Re: [PATCH v8 next 00/10] arm_mpam: Introduce Narrow-PARTID feature
From: Zeng Heng
Date: Wed Apr 29 2026 - 06:59:28 EST
On 2026/4/13 16:53, Zeng Heng wrote:
Background
==========
On x86, the resctrl allows creating up to num_rmids monitoring groups
under parent control group. However, ARM64 MPAM is currently limited by
the PMG (Performance Monitoring Group) count, which is typically much
smaller than the theoretical RMID limit. This creates a significant
scalability gap: users expecting fine-grained per-process or per-thread
monitoring quickly exhaust the PMG space, even when plenty of reqPARTIDs
remain available.
The Narrow-PARTID feature, defined in the ARM MPAM architecture,
addresses this by associating reqPARTIDs with intPARTIDs through a
programmable many-to-one mapping. This allows the kernel to present more
logical monitoring contexts.
Design Overview
===============
The implementation extends the RMID encoding to carry reqPARTID
information:
RMID = reqPARTID * NUM_PMG + PMG
In this patchset, a monitoring group is uniquely identified by the
combination of reqPARTID and PMG. The closid is represented by intPARTID,
which is exactly the original PARTID.
For systems with homogeneous MSCs (all supporting Narrow-PARTID), the
driver exposes the full reqPARTID range directly. For heterogeneous
systems where some MSCs lack Narrow-PARTID support, the driver utilizes
PARTIDs beyond the intPARTID range as reqPARTIDs to expand monitoring
capability. The sole exception is when any type of MSCs lack Narrow-PARTID
support, their percentage-based control mechanism prevents the use of
PARTIDs as reqPARTIDs.
Capability Improvements
=======================
--------------------------------------------------------------------------
The maximum | Sub-monitoring groups | System-wide
number of | under a control group | monitoring groups
--------------------------------------------------------------------------
Without reqPARTID | PMG | intPARTID * PMG
--------------------------------------------------------------------------
reqPARTID | |
static allocation | (reqPARTID // intPARTID) * PMG | reqPARTID * PMG
--------------------------------------------------------------------------
reqPARTID | |
dynamic allocation | (reqPARTID - intPARTID + 1) * PMG | reqPARTID * PMG
--------------------------------------------------------------------------
Note: The number of intPARTIDs can be capped via the boot parameter
mpam.intpartid_max. Under MPAM, reqPARTID count is always greater than
or equal to intPARTID count.
Thank you for your review. Please find the test report below for this
patch set.
Test Environment:
- Kernel: linux/master (commit: 6596a02b207886e9e00bb0161c7fd59fea53c081)
- Architecture: arm64
- Platform: Kunpeng 950
- MPAM Features: 256 reqPARTIDs, 32 intPARTIDs, 4 PMGs
Functional Test Example:
~~~
# dmesg | grep -i pmg
[ 11.528919] MPAM enabled with 256 reqPARTIDs, 16 intPARTIDs and 4 PMGs
# cat /proc/cmdline
<...> mpam.intpartid_max=15
# cat /sys/module/mpam/parameters/intpartid_max
15
# mount -t resctrl resctrl /sys/fs/resctrl/ -o debug
# cd /sys/fs/resctrl/
# mkdir p1
# cd p1/mon_groups/
# mkdir m{1..963}
# ls m963
cpus cpus_list mon_data mon_hw_id tasks
~~~
Able to create 964 resource groups ((256 - 15) * 4), which matches the
expected result.
