PQOS tool measures 0.0 for MBL and MBR with MLC on AMD systems

[babumoger]

When using the pqos tool to monitor memory bandwidth, both MBL (Memory Bandwidth Local) and MBR (Memory Bandwidth Remote) are reported as 0.0, even while a memory-intensive workload such as MLC is running.

Steps to Reproduce
Boot an AMD system with Linux kernel v6.18 or later.
Ensure the system supports the mbm_event monitoring mode and that it is enabled.
Run a memory bandwidth workload (for example, MLC).
In parallel, run the pqos monitoring command:
#sudo pqos -m all:[0-191]

Example output:

CORE IPC MISSES LLC[KB] MBL[MB/s] MBR[MB/s]
0-191 0.01 109937k 385600.0 0.0 0.0

Observed Behavior

The MBL and MBR counters remain at 0.0 despite ongoing memory traffic generated by MLC.

Additional Information

The issue is observed when the system is operating in mbm_event mode and the number of available MBM counters (num_mbm_cntrs) is limited to 32.
#cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
[mbm_event]
default

#cat /sys/fs/resctrl/info/L3_MON/num_mbm_cntrs
0=32;1=32

This issue appears to be specific to AMD systems that support and have enabled the mbm_event assignment mode.

[rkanagar]

Hi @babumoger ,
Are you using latest intel-cmt-cat master? Can you please provide the full output of the command using msr interface and os interface? The default is not OS interface now.

sudo pqos --iface=msr -m all:[0-191] -VVV
sudo pqos --iface=os -m all:[0-191] -VVV

[babumoger]

Hi, It is using the OS interface. Here are the details. sudo pqos --version PQoS Tool version: 7.1.0 Selected interface: OS WARN: Could not obtain ERDT table PQoS Library version: 7.1.0 I will update it to latest version soon. thanks

…

On 7/27/2026 5:32 PM, rkanagar wrote: *rkanagar* left a comment (intel/intel-cmt-cat#311) <https://github.com/ intel/intel-cmt-cat#311#issuecomment-5097514514> Hi @babumoger <https://github.com/babumoger> , Are you using latest intel-cmt-cat master? Can you please provide the full output of the command using msr interface and os interface? The default is not OS interface now. — Reply to this email directly, view it on GitHub <https://github.com/ intel/intel-cmt-cat#311? email_source=notifications&email_token=AIFLFVBYT3Q474MVTKVOCET5G7J6BA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTKMBZG42TCNBVGE2KM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLDGN5XXIZLSL5RWY2LDNM#issuecomment-5097514514>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AIFLFVBEUOQFEENRE7M3A6L5G7J6BAVCNFSNUABEKJSXA33TNF2G64TZHMZDQMJUGY2TKOB3JFZXG5LFHM2DSOJRGM2DCMBRG2QXMAQ>. Triage notifications, keep track of coding agent tasks and review pull requests on the go with GitHub Mobile for iOS <https://github.com/ notifications/mobile/ios/ AIFLFVCKFH6LL3FLH22HXXT5G7J6BA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTKMBZG42TCNBVGE2KM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJKTGN5XXIZLSL5UW64Y> and Android <https://github.com/notifications/mobile/android/AIFLFVA46C4SCJGCQ74BRI35G7J6BA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTKMBZG42TCNBVGE2KM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLTGN5XXIZLSL5QW4ZDSN5UWI>. Download it today! You are receiving this because you were mentioned.Message ID: <intel/ ***@***.***>

[rstorozh]

Hi Babu,

In addition to info requested by Raghavan, please also provide the output of the configuration:
$ sudo pqos/pqos -d
and
$ sudo pqos/pqos -D

And monitoring:
$ sudo pqos/pqos --iface=OS pqos/pqos -m mbt:0-191

Probably your HW configuration doesn't support remote memory. In this case only MBT count.

[babumoger]

