Trace number 3372799

Some explanations

A solver is run under the control of another program named runsolver. runsolver is in charge of imposing the CPU time limit and the memory limit to the solver. It also monitors some information about the process. The trace of the execution of a solver is divided into four (or five) parts:
  1. SOLVER DATA
    This is the output of the solver (stdout and stderr).
    Note that some very long lines in this section may be truncated by your web browser ! In such a case, you may want to use the "Download as text" link to get the trace as a text file.

    When the --timestamp option is passed to the runsolver program, each line output by the solver is prepended with a timestamp which indicates at what time the line was output by the solver. Times are relative to the start of the program, given in seconds. The first timestamp (if present) is estimated CPU time. The last timestamp is wall clock time.

    As some 'v lines' may be very long (sometimes several megabytes), the 'v line' output by your solver may be split on several lines to help limit the size of the trace recorded in the database. In any case, the exact output of your solver is preserved in a trace file.
  2. VERIFIER DATA
    The output of the solver is piped to a verifier program which will search a value line "v " and, if found, will check that the given interpretation satisfies all constraints.
  3. CONVERSION SCRIPT DATA (Optionnal)
    When a conversion script is used, this section shows the messages that were output by the conversion script.
  4. WATCHER DATA
    This is the informations gathered by the runsolver program. It first prints the different limits. There's a first limit on CPU time set to X seconds (see the parameters in the trace). After this time has ellapsed, runsolver sends a SIGTERM and 2 seconds later a SIGKILL to the solver. For safety, there's also another limit set to X+30 seconds which will send a SIGXPU to the solver. The last limit is on the virtual memory used by the process (see the parameters in the trace).
    Every ten seconds, the runsolver process fetches the content of /proc/loadavg, /proc/pid/stat and /proc/pid/statm (see man proc) and prints it as raw data. This is only recorded in case we need to investigate the behaviour of a solver. The memory used by the solver (vsize) is also given every ten seconds.
    When the solver exits, runsolver prints some informations such as status and time. CPU usage is the ratio CPU Time/Real Time.
  5. LAUNCHER DATA
    These informations are related to the script which will launch the solver. The most important informations are the command line given to the solver, the md5sum of the different files and the dump of the /proc/cpuinfo and /proc/meminfo which provides some useful information on the computer.

Solver answer on this benchmark

Solver NameAnswerCPU timeWall clock time
Lingeling 587f (fixed)UNSAT 10.6424 10.6453

General information on the benchmark

Nameapplication/leberre/
2dimensionalstrippacking/E05X15.cnf
MD5SUMe53b8f4e61e6411a209ad63833d35585
Bench CategoryAPPLICATION (applications instances)
Best result obtained on this benchmarkUNSAT
Best CPU time to get the best result obtained on this benchmark4.66929
Satisfiable
(Un)Satisfiability was proved
Number of variables4740
Number of clauses41379
Sum of the clauses size183934
Maximum clause length45
Minimum clause length1
Number of clauses of size 17
Number of clauses of size 211966
Number of clauses of size 39700
Number of clauses of size 43195
Number of clauses of size 54425
Number of clauses of size over 512086

Solver Data 

10.59/10.64	s UNSATISFIABLE

Verifier Data 

No possible verification on an UNSAT instance

Watcher Data 

runsolver Copyright (C) 2010-2011 Olivier ROUSSEL

This is runsolver version 3.3.0 (svn: 961)

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

command line: BIN/runsolver --timestamp -w /tmp/evaluation-result-3372799-1305426017/watcher-3372799-1305426017 -o /tmp/evaluation-result-3372799-1305426017/solver-3372799-1305426017 -C 5000 -W 5100 -M 15500 lingeling HOME/instance-3372799-1305426017.cnf 

running on 4 cores: 0,2,4,6

Enforcing CPUTime limit (soft limit, will send SIGTERM then SIGKILL): 5000 seconds
Enforcing CPUTime limit (hard limit, will send SIGXCPU): 5030 seconds
Enforcing wall clock limit (soft limit, will send SIGTERM then SIGKILL): 5100 seconds
Enforcing VSIZE limit (soft limit, will send SIGTERM then SIGKILL): 15872000 KiB
Enforcing VSIZE limit (hard limit, stack expansion will fail with SIGSEGV, brk() and mmap() will return ENOMEM): 15923200 KiB
Current StackSize limit: 10240 KiB