MPAM KUnit Test Log:
~~~
[ 11.515338] KTAP version 1
[ 11.515340] 1..2
[ 11.515398] KTAP version 1
[ 11.515400] # Subtest: mpam_devices_test_suite
[ 11.515402] # module: mpam
[ 11.515405] 1..3
[ 11.515497] ok 1 test_mpam_reset_msc_bitmap
[ 11.515568] mpam:__props_mismatch: __props_mismatch took the min cmax_wd
[ 11.515579] mpam:__props_mismatch: cleared cpor_part
[ 11.515581] mpam:__props_mismatch: cleared mbw_part
[ 11.515592] mpam:__props_mismatch: took the min bwa_wd
[ 11.515594] mpam:__props_mismatch: __props_mismatch took the min cmax_wd
[ 11.515613] mpam:__props_mismatch: __props_mismatch took the min cmax_wd
[ 11.515658] ok 2 test_mpam_enable_merge_features
[ 11.515722] ok 3 test__props_mismatch
[ 11.515725] # mpam_devices_test_suite: pass:3 fail:0 skip:0 total:3
[ 11.515726] # Totals: pass:3 fail:0 skip:0 total:3
[ 11.515728] ok 1 mpam_devices_test_suite
[ 11.515730] KTAP version 1
[ 11.515732] # Subtest: mpam_resctrl_test_suite
[ 11.515734] # module: mpam
[ 11.515735] 1..6
[ 11.515792] ok 1 test_get_mba_granularity
[ 11.515795] KTAP version 1
[ 11.515797] # Subtest: test_mbw_max_to_percent
[ 11.515850] ok 1 pc=1, width=8, value=0x01
[ 11.515905] ok 2 pc=1, width=12, value=0x027
[ 11.515959] ok 3 pc=1, width=16, value=0x028e
[ 11.516011] ok 4 pc=25, width=8, value=0x3f
[ 11.516069] ok 5 pc=25, width=12, value=0x3ff
[ 11.516127] ok 6 pc=25, width=16, value=0x3fff
[ 11.516182] ok 7 pc=33, width=8, value=0x53
[ 11.516236] ok 8 pc=33, width=12, value=0x546
[ 11.516290] ok 9 pc=33, width=16, value=0x5479
[ 11.516345] ok 10 pc=35, width=8, value=0x58
[ 11.516401] ok 11 pc=35, width=12, value=0x598
[ 11.516456] ok 12 pc=35, width=16, value=0x5998
[ 11.516511] ok 13 pc=45, width=8, value=0x72
[ 11.516565] ok 14 pc=45, width=12, value=0x732
[ 11.516617] ok 15 pc=45, width=16, value=0x7332
[ 11.516673] ok 16 pc=50, width=8, value=0x7f
[ 11.516726] ok 17 pc=50, width=12, value=0x7ff
[ 11.516781] ok 18 pc=50, width=16, value=0x7fff
[ 11.516835] ok 19 pc=52, width=8, value=0x84
[ 11.516889] ok 20 pc=52, width=12, value=0x850
[ 11.516943] ok 21 pc=52, width=16, value=0x851d
[ 11.516997] ok 22 pc=55, width=8, value=0x8b
[ 11.517073] ok 23 pc=55, width=12, value=0x8cb
[ 11.517139] ok 24 pc=55, width=16, value=0x8ccb
[ 11.517196] ok 25 pc=58, width=8, value=0x93
[ 11.517254] ok 26 pc=58, width=12, value=0x946
[ 11.517309] ok 27 pc=58, width=16, value=0x9479
[ 11.517364] ok 28 pc=75, width=8, value=0xbf
[ 11.517418] ok 29 pc=75, width=12, value=0xbff
[ 11.517474] ok 30 pc=75, width=16, value=0xbfff
[ 11.517529] ok 31 pc=80, width=8, value=0xcb
[ 11.517583] ok 32 pc=80, width=12, value=0xccb
[ 11.517638] ok 33 pc=80, width=16, value=0xcccb
[ 11.517693] ok 34 pc=88, width=8, value=0xe0
[ 11.517750] ok 35 pc=88, width=12, value=0xe13
[ 11.517806] ok 36 pc=88, width=16, value=0xe146
[ 11.517861] ok 37 pc=95, width=8, value=0xf2
[ 11.517918] ok 38 pc=95, width=12, value=0xf32
[ 11.517972] ok 39 pc=95, width=16, value=0xf332
[ 11.518027] ok 40 pc=100, width=8, value=0xff
[ 11.518084] ok 41 pc=100, width=12, value=0xfff
[ 11.518141] ok 42 pc=100, width=16, value=0xffff
[ 11.518144] # test_mbw_max_to_percent: pass:42 fail:0 skip:0 total:42
[ 11.518146] ok 2 test_mbw_max_to_percent
[ 11.518149] KTAP version 1
[ 11.518151] # Subtest: test_percent_to_mbw_max
[ 11.518204] ok 1 pc=1, width=8, value=0x01
[ 11.518259] ok 2 pc=1, width=12, value=0x027
[ 11.518321] ok 3 pc=1, width=16, value=0x028e
[ 11.518380] ok 4 pc=25, width=8, value=0x3f
