From: Sowmini Varadhan <sowmini.varad...@oracle.com> Date: Thu, 11 Dec 2014 14:45:42 -0500
> 1. lockstat and perf report that iommu->lock is the hot-lock (in a typical > instance, I get about 21M contentions out of 27M acquisitions, 25 us > avg wait time). Even if I fix this issue (see below), I see: The real overhead is unavoidable due to the way the hypervisor access to the IOMMU is implemented in sun4v. If we had direct access to the hardware, we could avoid all of the real overhead in %99 of all IOMMU mappings, as we do for pre-sun4v systems. On sun4u systems, we never flush the IOMMU until we wrap around the end of the IOMMU arena to the beginning in order to service an allocation. Such an optimization is impossible with the hypervisor call interface in sun4v. I've known about this issue for a decade and I do not think there is anything we can really do about this. ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk _______________________________________________ E1000-devel mailing list E1000-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/e1000-devel To learn more about Intel® Ethernet, visit http://communities.intel.com/community/wired
