On Wed, 2020-09-02 at 09:53 +0200, Thomas Gleixner wrote: > On Tue, Sep 01 2020 at 21:29, Joel Fernandes wrote: > > On Tue, Sep 01, 2020 at 10:02:10PM +0200, Thomas Gleixner wrote: > > > > > Or, are you saying users may want 'core scheduling' enabled but may > > want to > > leave out the kernel protection? > > Core scheduling per se without all the protection muck, i.e. a > relaxed > version which tries to gang schedule threads of a process on a core > if > feasible has advantages to some workloads. > Indeed! For at least two reasons, IMO:
1) what Thomas is saying already. I.e., even on a CPU which has HT but is not affected by any of the (known!) speculation issues, one may want to use Core Scheduling _as_a_feature_. For instance, for avoiding threads from different processes, or vCPUs from different VMs, sharing cores (e.g., for better managing their behavior/performance, or for improved fairness of billing/accounting). And in this case, this mechanism for protecting the kernel from the userspace on the other thread may not be necessary or interesting; 2) protection of the kernel from the other thread running in userspace may be achieved in different ways. This is one, sure. ASI will probably be another. Hence if/when we'll have both, this and ASI, it would be cool to be able to configure the system in such a way that there is only one active, to avoid paying the price of both! :-) Regards -- Dario Faggioli, Ph.D http://about.me/dario.faggioli Virtualization Software Engineer SUSE Labs, SUSE https://www.suse.com/ ------------------------------------------------------------------- <<This happens because _I_ choose it to happen!>> (Raistlin Majere)
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