[ 11.518434] ok 5 pc=25, width=12, value=0x3ff
[ 11.518492] ok 6 pc=25, width=16, value=0x3fff
[ 11.518546] ok 7 pc=33, width=8, value=0x53
[ 11.518603] ok 8 pc=33, width=12, value=0x546
[ 11.518662] ok 9 pc=33, width=16, value=0x5479
[ 11.518718] ok 10 pc=35, width=8, value=0x58
[ 11.518776] ok 11 pc=35, width=12, value=0x598
[ 11.518832] ok 12 pc=35, width=16, value=0x5998
[ 11.518887] ok 13 pc=45, width=8, value=0x72
[ 11.518943] ok 14 pc=45, width=12, value=0x732
[ 11.519000] ok 15 pc=45, width=16, value=0x7332
[ 11.519055] ok 16 pc=50, width=8, value=0x7f
[ 11.519110] ok 17 pc=50, width=12, value=0x7ff
[ 11.519166] ok 18 pc=50, width=16, value=0x7fff
[ 11.519219] ok 19 pc=52, width=8, value=0x84
[ 11.519276] ok 20 pc=52, width=12, value=0x850
[ 11.519331] ok 21 pc=52, width=16, value=0x851d
[ 11.519387] ok 22 pc=55, width=8, value=0x8b
[ 11.519444] ok 23 pc=55, width=12, value=0x8cb
[ 11.519504] ok 24 pc=55, width=16, value=0x8ccb
[ 11.519561] ok 25 pc=58, width=8, value=0x93
[ 11.519616] ok 26 pc=58, width=12, value=0x946
[ 11.519676] ok 27 pc=58, width=16, value=0x9479
[ 11.519730] ok 28 pc=75, width=8, value=0xbf
[ 11.519785] ok 29 pc=75, width=12, value=0xbff
[ 11.519840] ok 30 pc=75, width=16, value=0xbfff
[ 11.519893] ok 31 pc=80, width=8, value=0xcb
[ 11.519946] ok 32 pc=80, width=12, value=0xccb
[ 11.519999] ok 33 pc=80, width=16, value=0xcccb
[ 11.520054] ok 34 pc=88, width=8, value=0xe0
[ 11.520106] ok 35 pc=88, width=12, value=0xe13
[ 11.520161] ok 36 pc=88, width=16, value=0xe146
[ 11.520217] ok 37 pc=95, width=8, value=0xf2
[ 11.520270] ok 38 pc=95, width=12, value=0xf32
[ 11.520323] ok 39 pc=95, width=16, value=0xf332
[ 11.520376] ok 40 pc=100, width=8, value=0xff
[ 11.520428] ok 41 pc=100, width=12, value=0xfff
[ 11.520481] ok 42 pc=100, width=16, value=0xffff
[ 11.520483] # test_percent_to_mbw_max: pass:42 fail:0 skip:0 total:42
[ 11.520485] ok 3 test_percent_to_mbw_max
[ 11.520487] KTAP version 1
[ 11.520488] # Subtest: test_mbw_max_to_percent_limits
[ 11.520540] ok 1 wd=1
[ 11.520594] ok 2 wd=2
[ 11.520647] ok 3 wd=3
[ 11.520700] ok 4 wd=4
[ 11.520752] ok 5 wd=5
[ 11.520807] ok 6 wd=6
[ 11.520858] ok 7 wd=7
[ 11.520909] ok 8 wd=8
[ 11.520962] ok 9 wd=9
[ 11.521017] ok 10 wd=10
[ 11.521078] ok 11 wd=11
[ 11.521138] ok 12 wd=12
[ 11.521193] ok 13 wd=13
[ 11.521245] ok 14 wd=14
[ 11.521296] ok 15 wd=15
[ 11.521346] ok 16 wd=16
[ 11.521348] # test_mbw_max_to_percent_limits: pass:16 fail:0 skip:0 total:16
[ 11.521350] ok 4 test_mbw_max_to_percent_limits
[ 11.521375] # test_percent_to_max_rounding: Round-up rate: 43% (18/42)
[ 11.521409] ok 5 test_percent_to_max_rounding
[ 11.521411] KTAP version 1
[ 11.521413] # Subtest: test_percent_max_roundtrip_stability
[ 11.521465] ok 1 wd=1
[ 11.521515] ok 2 wd=2
[ 11.521565] ok 3 wd=3
[ 11.521614] ok 4 wd=4
[ 11.521667] ok 5 wd=5
[ 11.521719] ok 6 wd=6
[ 11.521770] ok 7 wd=7
[ 11.521820] ok 8 wd=8
[ 11.521871] ok 9 wd=9
[ 11.521922] ok 10 wd=10
[ 11.521973] ok 11 wd=11
[ 11.522022] ok 12 wd=12
[ 11.522075] ok 13 wd=13
[ 11.522126] ok 14 wd=14
[ 11.522178] ok 15 wd=15
[ 11.522231] ok 16 wd=16
[ 11.522233] # test_percent_max_roundtrip_stability: pass:16 fail:0 skip:0 total:16
[ 11.522235] ok 6 test_percent_max_roundtrip_stability
[ 11.522237] # mpam_resctrl_test_suite: pass:6 fail:0 skip:0 total:6
[ 11.522238] # Totals: pass:118 fail:0 skip:0 total:118
[ 11.522240] ok 2 mpam_resctrl_test_suite
~~~
All 118 MPAM KUnit tests passed.
Tested-by: Zeng Heng <zengheng4@xxxxxxxxxx>
Best regards,
Zeng Heng