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SubjectRe: [patch v7 02/10] add prctl task isolation prctl docs and samples
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.

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)
arg5 =

struct task_isol_quiesce_control {
__u64 flags; //with ONESHOT as the first and only possible flag for now
__u64 pad[5];
};

This way we can really do a finegrained control over each feature to quiesce.

Thanks.

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