Attachment 1374 Details for Bug 27032 – Memory bandwidth counter width and overflow issue - steps to reproduce

Memory bandwidth counter width and overflow issue - steps to reproduce

Memory bandwidth counter width and overflow issue - steps to reproduce.txt (text/plain), 3.62 KB, created by shenxiaochen on 2025-11-13 13:35:11 UTC

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Creator: shenxiaochen

Created: 2025-11-13 13:35:11 UTC

Size: 3.62 KB

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>Memory bandwidth counter width and overflow issue - steps to reproduce:
>
>1. Run memory bandwidth stress workload (e.g., STREAM) on multiple CPUs to generate memory bandwidth.
>
># taskset -c 0-7 ./stream_c.exe
># pstree -lp | grep stream_c.exe
>           |            |-sshd(4118)---bash(4184)---stream_c.exe(4388)-+-{stream_c.exe}(4389)
>           |            |                                              |-{stream_c.exe}(4390)
>           |            |                                              |-{stream_c.exe}(4391)
>           |            |                                              |-{stream_c.exe}(4392)
>           |            |                                              |-{stream_c.exe}(4393)
>           |            |                                              |-{stream_c.exe}(4394)
>           |            |                                              `-{stream_c.exe}(4395)
>
>
>2. Mount Resctrl Filesystem, create control group "p1", add STREAM workload PIDs/TIDs to p1 group:
>
># mount -t resctrl resctrl /sys/fs/resctrl
># mkdir /sys/fs/resctrl/p1
># ./add_tasks.sh
>-------------------------------------------------------------------------------------
>#/usr/bin/bash
># add_tasks.sh
>
>ID=`ps -efL | grep stream_c.exe | grep -v "grep" | awk '{print $4}'`
>for id in $ID
>do
>        echo $id >/sys/fs/resctrl/p1/tasks
>done
>-------------------------------------------------------------------------------------
>
>
>3. Read memory bandwidth counters with 1 second interval, observe the random unexpected values due to incorrect counter overflow handling:
>
># ./mbm_total_verbose.sh
>-------------------------------------------------------------------------------------
>#/usr/bin/bash
># mbm_total_verbose.sh
>
>total_1=`cat /sys/fs/resctrl/p1/mon_data/mon_L3_00/mbm_total_bytes`
>sleep 1
>while true
>do
>        total_2=`cat /sys/fs/resctrl/p1/mon_data/mon_L3_00/mbm_total_bytes`
>        echo "total b/w (bytes/s):" `expr $total_2 - $total_1` "($total_2 - $total_1)"
>        total_1=$total_2
>        sleep 1
>done
>-------------------------------------------------------------------------------------
>
>total b/w (bytes/s): 21663042304 (222340959424 - 200677917120)
>total b/w (bytes/s): 21951040640 (244292000064 - 222340959424)
>total b/w (bytes/s): 21491510336 (265783510400 - 244292000064)
>total b/w (bytes/s): 1125646660758656 (1125912444269056 - 265783510400)  < == unexpected values due to incorrect counter overflow handling
>total b/w (bytes/s): 21957204096 (1125934401473152 - 1125912444269056)
>total b/w (bytes/s): 21750773184 (1125956152246336 - 1125934401473152)
>total b/w (bytes/s): 21397818496 (1125977550064832 - 1125956152246336)
>total b/w (bytes/s): 21933403264 (1125999483468096 - 1125977550064832)
>total b/w (bytes/s): 21947796032 (1126021431264128 - 1125999483468096)
>total b/w (bytes/s): 21271977152 (1126042703241280 - 1126021431264128)
>total b/w (bytes/s): 21854536000 (1126064557777280 - 1126042703241280)
>total b/w (bytes/s): 21957381568 (1126086515158848 - 1126064557777280)
>total b/w (bytes/s): 21358693184 (1126107873852032 - 1126086515158848)
>total b/w (bytes/s): 21771448640 (1126129645300672 - 1126107873852032)
>total b/w (bytes/s): 21960641920 (1126151605942592 - 1126129645300672)
>total b/w (bytes/s): 21463460352 (1126173069402944 - 1126151605942592)
>total b/w (bytes/s): 1125646683192192 (2251819752595136 - 1126173069402944)  < == unexpected values due to incorrect counter overflow handling
>total b/w (bytes/s): 21958503872 (2251841711099008 - 2251819752595136)
>total b/w (bytes/s): 21731181440 (2251863442280448 - 2251841711099008)
>total b/w (bytes/s): 21410335936 (2251884852616384 - 2251863442280448)

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