summaryrefslogtreecommitdiff
path: root/tools/testing/selftests/rcutorture/bin/kvm.sh
blob: 6eb1d3f6524d587087e102b2dae809d7bc1b4fa5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
#!/bin/bash
# SPDX-License-Identifier: GPL-2.0+
#
# Run a series of tests under KVM.  By default, this series is specified
# by the relevant CFLIST file, but can be overridden by the --configs
# command-line argument.
#
# Usage: kvm.sh [ options ]
#
# Copyright (C) IBM Corporation, 2011
#
# Authors: Paul E. McKenney <paulmck@linux.ibm.com>

scriptname=$0
args="$*"

T=${TMPDIR-/tmp}/kvm.sh.$$
trap 'rm -rf $T' 0
mkdir $T

cd `dirname $scriptname`/../../../../../

dur=$((30*60))
dryrun=""
KVM="`pwd`/tools/testing/selftests/rcutorture"; export KVM
PATH=${KVM}/bin:$PATH; export PATH
. functions.sh

TORTURE_ALLOTED_CPUS="`identify_qemu_vcpus`"
TORTURE_DEFCONFIG=defconfig
TORTURE_BOOT_IMAGE=""
TORTURE_INITRD="$KVM/initrd"; export TORTURE_INITRD
TORTURE_KCONFIG_ARG=""
TORTURE_KCONFIG_GDB_ARG=""
TORTURE_BOOT_GDB_ARG=""
TORTURE_QEMU_GDB_ARG=""
TORTURE_KCONFIG_KASAN_ARG=""
TORTURE_KCONFIG_KCSAN_ARG=""
TORTURE_KMAKE_ARG=""
TORTURE_QEMU_MEM=512
TORTURE_SHUTDOWN_GRACE=180
TORTURE_SUITE=rcu
TORTURE_TRUST_MAKE=""
resdir=""
configs=""
cpus=0
ds=`date +%Y.%m.%d-%H.%M.%S`
jitter="-1"

usage () {
	echo "Usage: $scriptname optional arguments:"
	echo "       --allcpus"
	echo "       --bootargs kernel-boot-arguments"
	echo "       --bootimage relative-path-to-kernel-boot-image"
	echo "       --buildonly"
	echo "       --configs \"config-file list w/ repeat factor (3*TINY01)\""
	echo "       --cpus N"
	echo "       --datestamp string"
	echo "       --defconfig string"
	echo "       --dryrun sched|script"
	echo "       --duration minutes"
	echo "       --gdb"
	echo "       --help"
	echo "       --interactive"
	echo "       --jitter N [ maxsleep (us) [ maxspin (us) ] ]"
	echo "       --kconfig Kconfig-options"
	echo "       --kmake-arg kernel-make-arguments"
	echo "       --mac nn:nn:nn:nn:nn:nn"
	echo "       --memory megabytes|nnnG"
	echo "       --no-initrd"
	echo "       --qemu-args qemu-arguments"
	echo "       --qemu-cmd qemu-system-..."
	echo "       --results absolute-pathname"
	echo "       --torture lock|rcu|rcuscale|refscale|scf"
	echo "       --trust-make"
	exit 1
}