[startup+0 s]
/proc/loadavg: 3.45 5.69 7.26 2/298 21384
/proc/meminfo: memFree=12014200/32951124 swapFree=66050672/67111528
[pid=21384] ppid=21382 vsize=7812 CPUtime=0 cores=0,2,4,6
/proc/21384/stat : 21384 (lingeling) R 21382 21384 18486 0 -1 4202496 534 0 0 0 0 0 0 0 23 0 1 0 654199553 7999488 477 33554432000 4194304 4409284 140736443175632 18446744073709551615 255377301248 0 0 4096 17506 0 0 0 17 4 0 0 0
/proc/21384/statm: 1953 477 113 53 0 376 0

[startup+0.106116 s]
/proc/loadavg: 3.45 5.69 7.26 2/298 21384
/proc/meminfo: memFree=12014200/32951124 swapFree=66050672/67111528
[pid=21384] ppid=21382 vsize=9808 CPUtime=0.1 cores=0,2,4,6
/proc/21384/stat : 21384 (lingeling) R 21382 21384 18486 0 -1 4202496 1221 0 0 0 10 0 0 0 23 0 1 0 654199553 10043392 986 33554432000 4194304 4409284 140736443175632 18446744073709551615 4299704 0 0 4096 17506 0 0 0 17 4 0 0 0
/proc/21384/statm: 2452 986 128 53 0 875 0
Current children cumulated CPU time (s) 0.1
Current children cumulated vsize (KiB) 9808

[startup+0.201098 s]
/proc/loadavg: 3.45 5.69 7.26 2/298 21384
/proc/meminfo: memFree=12014200/32951124 swapFree=66050672/67111528
[pid=21384] ppid=21382 vsize=9808 CPUtime=0.19 cores=0,2,4,6
/proc/21384/stat : 21384 (lingeling) R 21382 21384 18486 0 -1 4202496 1223 0 0 0 19 0 0 0 23 0 1 0 654199553 10043392 988 33554432000 4194304 4409284 140736443175632 18446744073709551615 4272098 0 0 4096 17506 0 0 0 17 4 0 0 0
/proc/21384/statm: 2452 988 130 53 0 875 0
Current children cumulated CPU time (s) 0.19
Current children cumulated vsize (KiB) 9808

[startup+0.301092 s]
/proc/loadavg: 3.45 5.69 7.26 2/298 21384
/proc/meminfo: memFree=12014200/32951124 swapFree=66050672/67111528
[pid=21384] ppid=21382 vsize=10260 CPUtime=0.29 cores=0,2,4,6
/proc/21384/stat : 21384 (lingeling) R 21382 21384 18486 0 -1 4202496 1337 0 0 0 29 0 0 0 23 0 1 0 654199553 10506240 1102 33554432000 4194304 4409284 140736443175632 18446744073709551615 4269759 0 0 4096 17506 0 0 0 17 4 0 0 0
/proc/21384/statm: 2565 1102 131 53 0 988 0
Current children cumulated CPU time (s) 0.29
Current children cumulated vsize (KiB) 10260

[startup+0.701031 s]
/proc/loadavg: 3.45 5.69 7.26 2/298 21384
/proc/meminfo: memFree=12014200/32951124 swapFree=66050672/67111528
[pid=21384] ppid=21382 vsize=9948 CPUtime=0.69 cores=0,2,4,6
/proc/21384/stat : 21384 (lingeling) R 21382 21384 18486 0 -1 4202496 1725 0 0 0 69 0 0 0 25 0 1 0 654199553 10186752 1002 33554432000 4194304 4409284 140736443175632 18446744073709551615 4242758 0 0 4096 17506 0 0 0 17 4 0 0 0
/proc/21384/statm: 2487 1002 136 53 0 910 0
Current children cumulated CPU time (s) 0.69
Current children cumulated vsize (KiB) 9948

[startup+1.50089 s]
/proc/loadavg: 3.45 5.69 7.26 3/302 21391
/proc/meminfo: memFree=11997312/32951124 swapFree=66050672/67111528
[pid=21384] ppid=21382 vsize=11152 CPUtime=1.49 cores=0,2,4,6
/proc/21384/stat : 21384 (lingeling) R 21382 21384 18486 0 -1 4202496 2031 0 0 0 149 0 0 0 25 0 1 0 654199553 11419648 1308 33554432000 4194304 4409284 140736443175632 18446744073709551615 255377325975 0 0 4096 17506 0 0 0 17 4 0 0 0
/proc/21384/statm: 2788 1308 141 53 0 1211 0
Current children cumulated CPU time (s) 1.49
Current children cumulated vsize (KiB) 11152

