From 67a3e8fe90156d41cd480d3dfbb40f3bc007c262 Mon Sep 17 00:00:00 2001 From: Ross Zwisler <ross.zwisler@linux.intel.com> Date: Thu, 27 Aug 2015 13:14:20 -0600 Subject: nd_blk: change aperture mapping from WC to WB This should result in a pretty sizeable performance gain for reads. For rough comparison I did some simple read testing using PMEM to compare reads of write combining (WC) mappings vs write-back (WB). This was done on a random lab machine. PMEM reads from a write combining mapping: # dd of=/dev/null if=/dev/pmem0 bs=4096 count=100000 100000+0 records in 100000+0 records out 409600000 bytes (410 MB) copied, 9.2855 s, 44.1 MB/s PMEM reads from a write-back mapping: # dd of=/dev/null if=/dev/pmem0 bs=4096 count=1000000 1000000+0 records in 1000000+0 records out 4096000000 bytes (4.1 GB) copied, 3.44034 s, 1.2 GB/s To be able to safely support a write-back aperture I needed to add support for the "read flush" _DSM flag, as outlined in the DSM spec: http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf This flag tells the ND BLK driver that it needs to flush the cache lines associated with the aperture after the aperture is moved but before any new data is read. This ensures that any stale cache lines from the previous contents of the aperture will be discarded from the processor cache, and the new data will be read properly from the DIMM. We know that the cache lines are clean and will be discarded without any writeback because either a) the previous aperture operation was a read, and we never modified the contents of the aperture, or b) the previous aperture operation was a write and we must have written back the dirtied contents of the aperture to the DIMM before the I/O was completed. In order to add support for the "read flush" flag I needed to add a generic routine to invalidate cache lines, mmio_flush_range(). This is protected by the ARCH_HAS_MMIO_FLUSH Kconfig variable, and is currently only supported on x86. Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com> --- drivers/acpi/Kconfig | 1 + 1 file changed, 1 insertion(+) (limited to 'drivers/acpi/Kconfig') diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig index 114cf48085ab..4baeb853e0c3 100644 --- a/drivers/acpi/Kconfig +++ b/drivers/acpi/Kconfig @@ -410,6 +410,7 @@ config ACPI_NFIT tristate "ACPI NVDIMM Firmware Interface Table (NFIT)" depends on PHYS_ADDR_T_64BIT depends on BLK_DEV + depends on ARCH_HAS_MMIO_FLUSH select LIBNVDIMM help Infrastructure to probe ACPI 6 compliant platforms for -- cgit v1.2.3