while test $# -gt 0
do
	case "$1" in
	--allcpus)
		cpus=$TORTURE_ALLOTED_CPUS
		max_cpus=$TORTURE_ALLOTED_CPUS
		;;
	--bootargs|--bootarg)
		checkarg --bootargs "(list of kernel boot arguments)" "$#" "$2" '.*' '^--'
		TORTURE_BOOTARGS="$2"
		shift
		;;
	--bootimage)
		checkarg --bootimage "(relative path to kernel boot image)" "$#" "$2" '[a-zA-Z0-9][a-zA-Z0-9_]*' '^--'
		TORTURE_BOOT_IMAGE="$2"
		shift
		;;
	--buildonly)
		TORTURE_BUILDONLY=1
		;;
	--configs|--config)
		checkarg --configs "(list of config files)" "$#" "$2" '^[^/]*$' '^--'
		configs="$2"
		shift
		;;
	--cpus)
		checkarg --cpus "(number)" "$#" "$2" '^[0-9]*$' '^--'
		cpus=$2
		TORTURE_ALLOTED_CPUS="$2"
		max_cpus="`identify_qemu_vcpus`"
		if test "$TORTURE_ALLOTED_CPUS" -gt "$max_cpus"
		then
			TORTURE_ALLOTED_CPUS=$max_cpus
		fi
		shift
		;;
	--datestamp)
		checkarg --datestamp "(relative pathname)" "$#" "$2" '^[^/]*$' '^--'
		ds=$2
		shift
		;;
	--defconfig)
		checkarg --defconfig "defconfigtype" "$#" "$2" '^[^/][^/]*$' '^--'
		TORTURE_DEFCONFIG=$2
		shift
		;;
	--dryrun)
		checkarg --dryrun "sched|script" $# "$2" 'sched\|script' '^--'
		dryrun=$2
		shift
		;;
	--duration)
		checkarg --duration "(minutes)" $# "$2" '^[0-9]*$' '^error'
		dur=$(($2*60))
		shift
		;;
	--gdb)
		TORTURE_KCONFIG_GDB_ARG="CONFIG_DEBUG_INFO=y"; export TORTURE_KCONFIG_GDB_ARG
		TORTURE_BOOT_GDB_ARG="nokaslr"; export TORTURE_BOOT_GDB_ARG
		TORTURE_QEMU_GDB_ARG="-s -S"; export TORTURE_QEMU_GDB_ARG
		;;
	--help|-h)
		usage
		;;
	--interactive)
		TORTURE_QEMU_INTERACTIVE=1; export TORTURE_QEMU_INTERACTIVE
		;;
	--jitter)
		checkarg --jitter "(# threads [ sleep [ spin ] ])" $# "$2" '^-\{,1\}[0-9]\+\( \+[0-9]\+\)\{,2\} *$' '^error$'
		jitter="$2"
		shift
		;;
	--kconfig)
		checkarg --kconfig "(Kconfig options)" $# "$2" '^CONFIG_[A-Z0-9_]\+=\([ynm]\|[0-9]\+\)\( CONFIG_[A-Z0-9_]\+=\([ynm]\|[0-9]\+\)\)*$' '^error$'
		TORTURE_KCONFIG_ARG="$2"
		shift
		;;
	--kasan)
		TORTURE_KCONFIG_KASAN_ARG="CONFIG_DEBUG_INFO=y CONFIG_KASAN=y"; export TORTURE_KCONFIG_KASAN_ARG
		;;
	--kcsan)
		TORTURE_KCONFIG_KCSAN_ARG="CONFIG_DEBUG_INFO=y CONFIG_KCSAN=y CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY=n CONFIG_KCSAN_REPORT_ONCE_IN_MS=100000 CONFIG_KCSAN_VERBOSE=y CONFIG_KCSAN_INTERRUPT_WATCHER=y"; export TORTURE_KCONFIG_KCSAN_ARG
		;;
	--kmake-arg)
		checkarg --kmake-arg "(kernel make arguments)" $# "$2" '.*' '^error$'
		TORTURE_KMAKE_ARG="$2"
		shift
		;;
	--mac)
		checkarg --mac "(MAC address)" $# "$2" '^\([0-9a-fA-F]\{2\}:\)\{5\}[0-9a-fA-F]\{2\}$' error
		TORTURE_QEMU_MAC=$2
		shift
		;;
	--memory)
		checkarg --memory "(memory size)" $# "$2" '^[0-9]\+[MG]\?$' error
		TORTURE_QEMU_MEM=$2
		shift
		;;
	--no-initrd)
		TORTURE_INITRD=""; export TORTURE_INITRD
		;;
	--qemu-args|--qemu-arg)
		checkarg --qemu-args "(qemu arguments)" $# "$2" '^-' '^error'
		TORTURE_QEMU_ARG="$2"
		shift
		;;
	--qemu-cmd)
		checkarg --qemu-cmd "(qemu-system-...)" $# "$2" 'qemu-system-' '^--'
		TORTURE_QEMU_CMD="$2"
		shift
		;;
	--results)
		checkarg --results "(absolute pathname)" "$#" "$2" '^/' '^error'
		resdir=$2
		shift
		;;
	--shutdown-grace)
		checkarg --shutdown-grace "(seconds)" "$#" "$2" '^[0-9]*$' '^error'
		TORTURE_SHUTDOWN_GRACE=$2
		shift
		;;
	--torture)
		checkarg --torture "(suite name)" "$#" "$2" '^\(lock\|rcu\|rcuscale\|refscale\|scf\)$' '^--'
		TORTURE_SUITE=$2
		shift
		if test "$TORTURE_SUITE" = rcuscale || test "$TORTURE_SUITE" = refscale
		then
			# If you really want jitter for refscale or
			# rcuscale, specify it after specifying the rcuscale
			# or the refscale.  (But why jitter in these cases?)
			jitter=0
		fi
		;;
	--trust-make)
		TORTURE_TRUST_MAKE="y"
		;;
	*)
		echo Unknown argument $1
		usage
		;;
	esac
	shift
done

