thank you for reminding me. /proc/$PID/stack shows the function call stack in kernel space,
but yesterday I thought it shows stack in user space.
I only want to understand what's the thread doing , not for a specific issue.
On 02/23/2015 06:17 AM, drago01 wrote:
On Sun, Feb 22, 2015 at 1:36 PM, Hu Jun <jhu_com@xxxxxxx> wrote:
Hi guys:
env:
[root@cloudf ~]# uname -a
Linux cloudf.fedora.com 3.18.7-100.fc20.x86_64 #1 SMP Wed Feb 11 19:01:50
UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
[root@cloudf ~]# rpm -q qemu-kvm
qemu-kvm-1.6.2-13.fc20.x86_64
I found there is a "futex" thead after creating a kvm guest by the
command:"/usr/bin/qemu-system-x86_64 -machine accel=kvm -hda
/opt/todaygoods_SLES_11_SP3_JeOS.x86_64-0.0.2.raw -vnc 192.168.0.110:6"
root@cloudf task]# ps aux | grep qemu
root 13111 0.3 2.8 546760 227340 pts/3 S+ 18:26 0:12 gdb
qemu-system-x86_64
root 14379 85.2 2.0 699004 165496 pts/3 tl 18:49 31:12
/usr/bin/qemu-system-x86_64 -machine accel=kvm -hda
/opt/todaygoods_SLES_11_SP3_JeOS.x86_64-0.0.2.raw -vnc 192.168.0.110:6
the process 14379 has three threads, I'm familiar with the two of them
except the third thread (lwp :14418)
[root@cloudf 14379]# cd /proc/14379/
[root@cloudf 14379]# cat task/14
14379/ 14416/ 14418/
[root@cloudf 14379]# cat task/14379/stack
[<ffffffff8121d1e9>] poll_schedule_timeout+0x49/0x70
[<ffffffff8121e8e4>] do_sys_poll+0x484/0x5c0
[<ffffffff8121eb24>] SyS_poll+0x74/0x110
[<ffffffff8174cfa9>] system_call_fastpath+0x12/0x17
[<ffffffffffffffff>] 0xffffffffffffffff
[root@cloudf 14379]# cat task/14416/stack
[<ffffffffa05cf92d>] kvm_arch_vcpu_ioctl_run+0xb0d/0x1280 [kvm]
[<ffffffffa05b7bb2>] kvm_vcpu_ioctl+0x292/0x5c0 [kvm]
[<ffffffff8121c710>] do_vfs_ioctl+0x2e0/0x4a0
[<ffffffff8121c951>] SyS_ioctl+0x81/0xa0
[<ffffffff8174cfa9>] system_call_fastpath+0x12/0x17
[<ffffffffffffffff>] 0xffffffffffffffff
[root@cloudf 14379]# cat task/14418/stack
[<ffffffff8110b6e0>] futex_wait_queue_me+0xd0/0x130
[<ffffffff8110b9e6>] futex_wait+0x176/0x270
[<ffffffff8110dc7e>] do_futex+0x10e/0xac0
[<ffffffff8110e6b0>] SyS_futex+0x80/0x180
[<ffffffff8174cfa9>] system_call_fastpath+0x12/0x17
[<ffffffffffffffff>] 0xffffffffffffffff
what's the "futex" thread doing when create a kvm guest ? I deeped into
the qemu code , but I failed to find where call "futex" system call.
It is unlikely that you will find any call to "futex" in the source
code of an application. It doesn't even have glibc interface.
Most of the time it is an implementation detail for something else.
For instance pthread_join is implemented using the futex system call.
But the question here is ... what is the problem that you are trying to solve?
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