Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [PATCH 07/18] x86/resctrl: Move CLOSID/RMID matching and setting to use helpers | Date | Fri, 18 Nov 2022 15:49:47 +0000 |
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On 21/10/22 13:11, James Morse wrote: > When switching tasks, the CLOSID and RMID that the new task should > use are stored in struct task_struct. For x86 the CLOSID known by resctrl, > the value in task_struct, and the value written to the CPU register are > all the same thing. > > MPAM's CPU interface has two different PARTID's one for data accesses > the other for instruction fetch. Storing resctrl's CLOSID value in > struct task_struct implies the arch code knows whether resctrl is using > CDP. > > Move the matching and setting of the struct task_struct properties > to use helpers. This allows arm64 to store the hardware format of > the register, instead of having to convert it each time. > > __rdtgroup_move_task()s use of READ_ONCE()/WRITE_ONCE() ensures torn > values aren't seen as another CPU may schedule the task being moved > while the value is being changed. MPAM has an additional corner-case > here as the PMG bits extend the PARTID space. If the scheduler sees a > new-CLOSID but old-RMID, the task will dirty an RMID that the limbo code > is not watching causing an inaccurate count. x86's RMID are independent > values, so the limbo code will still be watching the old-RMID in this > circumstance. > To avoid this, arm64 needs both the CLOSID/RMID WRITE_ONCE()d together. > Both values must be provided together. >
I think I remember something about this... Is that about having them union'd and read/written as one? (just for my own curiosity)
> Because MPAM's RMID values are not unique, the CLOSID must be provided > when matching the RMID. > > CC: Valentin Schneider <vschneid@redhat.com> > Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
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