if test -z "$TORTURE_INITRD" || tools/testing/selftests/rcutorture/bin/mkinitrd.sh
then
	:
else
	echo No initrd and unable to create one, aborting test >&2
	exit 1
fi

CONFIGFRAG=${KVM}/configs/${TORTURE_SUITE}; export CONFIGFRAG

defaultconfigs="`tr '\012' ' ' < $CONFIGFRAG/CFLIST`"
if test -z "$configs"
then
	configs=$defaultconfigs
fi

if test -z "$resdir"
then
	resdir=$KVM/res
fi

# Create a file of test-name/#cpus pairs, sorted by decreasing #cpus.
configs_derep=
for CF in $configs
do
	case $CF in
	[0-9]\**|[0-9][0-9]\**|[0-9][0-9][0-9]\**)
		config_reps=`echo $CF | sed -e 's/\*.*$//'`
		CF1=`echo $CF | sed -e 's/^[^*]*\*//'`
		;;
	*)
		config_reps=1
		CF1=$CF
		;;
	esac
	for ((cur_rep=0;cur_rep<$config_reps;cur_rep++))
	do
		configs_derep="$configs_derep $CF1"
	done
done
touch $T/cfgcpu
configs_derep="`echo $configs_derep | sed -e "s/\<CFLIST\>/$defaultconfigs/g"`"
if test -n "$TORTURE_KCONFIG_GDB_ARG"
then
	if test "`echo $configs_derep | wc -w`" -gt 1
	then
		echo "The --config list is: $configs_derep."
		echo "Only one --config permitted with --gdb, terminating."
		exit 1
	fi
fi
for CF1 in $configs_derep
do
	if test -f "$CONFIGFRAG/$CF1"
	then
		cpu_count=`configNR_CPUS.sh $CONFIGFRAG/$CF1`
		cpu_count=`configfrag_boot_cpus "$TORTURE_BOOTARGS" "$CONFIGFRAG/$CF1" "$cpu_count"`
		cpu_count=`configfrag_boot_maxcpus "$TORTURE_BOOTARGS" "$CONFIGFRAG/$CF1" "$cpu_count"`
		echo $CF1 $cpu_count >> $T/cfgcpu
	else
		echo "The --configs file $CF1 does not exist, terminating."
		exit 1
	fi
done
sort -k2nr $T/cfgcpu -T="$T" > $T/cfgcpu.sort