#sudo pqos -d Selected interface: OS WARN: Could not obtain ERDT table OS capabilities (Linux kernel 7.2.0-rc3+) Monitoring Cache Monitoring Technology (CMT) events: LLC Occupancy (LLC) I/O RDT: unsupported Memory Bandwidth Monitoring (MBM) events: Local Memory Bandwidth (LMEM) I/O RDT: unsupported Total Memory Bandwidth (TMEM) I/O RDT: unsupported Remote Memory Bandwidth (RMEM) (calculated) I/O RDT: unsupported PMU events: LLC misses LLC references Instructions/Clock (IPC) Allocation Cache Allocation Technology (CAT) L3 CAT CDP: disabled Non-Contiguous CBM: supported I/O RDT: unsupported Num COS: 16 Memory Bandwidth Allocation (MBA) Num COS: 16 CTRL: unsupported Slow Memory Bandwidth Allocation (SMBA) Num COS: 16 CTRL: unsupported $ sudo pqos -D Selected interface: OS WARN: Could not obtain ERDT table OS capabilities (Linux kernel 7.2.0-rc3+) Monitoring Cache Monitoring Technology (CMT) events: LLC Occupancy (LLC) I/O RDT: unsupported scale factor: 1 max rmid: 4096 Memory Bandwidth Monitoring (MBM) events: Local Memory Bandwidth (LMEM) I/O RDT: unsupported scale factor: 1 max rmid: 4096 Total Memory Bandwidth (TMEM) I/O RDT: unsupported scale factor: 1 max rmid: 4096 Remote Memory Bandwidth (RMEM) (calculated) I/O RDT: unsupported scale factor: 1 max rmid: 4096 PMU events: LLC misses scale factor: 1 max rmid: 4096 LLC references scale factor: 1 max rmid: 4096 Instructions/Clock (IPC) scale factor: 1 max rmid: 4096 Allocation Cache Allocation Technology (CAT) L3 CAT CDP: disabled Non-Contiguous CBM: supported I/O RDT: unsupported Num COS: 16 Way size: 2097152 bytes Ways contention bit-mask: 0x0 Min CBM bits: 0 Max CBM bits: 16 Memory Bandwidth Allocation (MBA) Num COS: 16 Granularity: 1 Min B/W: 0 Type: nonlinear MBA 4.0 extensions: unsupported Slow Memory Bandwidth Allocation (SMBA) Num COS: 16 CTRL: unsupported Granularity: 1 Min B/W: 0 Type: nonlinear Cache information L3 Cache Num ways: 16 Way size: 2097152 bytes Num sets: 32768 Line size: 64 bytes Total size: 33554432 bytes L2 Cache Num ways: 16 Way size: 65536 bytes Num sets: 1024 Line size: 64 bytes Total size: 1048576 bytes We know what is the problem. This is because we switched monitoring mode to "mbm_event" which was introduced in kernel v6.18. $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode [mbm_event] default The test works fine when we switch to default mode. $ echo default > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode [default] mbm_event The pqos tool provides the correct MBL and MBR in default mode. I opened this bug to track the issue. We are still discussing in the kernel thread about the resolution. ***@***.***/ Thanks Babu

…

On 7/28/26 03:45, Roman Storozhenko wrote: *rstorozh* left a comment (intel/intel-cmt-cat#311) <https://github.com/ intel/intel-cmt-cat#311#issuecomment-5101930625> Hi Babu, In addition to info requested by Raghavan, please also provide the output of the configuration: pqos/pqos -d and pqos/pqos -D And monitoring: pqos/pqos --iface=OS pqos/pqos -m mbt:0-191 Probably your HW configuration doesn't support remote memory. In this case only MBT count. — Reply to this email directly, view it on GitHub <https://github.com/ intel/intel-cmt-cat#311? email_source=notifications&email_token=AIFLFVBQHYTQPWNJQ4Z6OKL5HBR4JA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTKMJQGE4TGMBWGI22M4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLDGN5XXIZLSL5RWY2LDNM#issuecomment-5101930625>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AIFLFVH7F5OHJ2R4XVI6OWD5HBR4JAVCNFSNUABEKJSXA33TNF2G64TZHMZDQMJUGY2TKOB3JFZXG5LFHM2DSOJRGM2DCMBRG2QXMAQ>. Triage notifications, keep track of coding agent tasks and review pull requests on the go with GitHub Mobile for iOS <https://github.com/ notifications/mobile/ios/ AIFLFVCC4U27CNWSTQU3OD35HBR4JA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTKMJQGE4TGMBWGI22M4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJKTGN5XXIZLSL5UW64Y> and Android <https://github.com/notifications/mobile/android/AIFLFVDT3EALCGXJK7WB2FD5HBR4JA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTKMJQGE4TGMBWGI22M4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLTGN5XXIZLSL5QW4ZDSN5UWI>. Download it today! You are receiving this because you were mentioned.Message ID: <intel/ ***@***.***>

[rstorozh]

@babumoger Thanks, Babu. Now, that I learn about ABMC and kernel discussion context (thanks to Reinette Chatre) I understand the problem much better. Now, let's wait for Borislav feedback:
https://lore.kernel.org/lkml/20260728170423.GAamjhF3W74TW4q9DG@fat_crate.local/
And then discuss further. I also have some ideas how to fix this regardless of the kernel outcome and will come up with the proposal after internal discusssion.