On 10.11.21 17:10, Marcelo Tosatti wrote: > On Wed, Nov 10, 2021 at 03:21:54PM +0000, Moessbauer, Felix wrote: >> >> >>> -----Original Message----- >>> From: Michal Koutný <mkoutny@xxxxxxxx> >>> Sent: Wednesday, November 10, 2021 2:57 PM >>> To: Moessbauer, Felix (T RDA IOT SES-DE) <felix.moessbauer@xxxxxxxxxxx> >>> Cc: longman@xxxxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx; >>> cgroups@xxxxxxxxxxxxxxx; corbet@xxxxxxx; frederic@xxxxxxxxxx; guro@xxxxxx; >>> hannes@xxxxxxxxxxx; juri.lelli@xxxxxxxxxx; linux-doc@xxxxxxxxxxxxxxx; linux- >>> kernel@xxxxxxxxxxxxxxx; linux-kselftest@xxxxxxxxxxxxxxx; >>> lizefan.x@xxxxxxxxxxxxx; mtosatti@xxxxxxxxxx; pauld@xxxxxxxxxx; >>> peterz@xxxxxxxxxxxxx; shuah@xxxxxxxxxx; tj@xxxxxxxxxx; Kiszka, Jan (T RDA >>> IOT) <jan.kiszka@xxxxxxxxxxx>; Schild, Henning (T RDA IOT SES-DE) >>> <henning.schild@xxxxxxxxxxx> >>> Subject: Re: [PATCH v8 0/6] cgroup/cpuset: Add new cpuset partition type & >>> empty effecitve cpus >>> >>> Hello. >>> >>> On Wed, Nov 10, 2021 at 12:13:57PM +0100, Felix Moessbauer >>> <felix.moessbauer@xxxxxxxxxxx> wrote: >>>> However, I was not able to see any latency improvements when using >>>> cpuset.cpus.partition=isolated. >>> >>> Interesting. What was the baseline against which you compared it (isolcpus, no >>> cpusets,...)? >> >> For this test, I just compared both settings cpuset.cpus.partition=isolated|root. >> There, I did not see a significant difference (but I know, RT tuning depends on a ton of things). >> >>> >>>> The test was performed with jitterdebugger on CPUs 1-3 and the following >>> cmdline: >>>> rcu_nocbs=1-4 nohz_full=1-4 irqaffinity=0,5-6,11 intel_pstate=disable >>>> On the other cpus, stress-ng was executed to generate load. >>>> [...] >>> >>>> This requires cgroup.type=threaded on both cgroups and changes to the >>>> application (threads have to be born in non-rt group and moved to rt-group). >>> >>> But even with isolcpus the application would need to set affinity of threads to >>> the selected CPUs (cf cgroup migrating). Do I miss anything? >> >> Yes, that's true. But there are two differences (given that you use isolcpus): >> 1. the application only has to set the affinity for rt threads. >> Threads that do not explicitly set the affinity are automatically excluded from the isolated cores. >> Even common rt test applications like jitterdebugger do not pin their non-rt threads. >> 2. Threads can be started on non-rt CPUs and then bound to a specific rt CPU. >> This binding can be specified before thread creation via pthread_create. >> By that, you can make sure that at no point in time a thread has a "forbidden" CPU in its affinities. >> >> With cgroup2, you cannot guarantee the second aspect, as thread creation and moving to a cgroup is not an atomic operation. >> Also - please correct me if I'm wrong - you first have to create a thread before moving it into a group. >> At creation time, you cannot set the final affinity mask (as you create it in the non-rt group and there the CPU is not in the cpuset.cpus). >> Once you move the thread to the rt cgroup, it has a default mask and by that can be executed on other rt cores. > > man clone3: > > CLONE_NEWCGROUP (since Linux 4.6) > Create the process in a new cgroup namespace. If this flag is not set, then (as with fork(2)) the > process is created in the same cgroup namespaces as the calling process. > > For further information on cgroup namespaces, see cgroup_namespaces(7). > > Only a privileged process (CAP_SYS_ADMIN) can employ CLONE_NEWCGROUP. > Is there pthread_attr_setcgroup_np()? Jan -- Siemens AG, T RDA IOT Corporate Competence Center Embedded Linux
