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)?
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