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SubjectRe: [PATCH] posix-timers: RCU conversion
On 03/22/2011 10:59 AM, Ben Nagy wrote:
> On Tue, Mar 22, 2011 at 12:54 PM, Eric Dumazet<eric.dumazet@gmail.com> wrote:
> > Ben Nagy reported a scalability problem with KVM/QEMU that hit very hard
> > a single spinlock (idr_lock) in posix-timers code, on its 48 core
> > machine.
>
> Hi all,
>
> Thanks a lot for all the help so far. We've tested with Eric's patch.
>
> First up, here's our version of the patch for the current ubuntu
> kernel from git:
> http://paste.ubuntu.com/583668/
>
> Here's top with 96 idle guests running:
> op - 16:47:53 up 1:09, 3 users, load average: 0.00, 0.01, 0.05
> Tasks: 499 total, 3 running, 496 sleeping, 0 stopped, 0 zombie
> Cpu(s): 1.9%us, 3.2%sy, 0.0%ni, 95.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
> Mem: 99068656k total, 13121096k used, 85947560k free, 22192k buffers
> Swap: 2438140k total, 0k used, 2438140k free, 3597860k cached
> (much better!)
>
> Start of perf top:
>
> ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> PerfTop: 10318 irqs/sec kernel:97.4% exact: 0.0% [1000Hz
> cycles], (all, 48 CPUs)
> ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> samples pcnt function DSO
> _______ _____ ___________________________
> ___________________________________________________________
>
> 95444.00 59.3% __ticket_spin_lock
> [kernel.kallsyms]
> 12937.00 8.0% native_safe_halt
> [kernel.kallsyms]
> 6149.00 3.8% kvm_get_cs_db_l_bits
> /lib/modules/2.6.38-7-server/kernel/arch/x86/kvm/kvm.ko
> 5105.00 3.2% tg_load_down
> [kernel.kallsyms]
> 5088.00 3.2% svm_vcpu_run
> /lib/modules/2.6.38-7-server/kernel/arch/x86/kvm/kvm-amd.ko
> 4807.00 3.0% kvm_set_pfn_dirty
> /lib/modules/2.6.38-7-server/kernel/arch/x86/kvm/kvm.ko
> 2855.00 1.8% ktime_get
> [kernel.kallsyms]
> 1535.00 1.0% find_busiest_group
> [kernel.kallsyms]
> 1386.00 0.9% find_next_bit
> [kernel.kallsyms]
>
>
> Start of perf report -g
> 55.26% kvm [kernel.kallsyms] [k] __ticket_spin_lock
> |
> --- __ticket_spin_lock
> |
> |--94.68%-- _raw_spin_lock
> | |
> | |--97.55%-- double_rq_lock
> | | load_balance
> | | idle_balance
> | | schedule
> | | |
> | | |--60.56%--
> schedule_hrtimeout_range_clock
> | | |
> schedule_hrtimeout_range
> | | | poll_schedule_timeout
> | | | do_select
> | | | core_sys_select
> | | | sys_select
> | | | system_call_fastpath
>
>

Looks like the posix-timer issue is completely gone, to be replaced by
the load balancer.

Copying peterz.

--
error compiling committee.c: too many arguments to function



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