[startup+3.10058 s]
/proc/loadavg: 3.45 5.69 7.26 3/302 21391
/proc/meminfo: memFree=11994124/32951124 swapFree=66050672/67111528
[pid=21384] ppid=21382 vsize=14632 CPUtime=3.09 cores=0,2,4,6
/proc/21384/stat : 21384 (lingeling) R 21382 21384 18486 0 -1 4202496 4098 0 0 0 307 2 0 0 25 0 1 0 654199553 14983168 2186 33554432000 4194304 4409284 140736443175632 18446744073709551615 4330509 0 0 4096 17506 0 0 0 17 4 0 0 0
/proc/21384/statm: 3658 2186 141 53 0 2081 0
Current children cumulated CPU time (s) 3.09
Current children cumulated vsize (KiB) 14632

[startup+6.30097 s]
/proc/loadavg: 3.33 5.63 7.23 2/299 21412
/proc/meminfo: memFree=11894432/32951124 swapFree=66050672/67111528
[pid=21384] ppid=21382 vsize=18224 CPUtime=6.29 cores=0,2,4,6
/proc/21384/stat : 21384 (lingeling) R 21382 21384 18486 0 -1 4202496 6070 0 0 0 625 4 0 0 25 0 1 0 654199553 18661376 3084 33554432000 4194304 4409284 140736443175632 18446744073709551615 255377325975 0 0 4096 17506 0 0 0 17 0 0 0 0
/proc/21384/statm: 4556 3084 141 53 0 2979 0
Current children cumulated CPU time (s) 6.29
Current children cumulated vsize (KiB) 18224

Solver just ended. Dumping a history of the last processes samples

[startup+6.40095 s]
/proc/loadavg: 3.33 5.63 7.23 2/299 21412
/proc/meminfo: memFree=11894432/32951124 swapFree=66050672/67111528
[pid=21384] ppid=21382 vsize=18224 CPUtime=6.38 cores=0,2,4,6
/proc/21384/stat : 21384 (lingeling) R 21382 21384 18486 0 -1 4202496 6070 0 0 0 634 4 0 0 25 0 1 0 654199553 18661376 3084 33554432000 4194304 4409284 140736443175632 18446744073709551615 4358519 0 0 4096 17506 0 0 0 17 0 0 0 0
/proc/21384/statm: 4556 3084 141 53 0 2979 0
Current children cumulated CPU time (s) 6.38
Current children cumulated vsize (KiB) 18224

[startup+8.0007 s]
/proc/loadavg: 3.33 5.63 7.23 3/302 21418
/proc/meminfo: memFree=11762752/32951124 swapFree=66050672/67111528
[pid=21384] ppid=21382 vsize=17824 CPUtime=7.99 cores=0,2,4,6
/proc/21384/stat : 21384 (lingeling) R 21382 21384 18486 0 -1 4202496 6820 0 0 0 793 6 0 0 25 0 1 0 654199553 18251776 2984 33554432000 4194304 4409284 140736443175632 18446744073709551615 255377325975 0 0 4096 17506 0 0 0 17 0 0 0 0
/proc/21384/statm: 4456 2984 141 53 0 2879 0
Current children cumulated CPU time (s) 7.99
Current children cumulated vsize (KiB) 17824

[startup+9.6004 s]
/proc/loadavg: 3.23 5.57 7.20 3/302 21418
/proc/meminfo: memFree=11750856/32951124 swapFree=66050672/67111528
[pid=21384] ppid=21382 vsize=15336 CPUtime=9.59 cores=0,2,4,6
/proc/21384/stat : 21384 (lingeling) R 21382 21384 18486 0 -1 4202496 7660 0 0 0 952 7 0 0 25 0 1 0 654199553 15704064 2362 33554432000 4194304 4409284 140736443175632 18446744073709551615 4301335 0 0 4096 17506 0 0 0 17 0 0 0 0
/proc/21384/statm: 3834 2362 141 53 0 2257 0
Current children cumulated CPU time (s) 9.59
Current children cumulated vsize (KiB) 15336

[startup+10.4003 s]
/proc/loadavg: 3.23 5.57 7.20 3/302 21418
/proc/meminfo: memFree=11750112/32951124 swapFree=66050672/67111528
[pid=21384] ppid=21382 vsize=12648 CPUtime=10.39 cores=0,2,4,6
/proc/21384/stat : 21384 (lingeling) R 21382 21384 18486 0 -1 4202496 7763 0 0 0 1032 7 0 0 25 0 1 0 654199553 12951552 1690 33554432000 4194304 4409284 140736443175632 18446744073709551615 255377325975 0 0 4096 17506 0 0 0 17 0 0 0 0
/proc/21384/statm: 3162 1690 141 53 0 1585 0
Current children cumulated CPU time (s) 10.39
Current children cumulated vsize (KiB) 12648