# Use a greedy bin-packing algorithm, sorting the list accordingly.
awk < $T/cfgcpu.sort > $T/cfgcpu.pack -v ncpus=$cpus '
BEGIN {
	njobs = 0;
}

{
	# Read file of tests and corresponding required numbers of CPUs.
	cf[njobs] = $1;
	cpus[njobs] = $2;
	njobs++;
}

END {
	batch = 0;
	nc = -1;

	# Each pass through the following loop creates on test batch
	# that can be executed concurrently given ncpus.  Note that a
	# given test that requires more than the available CPUs will run in
	# their own batch.  Such tests just have to make do with what
	# is available.
	while (nc != ncpus) {
		batch++;
		nc = ncpus;

		# Each pass through the following loop considers one
		# test for inclusion in the current batch.
		for (i = 0; i < njobs; i++) {
			if (done[i])
				continue; # Already part of a batch.
			if (nc >= cpus[i] || nc == ncpus) {

				# This test fits into the current batch.
				done[i] = batch;
				nc -= cpus[i];
				if (nc <= 0)
					break; # Too-big test in its own batch.
			}
		}
	}

	# Dump out the tests in batch order.
	for (b = 1; b <= batch; b++)
		for (i = 0; i < njobs; i++)
			if (done[i] == b)
				print cf[i], cpus[i];
}'

# Generate a script to execute the tests in appropriate batches.
cat << ___EOF___ > $T/script
CONFIGFRAG="$CONFIGFRAG"; export CONFIGFRAG
KVM="$KVM"; export KVM
PATH="$PATH"; export PATH
TORTURE_ALLOTED_CPUS="$TORTURE_ALLOTED_CPUS"; export TORTURE_ALLOTED_CPUS
TORTURE_BOOT_IMAGE="$TORTURE_BOOT_IMAGE"; export TORTURE_BOOT_IMAGE
TORTURE_BUILDONLY="$TORTURE_BUILDONLY"; export TORTURE_BUILDONLY
TORTURE_DEFCONFIG="$TORTURE_DEFCONFIG"; export TORTURE_DEFCONFIG
TORTURE_INITRD="$TORTURE_INITRD"; export TORTURE_INITRD
TORTURE_KCONFIG_ARG="$TORTURE_KCONFIG_ARG"; export TORTURE_KCONFIG_ARG
TORTURE_KCONFIG_GDB_ARG="$TORTURE_KCONFIG_GDB_ARG"; export TORTURE_KCONFIG_GDB_ARG
TORTURE_BOOT_GDB_ARG="$TORTURE_BOOT_GDB_ARG"; export TORTURE_BOOT_GDB_ARG
TORTURE_QEMU_GDB_ARG="$TORTURE_QEMU_GDB_ARG"; export TORTURE_QEMU_GDB_ARG
TORTURE_KCONFIG_KASAN_ARG="$TORTURE_KCONFIG_KASAN_ARG"; export TORTURE_KCONFIG_KASAN_ARG
TORTURE_KCONFIG_KCSAN_ARG="$TORTURE_KCONFIG_KCSAN_ARG"; export TORTURE_KCONFIG_KCSAN_ARG
TORTURE_KMAKE_ARG="$TORTURE_KMAKE_ARG"; export TORTURE_KMAKE_ARG
TORTURE_QEMU_CMD="$TORTURE_QEMU_CMD"; export TORTURE_QEMU_CMD
TORTURE_QEMU_INTERACTIVE="$TORTURE_QEMU_INTERACTIVE"; export TORTURE_QEMU_INTERACTIVE
TORTURE_QEMU_MAC="$TORTURE_QEMU_MAC"; export TORTURE_QEMU_MAC
TORTURE_QEMU_MEM="$TORTURE_QEMU_MEM"; export TORTURE_QEMU_MEM
TORTURE_SHUTDOWN_GRACE="$TORTURE_SHUTDOWN_GRACE"; export TORTURE_SHUTDOWN_GRACE
TORTURE_SUITE="$TORTURE_SUITE"; export TORTURE_SUITE
TORTURE_TRUST_MAKE="$TORTURE_TRUST_MAKE"; export TORTURE_TRUST_MAKE
if ! test -e $resdir
then
	mkdir -p "$resdir" || :
fi
mkdir $resdir/$ds
TORTURE_RESDIR="$resdir/$ds"; export TORTURE_RESDIR
TORTURE_STOPFILE="$resdir/$ds/STOP"; export TORTURE_STOPFILE
echo Results directory: $resdir/$ds
echo $scriptname $args
touch $resdir/$ds/log
echo $scriptname $args >> $resdir/$ds/log
echo ${TORTURE_SUITE} > $resdir/$ds/TORTURE_SUITE
pwd > $resdir/$ds/testid.txt
if test -d .git
then
	git status >> $resdir/$ds/testid.txt
	git rev-parse HEAD >> $resdir/$ds/testid.txt
	git diff HEAD >> $resdir/$ds/testid.txt
fi
___EOF___
awk < $T/cfgcpu.pack \
	-v TORTURE_BUILDONLY="$TORTURE_BUILDONLY" \
	-v CONFIGDIR="$CONFIGFRAG/" \
	-v KVM="$KVM" \
	-v ncpus=$cpus \
	-v jitter="$jitter" \
	-v rd=$resdir/$ds/ \
	-v dur=$dur \
	-v TORTURE_QEMU_ARG="$TORTURE_QEMU_ARG" \
	-v TORTURE_BOOTARGS="$TORTURE_BOOTARGS" \
'BEGIN {
	i = 0;
}

