Linux Mint 16: Skype uses 100% of CPU core

Question

I use Linux Mint 16 Petra 64bit Cinnamon. When I install Skype (either from repo, or directly from Microsoft) it soon starts using 100% of 1 CPU Core, doubling power consumption of my system.

I tried removing the ~/.skype folder and logging with different account.

I tried removing the skype from repositories and install it directly from Microsoft.

Is there anything I can do to troubleshoot and fix this problem?

I can't reproduce this problem with older Mints, nor with Ubuntu Saucy and Raring.

The doesn't manifest itself, if I launch skype and never log in (keep skype displaying the login screen). But if the skype was logged in before and had the high CPU consumption - clicking "Sign Out" doesn't help the problem (besides even if it did, there is little point in using skype without logging in)

---

Following the advise of @slm I can include the strace output. It seems that Skype is busy doing poll syscall... I thought that polling for resource introduces processor idling, not 100% usage.

 strace -c skype
[ Process PID=31614 runs in 32 bit mode. ]

% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
  0.00    0.000000           0         1           execve
------ ----------- ----------- --------- --------- ----------------
100.00    0.000000                     1           total
System call usage summary for 32 bit mode:
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 96.95   45.349256         493     92056           poll
  1.26    0.588104           2    279026           clock_gettime
  0.99    0.462877           3    183996    182979 recv
  0.33    0.156517           2     79850       468 stat64
  0.30    0.138574           2     79740           gettimeofday
  0.10    0.047275          45      1040       174 futex
  0.04    0.020046        1671        12           nanosleep
  0.01    0.003025           4       792           writev
  0.00    0.002037           2       871           write
  0.00    0.001928           3       692       143 read
  0.00    0.001482           2       944       561 open
  0.00    0.000591           2       333       238 access
  0.00    0.000584           1       466           mmap2
  0.00    0.000577           1       421           madvise
  0.00    0.000485           1       431           close
  0.00    0.000462           4       120           munmap
  0.00    0.000378           3       115           mprotect
  0.00    0.000372           4        86           fstatfs64
  0.00    0.000269           1       263           fstat64
  0.00    0.000175           3        66        29 recvmsg
  0.00    0.000113           1       121           time
  0.00    0.000108           1       113         5 lstat64
  0.00    0.000082           3        29           getdents64
  0.00    0.000056           2        30           fadvise64_64
  0.00    0.000047           3        15           openat
  0.00    0.000046          15         3           shmdt
  0.00    0.000045           2        24           sendmsg
  0.00    0.000038           2        22           clone
  0.00    0.000037           1        33           socket
  0.00    0.000032           2        13           _llseek
  0.00    0.000032          11         3           shmat
  0.00    0.000032          11         3           shmget
  0.00    0.000031           1        29           brk
  0.00    0.000027           5         6           shmctl
  0.00    0.000015           2         9           send
  0.00    0.000013           0        27           fcntl64
  0.00    0.000011           2         6         2 connect
  0.00    0.000007           2         3           readlink
  0.00    0.000007           1        13           rt_sigaction
  0.00    0.000005           1         4           geteuid32
  0.00    0.000005           1         4           getsockname
  0.00    0.000003           0        10           uname
  0.00    0.000003           3         1           eventfd2
  0.00    0.000003           3         1           pipe2
  0.00    0.000002           2         1           set_tid_address
  0.00    0.000002           2         1           getpeername
  0.00    0.000001           1         2           rt_sigprocmask
  0.00    0.000001           1         2           getrlimit
  0.00    0.000001           1         2           clock_getres
  0.00    0.000001           1         1           set_robust_list
  0.00    0.000000           0         2           unlink
  0.00    0.000000           0         2           chmod
  0.00    0.000000           0         3         3 mkdir
  0.00    0.000000           0         1           pipe
  0.00    0.000000           0        22           ioctl
  0.00    0.000000           0         1           umask
  0.00    0.000000           0         4           statfs
  0.00    0.000000           0         4           fstatfs
  0.00    0.000000           0         2           flock
  0.00    0.000000           0         3           getuid32
  0.00    0.000000           0         1           getgid32
  0.00    0.000000           0         1           getegid32
  0.00    0.000000           0         1           getresuid32
  0.00    0.000000           0         1           getresgid32
  0.00    0.000000           0         2           gettid
  0.00    0.000000           0         1           sched_getaffinity
  0.00    0.000000           0         1           set_thread_area
  0.00    0.000000           0         4         1 bind
  0.00    0.000000           0         1           listen
  0.00    0.000000           0         2           sendto
  0.00    0.000000           0         1           shutdown
------ ----------- ----------- --------- --------- ----------------
100.00   46.775820                721911    184603 total