[startup+10.6002 s]
/proc/loadavg: 3.23 5.57 7.20 3/302 21418
/proc/meminfo: memFree=11750112/32951124 swapFree=66050672/67111528
[pid=21384] ppid=21382 vsize=12796 CPUtime=10.59 cores=0,2,4,6
/proc/21384/stat : 21384 (lingeling) R 21382 21384 18486 0 -1 4202496 7800 0 0 0 1052 7 0 0 25 0 1 0 654199553 13103104 1727 33554432000 4194304 4409284 140736443175632 18446744073709551615 255377325975 0 0 4096 17506 0 0 0 17 0 0 0 0
/proc/21384/statm: 3199 1727 141 53 0 1622 0
Current children cumulated CPU time (s) 10.59
Current children cumulated vsize (KiB) 12796

Child status: 20
Real time (s): 10.6453
CPU time (s): 10.6424
CPU user time (s): 10.5664
CPU system time (s): 0.075988
CPU usage (%): 99.9728
Max. virtual memory (cumulated for all children) (KiB): 18224

getrusage(RUSAGE_CHILDREN,...) data:
user time used= 10.5664
system time used= 0.075988
maximum resident set size= 0
integral shared memory size= 0
integral unshared data size= 0
integral unshared stack size= 0
page reclaims= 7877
page faults= 0
swaps= 0
block input operations= 0
block output operations= 0
messages sent= 0
messages received= 0
signals received= 0
voluntary context switches= 4
involuntary context switches= 117

runsolver used 0.027995 second user time and 0.073988 second system time

The end

Launcher Data 

Begin job on node135 at 2011-05-15 04:20:17
IDJOB=3372799
IDBENCH=83454
IDSOLVER=1850
FILE ID=node135/3372799-1305426017
RUNJOBID= node135-1305426017-21370
PBS_JOBID= 13324578
Free space on /tmp= 73368 MiB

SOLVER NAME= Lingeling 587f (fixed)
BENCH NAME= SAT11/application/leberre/2dimensionalstrippacking/E05X15.cnf
COMMAND LINE= lingeling BENCHNAME
RUNSOLVER COMMAND LINE= BIN/runsolver --timestamp -w /tmp/evaluation-result-3372799-1305426017/watcher-3372799-1305426017 -o /tmp/evaluation-result-3372799-1305426017/solver-3372799-1305426017 -C 5000 -W 5100 -M 15500  lingeling HOME/instance-3372799-1305426017.cnf

TIME LIMIT= 5000 seconds
MEMORY LIMIT= 15500 MiB
NBCORE= 4

MD5SUM BENCH= e53b8f4e61e6411a209ad63833d35585
RANDOM SEED=891272517

node135.alineos.net Linux 2.6.18-164.el5 #1 SMP Thu Sep 3 03:28:30 EDT 2009

/proc/cpuinfo:
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 26
model name	: Intel(R) Xeon(R) CPU           X5550  @ 2.67GHz
stepping	: 5
cpu MHz		: 2666.851
cache size	: 8192 KB
physical id	: 0
siblings	: 4
core id		: 0
cpu cores	: 4
apicid		: 0
fpu		: yes
fpu_exception	: yes
cpuid level	: 11
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx rdtscp lm constant_tsc ida nonstop_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr popcnt lahf_lm
bogomips	: 5333.70
clflush size	: 64
cache_alignment	: 64
address sizes	: 40 bits physical, 48 bits virtual
power management: [8]

processor	: 1
vendor_id	: GenuineIntel
cpu family	: 6
model		: 26
model name	: Intel(R) Xeon(R) CPU           X5550  @ 2.67GHz
stepping	: 5
cpu MHz		: 2666.851
cache size	: 8192 KB
physical id	: 1
siblings	: 4
core id		: 0
cpu cores	: 4
apicid		: 16
fpu		: yes
fpu_exception	: yes
cpuid level	: 11
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx rdtscp lm constant_tsc ida nonstop_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr popcnt lahf_lm
bogomips	: 5332.83
clflush size	: 64
cache_alignment	: 64
address sizes	: 40 bits physical, 48 bits virtual
power management: [8]

processor	: 2
vendor_id	: GenuineIntel
cpu family	: 6
model		: 26
model name	: Intel(R) Xeon(R) CPU           X5550  @ 2.67GHz
stepping	: 5
cpu MHz		: 2666.851
cache size	: 8192 KB
physical id	: 0
siblings	: 4
core id		: 1
cpu cores	: 4
apicid		: 2
fpu		: yes
fpu_exception	: yes
cpuid level	: 11
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx rdtscp lm constant_tsc ida nonstop_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr popcnt lahf_lm
bogomips	: 5332.75
clflush size	: 64
cache_alignment	: 64
address sizes	: 40 bits physical, 48 bits virtual
power management: [8]

