On Wed, Jul 18, 2012 at 02:50:14PM -0400, Konrad Rzeszutek Wilk wrote:
> On Wed, Jul 18, 2012 at 12:36:43PM -0500, W. Michael Petullo wrote:
> > >>>> We have seen a significant reduction in performance in our research 
> > >>>> DomU
> > >>>> OS kernel when running on Fedora 16 with Linux 3.4.2 vs. 3.3.7. We run
> > >>> a series of benchmarks which are DomU-kernel-space-CPU-heavy; many of
> > >>>> these run 10x slower when using the 3.4.2 Linux kernel as Dom0.
> > 
> > >>>> This is a little surprising---we've been tracking the Fedora kernels 
> > >>>> for
> > >>>> a long time with no problem like this. Did anyone else notice any 
> > >>>> changes?
> > 
> > >>> Just to verify.. both the 3.3.7 and 3.4.2 Linux kernel are 'release' 
> > >>> builds? 
> > >>> and not debug-versions from rawhide? 
> > 
> > >> Yes, they are the Fedora 16 release builds.
> >  
> > > The commits that went in (3.4) were:
> > > 
> > > 1fd1443 xen/Kconfig: fix Kconfig layout
> > > 76a8df7 xen/pci: don't use PCI BIOS service for configuration space 
> > > accesses
> > > b7e5ffe xen/pte: Fix crashes when trying to see non-existent 
> > > PGD/PMD/PUD/PTEs
> > > 558daa2 xen/apic: Return the APIC ID (and version) for CPU 0.
> > > a7a97c6 drivers/video/xen-fbfront.c: add missing cleanup code
> > > 7eb7ce4 xen: correctly check for pending events when restoring irq flags
> > > b930fe5 xen/acpi: Workaround broken BIOSes exporting non-existing 
> > > C-states.
> > > cf405ae xen/smp: Fix crash when booting with ACPI hotplug CPUs.
> > > 521394e xen: use the pirq number to check the pirq_eoi_map
> > > df88b2d xen/enlighten: Disable MWAIT_LEAF so that acpi-pad won't be 
> > > loaded.
> > > cd74257 x86, acpi: Call acpi_enter_sleep_state via an asmlinkage C 
> > > function from assembler
> > > 2a14e54 ACPI: Convert wake_sleep_flags to a value instead of function
> > > 3d81acb Revert "xen/p2m: m2p_find_override: use list_for_each_entry_safe"
> > > 186bab1 xen/resume: Fix compile warnings.
> > > 3066616 xen/xenbus: Add quirk to deal with misconfigured backends.
> > > a71e23d xen/blkback: Fix warning error.
> > > b960d6c xen/p2m: m2p_find_override: use list_for_each_entry_safe
> > > e8e937b xen/gntdev: do not set VM_PFNMAP
> > > 6b5e7d9 xen/grant-table: add error-handling code on failure of 
> > > gnttab_resume
> > > f09d843 xen/pcifront: avoid pci_frontend_enable_msix() falsely returning 
> > > success
> > > 0ee46ec xen/pciback: fix XEN_PCI_OP_enable_msix result
> > > e8c9e78 xen/smp: Remove unnecessary call to smp_processor_id()
> > > 2531d64 xen/x86: Workaround 'x86/ioapic: Add register level checks to 
> > > detect bogus io-apic entries'
> > > e95ae5a xen: only check xen_platform_pci_unplug if hvm
> > > 136d249 x86/ioapic: Add io_apic_ops driver layer to allow interception
> > > 3389bb8 xen/blkback: Make optional features be really optional.
> > > 4dae767 xen/blkback: Squash the discard support for 'file' and 'phy' type.
> > > df7a3ee xen/acpi: Fix Kconfig dependency on CPU_FREQ
> > > f132c5b Fix full_name_hash() behaviour when length is a multiple of 8
> > > b9136d2 xen: initialize platform-pci even if xen_emul_unplug=never
> > > 106b443 xen/smp: Fix bringup bug in AP code.
> > > 27257fc xen/acpi: Remove the WARN's as they just create noise.
> > > 8e6f7c2 xen/tmem: cleanup
> > > 9846ff1 xen: support pirq_eoi_map
> > > 102b208 xen/acpi-processor: Do not depend on CPU frequency scaling 
> > > drivers.
> > > 48cdd82 xen/cpufreq: Disable the cpu frequency scaling drivers from 
> > > loading.
> > > 448c8b1 provide disable_cpufreq() function to disable the API.
> > > 3467811 xen-blkfront: make blkif_io_lock spinlock per-device
> > > dad5cf6 xen/blkfront: don't put bdev right after getting it
> > > 34ae2e4 xen-blkfront: use bitmap_set() and bitmap_clear()
> > > b2167ba xen/blkback: Enable blkback on HVM guests
> > > 4f14faa xen/blkback: use grant-table.c hypercall wrappers
> > > 4bc25af xen kconfig: relax INPUT_XEN_KBDDEV_FRONTEND deps
> > > a7b422c provide disable_cpufreq() function to disable the API.
> > > 59a5680 xen/acpi-processor: C and P-state driver that uploads said data 
> > > to hypervisor.
> > > ead1d01 xen: constify all instances of "struct attribute_group"
> > > 42c46e6 xen/xenbus: ignore console/0
> > > cf8e019 hvc_xen: introduce HVC_XEN_FRONTEND
> > > 02e19f9 hvc_xen: implement multiconsole support
> > > eb5ef07 hvc_xen: support PV on HVM consoles
> > > bd0d5aa xenbus: don't free other end details too early
> > > a1f37788 tboot: Add return values for tboot_sleep
> > > 09f98a8 x86, acpi, tboot: Have a ACPI os prepare sleep instead of calling 
> > > tboot_sleep.
> > > 73c154c xen/enlighten: Expose MWAIT and MWAIT_LEAF if hypervisor OKs it.
> > > cc7335b xen/setup/pm/acpi: Remove the call to boot_option_idle_override.
> > > 5ac0800 xenbus: address compiler warnings
> > > 1160831 xen/pciback: Support pci_reset_function, aka FLR or D3 support.
> > > 6fbf9e7 PCI: Introduce __pci_reset_function_locked to be used when 
> > > holding device_lock.
> > > cf66f9d xen/netfront: add netconsole support.
> > > f3ff924 Remove useless get_driver()/put_driver() calls
> > > 2113f46 xen: use this_cpu_xxx replace percpu_xxx funcs
> > > cd9db80 xen/pciback: Support pci_reset_function, aka FLR or D3 support.
> > > a96d627 pci: Introduce __pci_reset_function_locked to be used when 
> > > holding device_lock.
> > > 8605c68 xen: Utilize the restore_msi_irqs hook.
> > 
> > I'm having trouble with the Dom0 performance of this kernel too (vs. its
> > effect on DomU performance). I submitted a bug with a reproducible
> > test case:
> > 
> > https://bugzilla.redhat.com/show_bug.cgi?id=841330
> 
> OK, did you try any of the options I've asked for (see earlier part of the
> thread)?

And you are running an AMD CPU. I think you are hitting an Xen power affecting
bug. See in 3.4 the driver that uploads power mananagement data to the 
hypervisor
is now enabled - which means it exposes some power management functionality
in the hypervisor that v3.3 did not activate. Hence I want you try to run
the hypervisor at performance mode to double check.


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