From: Andi Kleen <ak@xxxxxxxxxxxxxxx> On Intel systems some uncore counters are located in PCI config space. On 4S systems with many uncore events being sampled at a high frequency we can see significant overhead from the type 1 accesses: both from the IO port accesses and also from lock contention on the locks protection the IO port. This patch uses the pci_bus_force_mmconfig() interface earlier to force lockless MMCONFIG for the bus the uncore devices are residing on, which significantly lowers overhead. These busses only contain Intel on chip devices which support mmconfig. Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx> --- arch/x86/events/intel/uncore.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/x86/events/intel/uncore.c b/arch/x86/events/intel/uncore.c index 758c1aa5009d..4cc2ee3d0165 100644 --- a/arch/x86/events/intel/uncore.c +++ b/arch/x86/events/intel/uncore.c @@ -875,6 +875,12 @@ static int uncore_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id struct intel_uncore_box *box; int phys_id, pkg, ret; + /* + * Force MMCONFIG for all accesses, as we can otherwise + * have significant lock contention on the type1 IO port spinlock. + */ + pci_bus_force_mmconfig(pdev->bus); + phys_id = uncore_pcibus_to_physid(pdev->bus); if (phys_id < 0) return -ENODEV; -- 2.9.3
