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SubjectRe: [RFC PATCH 0/4] Gang scheduling in CFS
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On Wed, 21 Dec 2011 12:43:43 +0200, Avi Kivity <avi@redhat.com> wrote:
> On 12/21/2011 12:39 PM, Nikunj A Dadhania wrote:
> > On Mon, 19 Dec 2011 12:23:26 +0100, Ingo Molnar <mingo@elte.hu> wrote:
> > >
> > > * Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com> wrote:
> > >
> > > So could we please approach this from the benchmarked workload
> > > angle first? The highest improvement is in ebizzy:
> > >
> > > > ebizzy 2vm (improved 15 times, i.e. 1520%)
> > >
> > > What's behind this huge speedup? Does ebizzy use user-space
> > > spinlocks perhaps? Could we do something on the user-space side
> > > to get a similar speedup?
> > >
> > This is from the perf run on the host:
> >
> > Baseline:
> >
> > 16.22% qemu-kvm [kvm_intel] [k] free_kvm_area
> > 8.27% qemu-kvm [kvm] [k] start_apic_timer
> > 7.53% qemu-kvm [kvm] [k] kvm_put_guest_fpu
> >
> > Gang:
> >
> > 24.44% qemu-kvm [kvm_intel] [k] free_kvm_area
> > 13.42% qemu-kvm [kvm] [k] start_apic_timer
> > 9.91% qemu-kvm [kvm] [k] kvm_put_guest_fpu
> >
> > Ingo, Avi, I am not getting anything obvious from this. Any ideas?
> >

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.

Regards
Nikunj



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