kvm_events_report_vcpu(trace_vcpu);
> +}
> +
> +static int kvm_cmd_stat(int argc, const char **argv)
> +{
> +	if (argc > 1) {
> +		if (!strncmp(argv[1], "rec", 3))
> +			return kvm_events_record(argc - 1, argv + 1);
> +
> +		if (!strncmp(argv[1], "rep", 3))
> +			return kvm_events_report(argc - 1 , argv + 1);
> +	}
> +
> +	return cmd_stat(argc, argv, NULL);
> +}
> +
>   static char			name_buffer[256];
>
>   static const char * const kvm_usage[] = {
> -	"perf kvm [<options>] {top|record|report|diff|buildid-list}",
> +	"perf kvm [<options>] {top|record|report|diff|buildid-list|stat}",
>   	NULL
>   };
>

The usage for the report/record sub commands of stat is never shown. e.g.,
$ perf kvm stat
--> shows help for perf-stat

$ perf kvm
--> shows the above and perf-kvm's usage

To get help for the record/report subcommands you have to know that 
record and report are subcommands.

---8<---

> +static int perf_file_section__read_feature(struct perf_file_section *section,
> +				struct perf_header *ph,
> +				int feat, int fd, void *data)
> +{
> +	struct header_read_data *hd = data;
> +
> +	if (feat != hd->feat)
> +		return 0;
> +
> +	if (lseek(fd, section->offset, SEEK_SET) == (off_t)-1) {
> +		pr_debug("Failed to lseek to %" PRIu64 " offset for feature "
> +				"%d, continuing...\n", section->offset, feat);
> +	return 0;
> +	}
> +
> +	if (feat >= HEADER_LAST_FEATURE) {
> +		pr_warning("unknown feature %d\n", feat);
> +		return 0;
> +	}
> +
> +	hd->result = feat_ops[feat].read(ph, fd);

you should verify the read() function is implemented for the requested 
feature.

David
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