hwpmc: add summary command and further metadata extensions

metadata changes:
- log pmc sample rate with pmcallocate
- log proc flags with thread / process logging
  to identify user vs kernel threads

fixes:
- use log cpuid to translate event id to event name

Implement rudimentary summary command to track sample
counts by thread and process name within a pmc log.

% make -j4 buildkernel >& /dev/null &
% sudo pmcstat -S unhalted_core_cycles -S llc-misses -O foo sleep 15
% pmc summary foo
cpu_clk_unhalted.thread_p_any:
        idle: 138108207162
        clang-6.0: 105336158004
        sh: 72340108510
        make: 8642012963
        kernel: 7754011631
longest_lat_cache.miss:
        clang-6.0: 87502625
        sh: 40901227
        make: 5500165
        kernel: 3300099
        awk: 2000060

%  pmc summary -f ~/foo
idx: 278 name: cpu_clk_unhalted.thread_p_any rate: 2000003
idle: 69054
clang-6.0: 52668
sh: 36170
make: 4321
kernel: 3877
hwpmc: proc(7445): 3319
awk: 1289
xargs: 357
rand_harvestq: 181
mtree: 102
intr: 53
zfskern: 31
usb: 7
pagedaemon: 4
ntpd: 3
syslogd: 1
acpi_thermal: 1
logger: 1
syncer: 1
snmptrapd: 1
sleep: 1
idx: 17 name: longest_lat_cache.miss rate: 100003
clang-6.0: 875
sh: 409
make: 55
kernel: 33
awk: 20
hwpmc: proc(7445): 14
xargs: 9
idle: 8
intr: 3
zfskern: 2

share/examples/hwpmc/overhead.c

@@ -65,7 +65,7 @@ main(int argc, char **argv)
 	if (pmc_init() != 0)
 		err(EX_OSERR, "hwpmc(4) not loaded, kldload or update your kernel");
 
-	if (pmc_allocate(counter_name, PMC_MODE_SC, 0, 0, &pmcid) < 0)
+	if (pmc_allocate(counter_name, PMC_MODE_SC, 0, 0, &pmcid, 64*1024) < 0)
 		err(EX_OSERR, "failed to allocate %s as a system counter in counting mode",
 		    counter_name);