processor	: 3
vendor_id	: GenuineIntel
cpu family	: 6
model		: 26
model name	: Intel(R) Xeon(R) CPU           X5550  @ 2.67GHz
stepping	: 5
cpu MHz		: 2666.851
cache size	: 8192 KB
physical id	: 1
siblings	: 4
core id		: 1
cpu cores	: 4
apicid		: 18
fpu		: yes
fpu_exception	: yes
cpuid level	: 11
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx rdtscp lm constant_tsc ida nonstop_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr popcnt lahf_lm
bogomips	: 6640.14
clflush size	: 64
cache_alignment	: 64
address sizes	: 40 bits physical, 48 bits virtual
power management: [8]

processor	: 4
vendor_id	: GenuineIntel
cpu family	: 6
model		: 26
model name	: Intel(R) Xeon(R) CPU           X5550  @ 2.67GHz
stepping	: 5
cpu MHz		: 2666.851
cache size	: 8192 KB
physical id	: 0
siblings	: 4
core id		: 2
cpu cores	: 4
apicid		: 4
fpu		: yes
fpu_exception	: yes
cpuid level	: 11
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx rdtscp lm constant_tsc ida nonstop_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr popcnt lahf_lm
bogomips	: 5332.78
clflush size	: 64
cache_alignment	: 64
address sizes	: 40 bits physical, 48 bits virtual
power management: [8]

processor	: 5
vendor_id	: GenuineIntel
cpu family	: 6
model		: 26
model name	: Intel(R) Xeon(R) CPU           X5550  @ 2.67GHz
stepping	: 5
cpu MHz		: 2666.851
cache size	: 8192 KB
physical id	: 1
siblings	: 4
core id		: 2
cpu cores	: 4
apicid		: 20
fpu		: yes
fpu_exception	: yes
cpuid level	: 11
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx rdtscp lm constant_tsc ida nonstop_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr popcnt lahf_lm
bogomips	: 5332.75
clflush size	: 64
cache_alignment	: 64
address sizes	: 40 bits physical, 48 bits virtual
power management: [8]

processor	: 6
vendor_id	: GenuineIntel
cpu family	: 6
model		: 26
model name	: Intel(R) Xeon(R) CPU           X5550  @ 2.67GHz
stepping	: 5
cpu MHz		: 2666.851
cache size	: 8192 KB
physical id	: 0
siblings	: 4
core id		: 3
cpu cores	: 4
apicid		: 6
fpu		: yes
fpu_exception	: yes
cpuid level	: 11
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx rdtscp lm constant_tsc ida nonstop_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr popcnt lahf_lm
bogomips	: 5332.74
clflush size	: 64
cache_alignment	: 64
address sizes	: 40 bits physical, 48 bits virtual
power management: [8]

processor	: 7
vendor_id	: GenuineIntel
cpu family	: 6
model		: 26
model name	: Intel(R) Xeon(R) CPU           X5550  @ 2.67GHz
stepping	: 5
cpu MHz		: 2666.851
cache size	: 8192 KB
physical id	: 1
siblings	: 4
core id		: 3
cpu cores	: 4
apicid		: 22
fpu		: yes
fpu_exception	: yes
cpuid level	: 11
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx rdtscp lm constant_tsc ida nonstop_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr popcnt lahf_lm
bogomips	: 5332.76
clflush size	: 64
cache_alignment	: 64
address sizes	: 40 bits physical, 48 bits virtual
power management: [8]


/proc/meminfo:
MemTotal:     32951124 kB
MemFree:      12014356 kB
Buffers:        284740 kB
Cached:        5994028 kB
SwapCached:      50684 kB
Active:        9908900 kB
Inactive:     10783092 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:     32951124 kB
LowFree:      12014356 kB
SwapTotal:    67111528 kB
SwapFree:     66050672 kB
Dirty:            2060 kB
Writeback:           0 kB
AnonPages:    14368016 kB
Mapped:          18416 kB
Slab:           136640 kB
PageTables:      46460 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
CommitLimit:  83587088 kB
Committed_AS: 57037956 kB
VmallocTotal: 34359738367 kB
VmallocUsed:     33868 kB
VmallocChunk: 34359703231 kB
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
Hugepagesize:     2048 kB

Free space on /tmp at the end= 73272 MiB
End job on node135 at 2011-05-15 04:20:28