Thursday, May 17, 2012

Understanding CPU, I/O and memory bandwidth choices (as of May 2012)

Every year or two I have to go catch up on the latest PC hardware so I can make reasonable decisions about what gear to buy.  Here's the result of my latest inquiry into high end Intel hardware.  Thanks to William over at Puget Systems for patiently explaining it.

  • Sandybridge is the latest intel CPU architecture.  Available in i3/i5/i7/xeon and more.  All of those CPU types were around before sandybridge, so for example, i7 does not necessarily imply sandybridge.
  • Sockets: Currently Intel mostly uses the LGA1155 and LGA 2011.  i5 and i7 use LGA1155, i7 and xeon use LGA2011.  i7 and xeon motherboards have different chipsets, so generally aren't interchangeable even though they share the LGA2011 socket.
  • There are only a few LGA2011 socket i7 chips, vs. many Xeon options.
  • "Server motherboard" typically means Xeon, and dual-socket boards are more common than single-socket (6 single vs. 27 dual mobos currently on newegg right now)
  • i5 supports dual-channel memory (modules installed in pairs).  Sandybridge i7 and xeon support quad channel, which can double the memory bandwidth.
  • i5 and LGA1155 are limited to 32GB RAM.  i7 typically limited to 64GB RAM (although I see some 128GB MSI i7 mobos).  Dual-socket Xeon boards can do up to 768GB
  • ECC memory requires Xeon
  • PCIe has 3 standards: 1.0, 2.0, and 3.0.  3.0 is brand new and mostly only used for video cards right now.  1.0 does 250MB/sec per lane, 2.0 does 500MB/sec per lane, 3.0 does 1GB/sec per lane.
  • Xeon has a built-in PCI controller

Saturday, May 12, 2012

Gnome Network Manager (lucid) "apply" button greyed out

My 2wire DSL modem has a DNS server in it that I can't shut off, and when we start heavily using the network, DNS lookups get really slow or fail completely.  Lame!  Sometimes I've resorted to editing my /etc/resolv.conf by hand and then doing chattr +i to keep it from changing, but that's pretty inelegant, and sucks when I want to use wireless at work.

Turns out there's a solution in the gnome network manager gui.  Right click on the icon, then edit connections... wireless... edit the appropriate network... IPv4 settings... then change to "Automatic (DHCP) addresses only".  Then you can put, google's public DNS server, in the "DNS servers" field.

Now, when I tried that just now, it worked fine except that the "apply" button was greyed out.  I tried a bunch of things, like killing nm-applet and restarting it as root, but what finally seemed to do the trick was right clicking on the icon and unchecking "Enable networking" before doing my edits.