{
	cf[i] = $1;
	cpus[i] = $2;
	i++;
}

# Dump out the scripting required to run one test batch.
function dump(first, pastlast, batchnum)
{
	print "echo ----Start batch " batchnum ": `date` | tee -a " rd "log";
	print "needqemurun="
	jn=1
	for (j = first; j < pastlast; j++) {
		builddir=KVM "/b" j - first + 1
		cpusr[jn] = cpus[j];
		if (cfrep[cf[j]] == "") {
			cfr[jn] = cf[j];
			cfrep[cf[j]] = 1;
		} else {
			cfrep[cf[j]]++;
			cfr[jn] = cf[j] "." cfrep[cf[j]];
		}
		if (cpusr[jn] > ncpus && ncpus != 0)
			ovf = "-ovf";
		else
			ovf = "";
		print "echo ", cfr[jn], cpusr[jn] ovf ": Starting build. `date` | tee -a " rd "log";
		print "rm -f " builddir ".*";
		print "touch " builddir ".wait";
		print "mkdir " rd cfr[jn] " || :";
		print "kvm-test-1-run.sh " CONFIGDIR cf[j], builddir, rd cfr[jn], dur " \"" TORTURE_QEMU_ARG "\" \"" TORTURE_BOOTARGS "\" > " rd cfr[jn]  "/kvm-test-1-run.sh.out 2>&1 &"
		print "echo ", cfr[jn], cpusr[jn] ovf ": Waiting for build to complete. `date` | tee -a " rd "log";
		print "while test -f " builddir ".wait"
		print "do"
		print "\tsleep 1"
		print "done"
		print "echo ", cfr[jn], cpusr[jn] ovf ": Build complete. `date` | tee -a " rd "log";
		jn++;
	}
	for (j = 1; j < jn; j++) {
		builddir=KVM "/b" j
		print "rm -f " builddir ".ready"
		print "if test -f \"" rd cfr[j] "/builtkernel\""
		print "then"
		print "\techo ----", cfr[j], cpusr[j] ovf ": Kernel present. `date` | tee -a " rd "log";
		print "\tneedqemurun=1"
		print "fi"
	}
	njitter = 0;
	split(jitter, ja);
	if (ja[1] == -1 && ncpus == 0)
		njitter = 1;
	else if (ja[1] == -1)
		njitter = ncpus;
	else
		njitter = ja[1];
	if (TORTURE_BUILDONLY && njitter != 0) {
		njitter = 0;
		print "echo Build-only run, so suppressing jitter | tee -a " rd "log"
	}
	if (TORTURE_BUILDONLY) {
		print "needqemurun="
	}
	print "if test -n \"$needqemurun\""
	print "then"
	print "\techo ---- Starting kernels. `date` | tee -a " rd "log";
	for (j = 0; j < njitter; j++)
		print "\tjitter.sh " j " " dur " " ja[2] " " ja[3] "&"
	print "\twait"
	print "\techo ---- All kernel runs complete. `date` | tee -a " rd "log";
	print "else"
	print "\twait"
	print "\techo ---- No kernel runs. `date` | tee -a " rd "log";
	print "fi"
	for (j = 1; j < jn; j++) {
		builddir=KVM "/b" j
		print "echo ----", cfr[j], cpusr[j] ovf ": Build/run results: | tee -a " rd "log";
		print "cat " rd cfr[j]  "/kvm-test-1-run.sh.out | tee -a " rd "log";
	}
}

