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    SubjectRe: [RFC PATCH 0/4] Gang scheduling in CFS
    On 12/25/2011 12:58 PM, Avi Kivity wrote:
    > On 12/23/2011 12:36 PM, Ingo Molnar wrote:
    > > * 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.

    <snip>

    > The first part appears to be unrelated to ebizzy itself - it's the
    > kunmap_atomic() flushing ptes. It could be eliminated by switching to a
    > non-highmem kernel, or by allocating more PTEs for kmap_atomic() and
    > batching the flush.

    Um, that makes no sense. I was reading the profile as if it was a
    backtrace.

    Anyway, google says the ebizzy does a lot of large allocations - and
    presumably deallocations - to simulate a database workload, which
    explain the large number of tlb flushes.

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



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