Re: [External] [PATCH RFC 08/19] RISC-V: QoS: add resctrl interface for CBQRI controllers

[Drew Fustini <fustini@kernel.org>]

On Mon, Jan 26, 2026 at 01:02:12PM -0800, Drew Fustini wrote:
> On Mon, Jan 26, 2026 at 09:01:30PM +0800, yunhui cui wrote:
> > Hi Drew,
> > 
> > On Tue, Jan 20, 2026 at 12:15 PM Drew Fustini <fustini@kernel.org> wrote:
> > >
> > > Add interface for CBQRI controller drivers to make use of the resctrl
> > > filesystem.
> > >
> > > Co-developed-by: Adrien Ricciardi <aricciardi@baylibre.com>
> > > Signed-off-by: Adrien Ricciardi <aricciardi@baylibre.com>
> > > Signed-off-by: Drew Fustini <fustini@kernel.org>
> > > ---
> > >  arch/riscv/kernel/qos/qos_resctrl.c | 1191 +++++++++++++++++++++++++++++++++++
> > >  1 file changed, 1191 insertions(+)
> > >
> > > diff --git a/arch/riscv/kernel/qos/qos_resctrl.c b/arch/riscv/kernel/qos/qos_resctrl.c
> > > new file mode 100644
> > > index 000000000000..5e3a65342e9b
> > > --- /dev/null
> > > +++ b/arch/riscv/kernel/qos/qos_resctrl.c
[..]
> > > +       case RDT_RESOURCE_MBA:
> > > +               /* Capacity read limit operation for RCID (closid) */
> > > +               err = cbqri_bc_alloc_op(ctrl, CBQRI_CC_ALLOC_CTL_OP_READ_LIMIT, closid);
> > > +               if (err < 0) {
> > > +                       pr_err("%s(): operation failed: err = %d", __func__, err);
> > > +                       return -EIO;
> > > +               }
> > > +
> > > +               hw_dom->ctrl_val[closid] = cbqri_get_rbwb(ctrl);
> > > +
> > > +               /* Convert from bandwidth blocks to percent */
> > > +               rbwb = hw_dom->ctrl_val[closid];
> > > +               rbwb *= 100;
> > > +               percent = rbwb / ctrl->bc.nbwblks;
> > > +               if (rbwb % ctrl->bc.nbwblks)
> > > +                       percent++;
> > 
> > set: 10, get 11 ?
> 
> The intention was to handle rounding up but I can drop this increment.

Actually, this increment of one is necessary. Without it, the default
value of 80% will be displayed as 79%. And writing a value like 55% will
result in 54%.

# mount -t resctrl resctrl /sys/fs/resctrl
# cd /sys/fs/resctrl
# cat schemata
MB:0=79;1=79;2=79
L2:4=fff;5=fff
L3:3=ffff

# echo 'MB:2=55' > schemata
# cat schemata
MB:0=79;1=79;2=54
L2:4=fff;5=fff
L3:3=ffff

# echo 'MB:2=80' > schemata
# cat schemata
MB:0=79;1=79;2=79
L2:4=fff;5=fff
L3:3=ffff

Thanks,
Drew

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