Hi David,
On 2015-12-11 14:21, David Holmes wrote:
On 11/12/2015 11:16 PM, Magnus Ihse Bursie wrote:
On 2015-12-03 03:11, Roger Riggs wrote:
Hi,
It would be useful to figure out the number of cpus available when in
a container.
Some comments have added to:
8140793 <https://bugs.openjdk.java.net/browse/JDK-8140793>
getAvailableProcessors may incorrectly report the number of cpus in
Docker container
But so far we haven't dug deep enough. Suggestions are welcome?
http://serverfault.com/questions/691659/count-number-of-allowed-cpus-in-a-docker-container
suggests running nproc. I'm not sure if that can be counted on to be
present, but we could certainly check for it.
I'd like to know how nproc does it so we can try to apply the same logic
in the VM for Runtime.availableProcessors. Can someone actually confirm
that it returns the number of processors available to the container?
I don't have a container at hand but running nproc under strace suggests
that it calls sched_getaffinity and counts the number of set bits in the
cpu affinity mask:
$ strace -e trace=sched_getaffinity nproc
sched_getaffinity(0, 128, {f, 0, 0, 0}) = 32
4
+++ exited with 0 +++
It would be nice if anyone with access to a system where the number of
cpus is limited in a similar manner to a docker container could run the
above command and see if it
1) returns the correct number of cpus
2) works as I think, that is, it counts the number of set bits in the
array which is the third syscall argument.
/Mikael
David
/Magnus
Roger
On 12/2/15 6:59 PM, Martin Buchholz wrote:
Not to say you shouldn't do this, but I worry that increasingly
computing
is being done in "containers" where e.g. the number of cpus is doubling
every year but only a small number are available to actually be used
by a
given process. if availableProcessors reports 1 million, what
should we
do? (no need to answer...)
On Tue, Dec 1, 2015 at 1:55 AM, Erik Joelsson
<erik.joels...@oracle.com>
wrote:
Hello,
The current heuristic for figuring out what to default set the -j
flag to
make needs some tweaking.
In JDK 9, it looks at the amount of memory and the number of cpus in
the
system. It divides memory by 1024 to get a safe number of jobs that
will
fit into memory. The lower of that number and the number of cpus is
then
picked. The number is then scaled down to about 90% of the number of
cpus
to leave some resources for other activities. It is also capped at 16.
Since we now have the build using "nice" to make sure the build isn't
bogging down the system, I see no reason to do the 90% scaling
anymore.
Also, the performance issues that forced us to cap at 16 have long
been
fixed, and even if we don't scale well beyond 16, we do still scale.
So I
propose we remove that arbitrary limitation too.
Bug: https://bugs.openjdk.java.net/browse/JDK-8144312
Webrev: http://cr.openjdk.java.net/~erikj/8144312/webrev.01/
/Erik
