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SubjectRe: [RFC PATCH 0/4] Gang scheduling in CFS

* Nikunj A Dadhania <nikunj@linux.vnet.ibm.com> wrote:

> Here some interesting perf reports from inside the guest:
>
> Baseline:
> 29.79% ebizzy [kernel.kallsyms] [k] native_flush_tlb_others
> 18.70% ebizzy libc-2.12.so [.] __GI_memcpy
> 7.23% ebizzy [kernel.kallsyms] [k] get_page_from_freelist
> 5.38% ebizzy [kernel.kallsyms] [k] __do_page_fault
> 4.50% ebizzy [kernel.kallsyms] [k] ____pagevec_lru_add
> 3.58% ebizzy [kernel.kallsyms] [k] default_send_IPI_mask_logical
> 3.26% ebizzy [kernel.kallsyms] [k] native_flush_tlb_single
> 2.82% ebizzy [kernel.kallsyms] [k] handle_pte_fault
> 2.16% ebizzy [kernel.kallsyms] [k] kunmap_atomic
> 2.10% ebizzy [kernel.kallsyms] [k] _spin_unlock_irqrestore
> 1.90% ebizzy [kernel.kallsyms] [k] down_read_trylock
> 1.65% ebizzy [kernel.kallsyms] [k] __mem_cgroup_commit_charge.clone.4
> 1.60% ebizzy [kernel.kallsyms] [k] up_read
> 1.24% ebizzy [kernel.kallsyms] [k] __alloc_pages_nodemask
>
> Gang:
> 22.53% ebizzy libc-2.12.so [.] __GI_memcpy
> 9.73% ebizzy [kernel.kallsyms] [k] ____pagevec_lru_add
> 8.22% ebizzy [kernel.kallsyms] [k] get_page_from_freelist
> 7.80% ebizzy [kernel.kallsyms] [k] default_send_IPI_mask_logical
> 7.68% ebizzy [kernel.kallsyms] [k] native_flush_tlb_others
> 6.22% ebizzy [kernel.kallsyms] [k] __do_page_fault
> 5.54% ebizzy [kernel.kallsyms] [k] native_flush_tlb_single
> 4.44% ebizzy [kernel.kallsyms] [k] _spin_unlock_irqrestore
> 2.90% ebizzy [kernel.kallsyms] [k] kunmap_atomic
> 2.78% ebizzy [kernel.kallsyms] [k] __mem_cgroup_commit_charge.clone.4
> 2.76% ebizzy [kernel.kallsyms] [k] handle_pte_fault
> 2.16% ebizzy [kernel.kallsyms] [k] __mem_cgroup_uncharge_common
> 1.59% ebizzy [kernel.kallsyms] [k] down_read_trylock
> 1.43% ebizzy [kernel.kallsyms] [k] up_read
>
> I see the main difference between both the reports is:
> native_flush_tlb_others.

So it would be important to figure out why ebizzy gets into so
many TLB flushes and why gang scheduling makes it go away.

Thanks,

Ingo


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