Hi,
I have a two node cluster with 32 OSDs on each (one per drive). It was working fine till we spot a severe performance degradation for 4K/8K workload.
I saw one node is consuming ~5 times more cpu than other node for serving the same amount of inbound request. This is not related to disks since this is happening for smaller workload serving out of memory as well. Running perf top on both the server reveals the following.
Server A (consuming more cpu):
--------------------------------------
16.06% [kernel] [k] read_hpet
5.85% [vdso] [.] 0x0000000000000dd7
3.62% [kernel] [k] _raw_spin_lock
2.76% ceph-osd [.] crush_hash32_3
1.97% libtcmalloc.so.4.1.2 [.] operator new(unsigned long)
1.87% libc-2.19.so [.] 0x0000000000161f0b
1.34% [kernel] [k] _raw_spin_lock_irqsave
1.14% libtcmalloc.so.4.1.2 [.] operator delete(void*)
1.06% ceph-osd [.] 0x00000000007f3b26
0.99% perf [.] 0x0000000000056584
0.96% libstdc++.so.6.0.19 [.] std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string const&)
0.77% [kernel] [k] futex_wake
0.69% libstdc++.so.6.0.19 [.] 0x000000000005b644
Server B (the good one):
----------------------------
3.47% ceph-osd [.] crush_hash32_3
2.73% [kernel] [k] _raw_spin_lock
2.30% libtcmalloc.so.4.1.2 [.] operator new(unsigned long)
2.24% libc-2.19.so [.] 0x0000000000098e13
1.33% libtcmalloc.so.4.1.2 [.] operator delete(void*)
1.32% [kernel] [k] futex_wake
1.21% [kernel] [k] __schedule
1.20% libstdc++.so.6.0.19 [.] std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string const&)
1.14% ceph-osd [.] 0x00000000007f3e5f
1.13% [kernel] [k] _raw_spin_lock_irqsave
0.97% libstdc++.so.6.0.19 [.] 0x000000000005b651
0.87% [kernel] [k] futex_requeue
0.87% [kernel] [k] __copy_user_nocache
0.80% perf [.] 0x000000000005659e
0.72% [kernel] [k] __d_lookup_rcu
0.69% libpthread-2.19.so [.] pthread_mutex_trylock
0.68% [kernel] [k] futex_wake_op
0.67% libstdc++.so.6.0.19 [.] std::string::_Rep::_M_dispose(std::allocator<char> const&)
0.66% libc-2.19.so [.] vfprintf
0.62% libtcmalloc.so.4.1.2 [.] tcmalloc::ThreadCache::ReleaseToCentralCache(tcmalloc::ThreadCache::FreeList*, unsigned long, int)
0.61% ceph-osd [.] Mutex::Lock(bool)
0.57% [kernel] [k] tcp_sendmsg
So, it seems the gettimeofday + VDSO + read_hpet () is the primary reason for more cpu usage. Both the servers are identical and I couldn’t figure out why read_hpet() is consuming way more cpu on Server A. Restarting ceph-services didn’t help. Couldn’t find any abnormal message in syslog either.
My last resort was to reboot and as always that helped ☺…Now, both the nodes are behaving similarly.
Anybody has similar experience ? Am I hitting any Ubuntu (14.04.LTS , 3.13.0-32-generic) bug here ?
Any help/suggestion would be very helpful.
Thanks & Regards
Somnath
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