Re: RE: RE: [PATCH 1/2] x86/resctrl, Documentation: Keep mbm_assign_mode "default" on boot
From: Babu Moger
Date: Tue Jul 28 2026 - 16:44:05 EST
Hi Tony,
On 7/28/26 15:24, Luck, Tony wrote:
When an RMID is reallocated, the hardware detects the state transition and the first read returns "Unavailable". At that point, the counter is reset and begins counting again from 0. This is the expected behavior on AMD systems. Therefore, setting prev_msr to 0 is the correct behavior.1) Does it start over from zero?
Seems a sane option.
2) Or does the monitor group see whatever the counter was at
when being used by some other group?
Seems less sane.
As per this code, it should start over from 0.
} else if (ret == -EINVAL) {
am = get_arch_mbm_state(hw_dom, rmid, eventid);
if (am)
am->prev_msr = 0;
}
Nope. If you want the value reported to the user to start over from zero,
then prev_msr should be set to the current value of the counter. That
would make the next read start from zero.
Thanks
Babu