On Sun, Nov 29, 2015 at 5:37 PM, Nir Soffer <nsoffer@redhat.com> wrote:
On Sun, Nov 29, 2015 at 10:37 AM, Yaniv Kaul <ykaul@redhat.com> wrote:
On Fri, Nov 27, 2015 at 6:55 PM, Francesco Romani <fromani@redhat.com> wrote:
Using taskset, the ip command now takes a little longer to complete.
Since we always use the same set of CPUs, I assume using a mask (for 0 &
just use 0x3, as the man suggests) might be a tiny of a fraction faster to execute taskset with, instead of the need to translate the numeric CPU
1, list.
Creating the string "0-<last cpu index>" is one line in vdsm. The code handling this in taskset is written in C, so the parsing time is practically zero. Even if it was non-zero, this code run once when we run a child process, so the cost is insignificant.
I think it's easier to just to have it as a mask in a config item somewhere, without need to create it or parse it anywhere. For us and for the user.
However, the real concern is making sure CPUs 0 & 1 are not really too busy with stuff (including interrupt handling, etc.)
This code is used when we run a child process, to allow the child process to run on all cpus (in this case, cpu 0 and cpu 1). So I think there is no concern here.
Vdsm itself is running by default on cpu 1, which should be less busy then cpu 0.
I assume those are cores, which probably in a multi-socket will be in the first socket only. There's a good chance that the FC and or network/cards will also bind their interrupts to core0 & core 1 (check /proc/interrupts) on the same socket.
From my poor laptop (1s, 4c): 42: 1487104 9329 4042 3598 IR-PCI-MSI 512000-edge 0000:00:1f.2
(my SATA controller) 43: 14664923 34 18 13 IR-PCI-MSI 327680-edge xhci_hcd (my dock station connector) 45: 6754579 4437 2501 2419 IR-PCI-MSI 32768-edge i915 (GPU) 47: 187409 11627 1235 1259 IR-PCI-MSI 2097152-edge iwlwifi (NIC, wifi) Y.
The user can modify this configuration on the host, I guess we need to expose this on the engine side (cluster setting?).
Also if vdsm is pinned to certain cpu, should user get a warning trying to pin a vm to this cpu?
Michal, what do you think?
Nir