On Mon, May 13, 2019 at 3:02 AM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > On Sun, May 12, 2019 at 02:55:48PM -0400, tedheadster wrote: > > Christoph, > > On the same hardware (reboot with different kernel) I am getting > > _horrible_ disk I/O performance on the 5.1.1. kernel compiled on a > > 32-bit platform using HIGHMEM64G (PAE) to access 32GiB of physical > > memory. > > > > The numbers are truly terrible to copy a 16GiB file from one disk to a > > different one: > > This sounds like your storage controller only supports 32-bit DMA. > In that case any memory above that will be bounce buffered, that > is copied from one piece of memory to another, which in addition > to the copying will also create memory pressure. I have this SATA controller (using ahci kernel driver): SATA controller [0106]: Intel Corporation C610/X99 series chipset sSATA Controller [AHCI mode] [8086:8d62] (rev 05) > What storage controller do you use? Also if the CPU is 64-bit > capable you really should use a 64-bit kernel with 32-bit userspace > for a setup like that, as the VM folks do not spend any effort on > optimizing large highmem setups. I guess my request is for the VM folks to _indeed_ spend some effort optimizing large highmem setups because a 700% slowdown should be embarrassing. Who should I ask in that team about this? I do have 64-bit hardware but I regrettably have to run it in 32-bit mode with PAE support to access highmem64g memory. - Matthew
