On 7/27/21 7:42 AM, Frederic Weisbecker wrote:
On Tue, Jul 20, 2021 at 10:18:31AM -0400, Waiman Long wrote:
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=TBD
commit 994fb794cb252edd124a46ca0994e37a4726a100
Author: Waiman Long <longman@xxxxxxxxxx>
Date: Sat, 19 Jun 2021 13:28:19 -0400
cgroup/cpuset: Add a new isolated cpus.partition type
Cpuset v1 uses the sched_load_balance control file to determine if load
balancing should be enabled. Cpuset v2 gets rid of sched_load_balance
as its use may require disabling load balancing at cgroup root.
For workloads that require very low latency like DPDK, the latency
jitters caused by periodic load balancing may exceed the desired
latency limit.
When cpuset v2 is in use, the only way to avoid this latency cost is to
use the "isolcpus=" kernel boot option to isolate a set of CPUs. After
the kernel boot, however, there is no way to add or remove CPUs from
this isolated set. For workloads that are more dynamic in nature, that
means users have to provision enough CPUs for the worst case situation
resulting in excess idle CPUs.
To address this issue for cpuset v2, a new cpuset.cpus.partition type
"isolated" is added which allows the creation of a cpuset partition
without load balancing. This will allow system administrators to
dynamically adjust the size of isolated partition to the current need
of the workload without rebooting the system.
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Nice! And while we are adding a new ABI, can we take advantage of that and
add a specific semantic that if a new isolated partition matches a subset of
"isolcpus=", it automatically maps to it. This means that any further
modification to that isolated partition will also modify the associated
isolcpus= subset.
Or to summarize, when we create a new isolated partition, remove the associated
CPUs from isolcpus= ?
We can certainly do that as a follow-on. Another idea that I have been
thinking about is to automatically generating a isolated partition under
root to match the given isolcpus parameter when the v2 filesystem is
mounted. That needs more experimentation and testing to verify that it
can work.
Cheers,
Longman
