On 19/01/2019 02.29, Michael Jarosch wrote: > Am Freitag, den 18.01.2019, 13:43 +0000 schrieb John Davis: > >> So "ulimit -l unlimited" should set max locked mem to unlimited (both >> soft >> and hard [if root]). >> >> "ulimit -Sl unlimited" sets soft limit only. > > Thanks a lot! > What's that hard- and soft-limit for? > Or to be more concrete: Is a soft limit of any use in realtime audio? Hard limit is the limit set by administrator (actually by a parent process with right privileges), soft limit can be freely changed by a user or application, but can never exceed the hard limit. Locking too much memory or running a rogue process with real-time priority can harm whole system, for all user, up to the point a hard reboot is needed. That is why by default no real-time priorities are allowed and locking memory is very limited. System administrator may raise the hard limit, so users (or their application) can increase the soft limit, but until they do, the application are still limited to the soft limit. In case of audio purposes the soft limit (set lower than the hard limit) doesn't matter much, as it can only be reached when application actively tries to use it – uses real time processing and locks memory for that. If we want to use that, we need the soft limit be set high-enough, probably up to the hard limit, which is set to the same value. It won't affect other legitimate application and malicious app could increase the soft limit up to the hard limit anyway. For other limits, like 'number of open files' or 'amount of memory used' the soft limit setting is more useful, as users can use that to prevent applications from misbehaving – so a memory-leaking application crashes, before whole system start lagging, or a select()-call-using aplication won't break after opening 1025th file. Those affect all applications but usually are not required to be set above usual values. Jacek _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx https://lists.linuxaudio.org/listinfo/linux-audio-user
