linux-kernel - Re: [RFC PATCH 0/4] Gang scheduling in CFS

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Date:	Fri, 23 Dec 2011 11:36:20 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>
Cc:	Avi Kivity <avi@...hat.com>, peterz@...radead.org,
	linux-kernel@...r.kernel.org, vatsa@...ux.vnet.ibm.com,
	bharata@...ux.vnet.ibm.com
Subject: Re: [RFC PATCH 0/4] Gang scheduling in CFS


* Nikunj A Dadhania <nikunj@...ux.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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