END {
	njobs = i;
	nc = ncpus;
	first = 0;
	batchnum = 1;

	# Each pass through the following loop considers one test.
	for (i = 0; i < njobs; i++) {
		if (ncpus == 0) {
			# Sequential test specified, each test its own batch.
			dump(i, i + 1, batchnum);
			first = i;
			batchnum++;
		} else if (nc < cpus[i] && i != 0) {
			# Out of CPUs, dump out a batch.
			dump(first, i, batchnum);
			first = i;
			nc = ncpus;
			batchnum++;
		}
		# Account for the CPUs needed by the current test.
		nc -= cpus[i];
	}
	# Dump the last batch.
	if (ncpus != 0)
		dump(first, i, batchnum);
}' >> $T/script

cat << ___EOF___ >> $T/script
echo
echo
echo " --- `date` Test summary:"
echo Results directory: $resdir/$ds
kcsan-collapse.sh $resdir/$ds
kvm-recheck.sh $resdir/$ds
___EOF___

if test "$dryrun" = script
then
	cat $T/script
	exit 0
elif test "$dryrun" = sched
then
	# Extract the test run schedule from the script.
	egrep 'Start batch|Starting build\.' $T/script |
		grep -v ">>" |
		sed -e 's/:.*$//' -e 's/^echo //'
	exit 0
else
	# Not a dryrun, so run the script.
	sh $T/script
fi

# Tracing: trace_event=rcu:rcu_grace_period,rcu:rcu_future_grace_period,rcu:rcu_grace_period_init,rcu:rcu_nocb_wake,rcu:rcu_preempt_task,rcu:rcu_unlock_preempted_task,rcu:rcu_quiescent_state_report,rcu:rcu_fqs,rcu:rcu_callback,rcu:rcu_kfree_callback,rcu:rcu_batch_start,rcu:rcu_invoke_callback,rcu:rcu_invoke_kfree_callback,rcu:rcu_batch_end,rcu:rcu_torture_read,rcu:rcu_barrier
# Function-graph tracing: ftrace=function_graph ftrace_graph_filter=sched_setaffinity,migration_cpu_stop
# Also --kconfig "CONFIG_FUNCTION_TRACER=y CONFIG_FUNCTION_GRAPH_TRACER=y"
# Control buffer size: --bootargs trace_buf_size=3k
# Get trace-buffer dumps on all oopses: --bootargs ftrace_dump_on_oops
# Ditto, but dump only the oopsing CPU: --bootargs ftrace_dump_on_oops=orig_cpu
# Heavy-handed way to also dump on warnings: --bootargs panic_on_warn