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The PCI spec recommends devices use additional alignment for MSI-X data structures to allow software to map them to separate processor pages. One advantage of doing this is that we can emulate those data structures without a significant performance impact to the operation of the device. Some devices fail to implement that suggestion and assigned device performance suffers. One such case of this is a Mellanox MT27500 series, ConnectX-3 VF, where the MSI-X vector table and PBA are aligned on separate 4K pages. If PBA emulation is enabled, performance suffers. It's not clear how much value we get from PBA emulation, but the solution here is to only lazily enable the emulated PBA when a masked MSI-X vector fires. We then attempt to more aggresively disable the PBA memory region any time a vector is unmasked. The expectation is then that a typical VM will run entirely with PBA emulation disabled, and only when used is that emulation re-enabled. Reported-by: Shyam Kaushik <shyam.kaushik@gmail.com> Tested-by: Shyam Kaushik <shyam.kaushik@gmail.com> Signed-off-by: Alex Williamson <alex.williamson@redhat.com> |
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| .. | ||
| calxeda-xgmac.c | ||
| common.c | ||
| Makefile.objs | ||
| pci-quirks.c | ||
| pci.c | ||
| pci.h | ||
| platform.c | ||