Scott Long 96d67b46df Old PCIe implementations cannot allow a DMA transfer to cross a 4GB ... boundary. This was addressed several years ago by creating a parent tag hierarchy for the root buses that set the boundary restriction for appropriate buses and allowed child deviced to inherit it. Somewhere along the way, this restriction was turned into a case for marking the tag as a candidate for needing bounce buffers, instead of just splitting the segment along the boundary line. This flag also causes all maps associated with this tag to be non-NULL, which in turn causes bus_dmamap_sync() to take the slow path of function pointer indirection to discover that there's no bouncing work to do. The end result is a lot of pages set aside in bounce pools that will never be used, and a slow path for data buffers in nearly every DMA-capable PCIe device. For example, our workload at Netflix was spending nearly 1% of all CPU time going through this slow path. Fix this problem by being more selective about when to set the COULD_BOUNCE flag. Only set it when the boundary restriction exists and the consumer cannot do more than a single DMA segment at once. This fixes the case of dynamic buffers (mbufs, bio's) but doesn't address static buffers allocated from bus_dmamem_alloc(). That case will be addressed in the future. For those interested, this was discovered thanks to Dtrace Flame Graphs. Discussed with: jhb, kib Obtained from: Netflix, Inc. MFC after: 3 days		2014-05-20 22:43:17 +00:00
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acpica	Change default logic to CONFORM because this routine is shared	2014-03-28 02:38:14 +00:00
bios	Add missing header needed by free(9).	2012-09-30 15:42:20 +00:00
cpufreq	Do not DELAY() for P-state transition unless we want to see the result.	2013-12-10 20:25:43 +00:00
include	Add definitions for more structured extended features as well as	2014-05-16 17:45:09 +00:00
iommu	Re-implement the DMAR I/O MMU code in terms of PCI RIDs	2014-04-01 15:48:46 +00:00
isa	Remove vestiges of knowing the ISA bus, which we gave up on around 20	2014-03-19 21:03:04 +00:00
pci	Add support for managing PCI bus numbers. As with BARs and PCI-PCI bridge	2014-02-12 04:30:37 +00:00
x86	Old PCIe implementations cannot allow a DMA transfer to cross a 4GB	2014-05-20 22:43:17 +00:00
xen	Make this compile with gcc.	2014-04-05 22:43:18 +00:00