When I attach strace to running skype with sudo strace -p $(pgrep skype) I get tons of the following entries:

clock_gettime(CLOCK_MONOTONIC, {7553, 920730509}) = 0
recv(6, 0xf967e5a8, 4096, 0)            = -1 EAGAIN (Resource temporarily unavailable)
clock_gettime(CLOCK_MONOTONIC, {7553, 920937548}) = 0
poll([{fd=3, events=POLLIN}, {fd=7, events=POLLIN}, {fd=6, events=POLLIN}, {fd=9, events=POLLIN}, {fd=12, events=POLLIN}, {fd=28, events=POLLIN}], 6, 0) = 0 (Timeout)
recv(6, 0xf967e5a8, 4096, 0)            = -1 EAGAIN (Resource temporarily unavailable)
clock_gettime(CLOCK_MONOTONIC, {7553, 921039735}) = 0
recv(6, 0xf967e5a8, 4096, 0)            = -1 EAGAIN (Resource temporarily unavailable)
clock_gettime(CLOCK_MONOTONIC, {7553, 921089170}) = 0
poll([{fd=3, events=POLLIN}, {fd=7, events=POLLIN}, {fd=6, events=POLLIN}, {fd=9, events=POLLIN}, {fd=12, events=POLLIN}, {fd=28, events=POLLIN}], 6, 0) = 0 (Timeout)

Answer 1

strace profile

You could try debugging it further using strace to see what system calls skype is making that are causing the surge in resources. This will show you what system calls skype is stuck in.

Example

$ strace -c ls
afile1  afile2  afile3  afile4  afile5
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
  0.00    0.000000           0         8           read
  0.00    0.000000           0         1           write
  0.00    0.000000           0        10           open
  0.00    0.000000           0        13           close
  0.00    0.000000           0         1           stat
  0.00    0.000000           0        11           fstat
  0.00    0.000000           0        27           mmap
  0.00    0.000000           0        18           mprotect
  0.00    0.000000           0         2           munmap
  0.00    0.000000           0         3           brk
  0.00    0.000000           0         2           rt_sigaction
  0.00    0.000000           0         1           rt_sigprocmask
  0.00    0.000000           0         2           ioctl
  0.00    0.000000           0         1         1 access
  0.00    0.000000           0         1           execve
  0.00    0.000000           0         2           getdents
  0.00    0.000000           0         1           getrlimit
  0.00    0.000000           0         2           statfs
  0.00    0.000000           0         1           arch_prctl
  0.00    0.000000           0         1           set_tid_address
  0.00    0.000000           0         1           openat
  0.00    0.000000           0         1           set_robust_list
------ ----------- ----------- --------- --------- ----------------
100.00    0.000000                   110         1 total

top & htop

You can also monitor skype using a tool such as top or htop to see what the processes is doing overall.

   

strace - attaching to a running process

You can also use strace to attach to already running processes. This allows you to attach after they've started to misbehave.

Example

Say we want to attach to our already running htop process from above.

$ pgrep htop
32495

This is htop's PID - process ID. You can use these to connect strace.

$ strace -p 32495 |& head -10
Process 32495 attached
select(1, [0], NULL, NULL, {0, 729724}) = 0 (Timeout)
open("/proc/meminfo", O_RDONLY)         = 3
fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f685faf1000
read(3, "MemTotal:        7969128 kB\nMemF"..., 1024) = 1024
read(3, "e:        0\nHugePages_Rsvd:     "..., 1024) = 146
read(3, "", 1024)                       = 0
close(3)                                = 0
munmap(0x7f685faf1000, 4096)            = 0
...
...

---

UPDATE #1 - debugging the poll() syscalls

The strace the OP provided show a high level of poll() system calls. You can find out what these are via man poll.

   poll, ppoll - wait for some event on a file descriptor

So Skype is waiting on a file descriptor, but in this case it isn't necessarily a file, it may be, but probably it's waiting on a network resource that is wrapped in a file descriptor.

Example

To show this a little better here's an example. Say we were downloading a 100MB file like this using wget.

$ wget -O /dev/null http://speedtest.wdc01.softlayer.com/downloads/test100.zip

We could then see what file descriptors were in use using the command lsof -c wget.

$ lsof -c wget
COMMAND   PID USER   FD   TYPE  DEVICE  SIZE/OFF    NODE NAME
wget    11531 saml  cwd    DIR   253,2      4096 7340394 /home/saml/media/mp3s/kids_music
wget    11531 saml  rtd    DIR   253,1      4096       2 /
wget    11531 saml  txt    REG   253,1    421712  531380 /usr/bin/wget
wget    11531 saml  mem    REG   253,1    310576  544452 /usr/lib64/libgssapi_krb5.so.2.2
...
...
wget    11531 saml  mem    REG   253,1     62368  528212 /usr/lib64/libnss_files-2.17.so
wget    11531 saml  mem    REG   253,1 106055264  803764 /usr/lib/locale/locale-archive
wget    11531 saml  mem    REG   253,1     26254  660143 /usr/lib64/gconv/gconv-modules.cache
wget    11531 saml    0u   CHR   136,2       0t0       5 /dev/pts/2
wget    11531 saml    1u   CHR   136,2       0t0       5 /dev/pts/2
wget    11531 saml    2u   CHR   136,2       0t0       5 /dev/pts/2
wget    11531 saml    3w   CHR     1,3       0t0    1028 /dev/null
wget    11531 saml    4u  IPv4 1543927       0t0     TCP greeneggs.bubba.net:55907->speedtest.wdc01.softlayer.com:htt

Notice the last line, that's a file descriptor for our connection to softlayer.com. So the network connection is also treated as a a poll() to via a file descriptor. You can do the same and confirm using a command such as:

$ lsof -c skype

Answer 2

After re-installation of the whole system in seemingly the same way as the affected system was installed, the problem never re-appeared.

(And who says that you don't have to format the hard drive to solve solve problems under Linux? ;-) )