> On Mar 12, 2018, at 3:47 PM, Song Liu <songliubrav...@fb.com> wrote:
>
>
>
>> On Mar 12, 2018, at 2:31 PM, Alexei Starovoitov <a...@fb.com> wrote:
>>
>> On 3/12/18 2:12 PM, Song Liu wrote:
>>>
>>>> On Mar 12, 2018, at 2:00 PM, Alexei Starovoitov <a...@fb.com> wrote:
>>>>
>>>> On 3/12/18 1:39 PM, Song Liu wrote:
>>>>> + page = find_get_page(vma->vm_file->f_mapping, 0);
>>>>
>>>> did you test it with config_debug_atomic_sleep ?
>>>> it should have complained...
>>>
>>> Yeah, I have CONFIG_DEBUG_ATOMIC_SLEEP=y.
>>>
>>> I think find_get_page() will not sleep. The variation find_get_page_flags()
>>> may sleep with flag FGP_CREAT.
>>
>> I see. gfp_mask == 0 and no locks. should work indeed.
>> curious how perf report looks like for heavy bpf_get_stackid() usage?
>
> I modified samples/bpf/sampleip to only call bpf_get_stackid(). The following
> is captured with bpf_get_stackid() called at 10k Hz. stressapptest is running
> with 16 threads on a system with 56 cores.
>
>
> Samples: 1M of event 'cycles:pp', Event count (approx.): 628092326243
> Overhead Command Shared Object Symbol
> + 51.61% stressapptest stressapptest [.] AdlerMemcpyC
>
> - 20.82% stressapptest [kernel.vmlinux] [k]
> queued_spin_lock_slowpath
> - queued_spin_lock_slowpath
>
> - 20.80% pcpu_freelist_pop
>
> bpf_get_stackid
>
> bpf_get_stackid_tp
>
> - 0x590c
>
> 16.12% AdlerMemcpyC
>
> 4.50% OsLayer::CpuStressWorkload
>
> + 14.36% stressapptest stressapptest [.]
> OsLayer::CpuStressWorkload
> - 8.74% stressapptest [kernel.vmlinux] [k] _raw_spin_lock
>
> - _raw_spin_lock
>
> - 8.73% bpf_get_stackid
>
> bpf_get_stackid_tp
>
> + 0x590c
>
> - 0.67% stressapptest [kernel.vmlinux] [k]
> pcpu_freelist_pop
> - pcpu_freelist_pop
>
> - 0.67% bpf_get_stackid
>
> bpf_get_stackid_tp
>
> + 0x590c
>
> Seems lock contention is the dominating overhead here. This should be the same
> for original stackmap.
>
> Song
Samples: 172K of event 'cycles:pp', Event count (approx.): 102311012653
Overhead Command Shared Object Symbol
78.84% stressapptest stressapptest [.] AdlerMemcpyC
8.78% stressapptest stressapptest [.] OsLayer::CpuStressWorkload
3.14% stressapptest [kernel.vmlinux] [k] _raw_spin_lock
2.56% stressapptest stressapptest [.] WorkerThread::FillPage
0.45% stressapptest [kernel.vmlinux] [k] perf_callchain_user
0.37% stressapptest [kernel.vmlinux] [.] native_irq_return_iret
0.31% stressapptest [kernel.vmlinux] [k] clear_page_erms
0.29% stressapptest [kernel.vmlinux] [k] pcpu_freelist_pop
0.27% stressapptest stressapptest [.] CalculateAdlerChecksum
0.25% stressapptest [kernel.vmlinux] [k] bpf_get_stackid
0.22% swapper [kernel.vmlinux] [k] poll_idle
This perf output is taken with stressapptest running on 4 cores.
bpf_get_stackid() and pcps_free_list_pop combined about 0.54% of CPU.
Song
