Messages in this thread | | | Date | Tue, 7 Dec 2021 14:05:26 -0300 | From | Marcelo Tosatti <> | Subject | Re: [patch v7 02/10] add prctl task isolation prctl docs and samples |
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On Thu, Dec 02, 2021 at 03:29:30PM -0300, Marcelo Tosatti wrote: > On Thu, Dec 02, 2021 at 06:13:20PM +0100, Frederic Weisbecker wrote: > > On Mon, Nov 29, 2021 at 12:13:25PM -0300, Marcelo Tosatti wrote: > > > On Tue, Nov 23, 2021 at 01:36:20PM +0100, Frederic Weisbecker wrote: > > > > On Fri, Nov 12, 2021 at 09:35:33AM -0300, Marcelo Tosatti wrote: > > > > > +**PR_ISOL_CFG_SET**: > > > > > + > > > > > + Set task isolation configuration. > > > > > + The general format is:: > > > > > + > > > > > + prctl(PR_ISOL_CFG_SET, what, arg3, arg4, arg5); > > > > > + > > > > > + The 'what' argument specifies what to configure. Possible values are: > > > > > + > > > > > + - ``I_CFG_FEAT``: > > > > > + > > > > > + Set configuration of task isolation features. 'arg3' specifies > > > > > + the feature. Possible values are: > > > > > + > > > > > + - ``ISOL_F_QUIESCE``: > > > > > + > > > > > + If arg4 is QUIESCE_CONTROL, set the control structure > > > > > + for quiescing of background kernel activities, from > > > > > + the location pointed to by ``(int *)arg5``:: > > > > > + > > > > > + struct task_isol_quiesce_control { > > > > > + __u64 flags; > > > > > + __u64 quiesce_mask; > > > > > + __u64 quiesce_oneshot_mask; > > > > > + __u64 pad[5]; > > > > > + }; > > > > > + > > > > > + Where: > > > > > + > > > > > + *flags*: Additional flags (should be zero). > > > > > + > > > > > + *quiesce_mask*: A bitmask containing which kernel > > > > > + activities to quiesce. > > > > > + > > > > > + *quiesce_oneshot_mask*: A bitmask indicating which kernel > > > > > + activities should behave in oneshot mode, that is, quiescing > > > > > + will happen on return from prctl(PR_ISOL_ACTIVATE_SET), but not > > > > > + on return of subsequent system calls. The corresponding bit(s) > > > > > + must also be set at quiesce_mask. > > > > > + > > > > > + *pad*: Additional space for future enhancements. > > > > > + > > > > > + For quiesce_mask (and quiesce_oneshot_mask), possible bit sets are: > > > > > + > > > > > + - ``ISOL_F_QUIESCE_VMSTATS`` > > > > > + > > > > > + VM statistics are maintained in per-CPU counters to > > > > > + improve performance. When a CPU modifies a VM statistic, > > > > > + this modification is kept in the per-CPU counter. > > > > > + Certain activities require a global count, which > > > > > + involves requesting each CPU to flush its local counters > > > > > + to the global VM counters. > > > > > + > > > > > + This flush is implemented via a workqueue item, which > > > > > + might schedule a workqueue on isolated CPUs. > > > > > + > > > > > + To avoid this interruption, task isolation can be > > > > > + configured to, upon return from system calls, synchronize > > > > > + the per-CPU counters to global counters, thus avoiding > > > > > + the interruption. > > > > > > > > Sorry I know this is already v7 but we really don't want to screw up this interface. > > > > > > No problem. > > > > > > > What would be more simple and flexible for individual features to quiesce: > > > > > > > > arg3 = ISOL_F_QUIESCE > > > > arg4 = which feature to quiesce (eg: ISOL_F_QUIESCE_VMSTATS) > > > > > > arg4 is QUIESCE_CONTROL today so one can expand the interface > > > (by adding new commands). > > > > > > > arg5 = > > > > > > > > struct task_isol_quiesce_control { > > > > __u64 flags; //with ONESHOT as the first and only possible flag for now > > > > __u64 pad[5]; > > > > }; > > > > > > So your idea is to allow expansion at this level ? Say while adding > > > a new > > > > > > ISOL_F_QUIESCE_NEWITEM > > > > > > one can add > > > > > > struct task_isol_quiesce_control_newitem { > > > __u64 flags; > > > __u64 pad[5]; > > > }; > > > > > > And add new fields to "struct task_isol_quiesce_control_newitem". > > > > > > One downside of this suggestion is that for use-cases of the task_isol_computation.c type, > > > (see patch 2 "add prctl task isolation prctl docs and samples"), this might need > > > multiple system calls for each enable/disable cycle. Is that OK? > > > > > > See more below. > > > > > > > This way we can really do a finegrained control over each feature to quiesce. > > > > > > With the patchset above, one can add new values to arg4 > > > (at the same level of QUIESCE_CONTROL). Your suggestion does not save > > > room for that. > > > > > > One could add new values to the same space of I_CFG_FEAT: > > > > > > prctl(PR_ISOL_CFG_SET, I_CFG_FEAT_xxx, ...); > > > > > > But that sounds awkward. > > > > > > Or change the current ioctl to: > > > > > > prctl(PR_ISOL_CFG, I_CFG_FEAT_CONTROL, ...); > > > > > > Which makes it less awkward. > > > > > > What do you say? > > > > > > --- > > > > > > And then, what about keeping the bitmaps with enabled/one-shot mode > > > per feature per bit (to avoid multiple system calls) > > > but having (in the future) additional per-quiesce instance commands ? > > > > Ok got your points. > > > > I guess we can then simply rename ISOL_F_QUIESCE to ISOL_F_QUIESCE_MULTIPLE > > for simple all-in-one configuration. Then if the need ever arise in the future, > > we can always add ISOL_F_QUIESCE (or ISOL_F_QUIESCE_ONE) to do finegrained > > control over a single quiescing feature. > > > > Does that sound ok? > > Yep, it does, will change that.
Actually, after performing some of the changes, it turns out that just adding ISOL_F_QUIESCE_ONE to configure individual features, and keeping the current ISOL_F_QUIESCE works just as well.
Fixed the other issues you raised, and added documentation about the possibility of ISOL_F_QUIESCE_ONE.
Will resend.
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