On Fri, 2 May 2025 09:45:09 +0100 <shiju.jose@xxxxxxxxxx> wrote: > From: Shiju Jose <shiju.jose@xxxxxxxxxx> > > Update the Documentation/edac/scrub.rst to include use cases and > policies for CXL memory device-based, CXL region-based patrol scrub > control and CXL Error Check Scrub (ECS). > > Signed-off-by: Shiju Jose <shiju.jose@xxxxxxxxxx> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> > --- > Documentation/edac/scrub.rst | 76 ++++++++++++++++++++++++++++++++++++ > 1 file changed, 76 insertions(+) > > diff --git a/Documentation/edac/scrub.rst b/Documentation/edac/scrub.rst > index daab929cdba1..89a33ef3fde3 100644 > --- a/Documentation/edac/scrub.rst > +++ b/Documentation/edac/scrub.rst > @@ -264,3 +264,79 @@ Sysfs files are documented in > `Documentation/ABI/testing/sysfs-edac-scrub` > > `Documentation/ABI/testing/sysfs-edac-ecs` > + > +Examples > +-------- > + > +The usage takes the form shown in these examples: > + > +1. CXL memory Patrol Scrub > + > +The following are the use cases identified why we might increase the scrub rate. > + > +- Scrubbing is needed at device granularity because a device is showing > + unexpectedly high errors. > + > +- Scrubbing may apply to memory that isn't online at all yet. Likely this > + is a system wide default setting on boot. > + > +- Scrubbing at a higher rate because the monitor software has determined that > + more reliability is necessary for a particular data set. This is called > + Differentiated Reliability. > + > +1.1. Device based scrubbing > + > +CXL memory is exposed to memory management subsystem and ultimately userspace > +via CXL devices. Device-based scrubbing is used for the first use case > +described in "Section 1 CXL Memory Patrol Scrub". > + > +When combining control via the device interfaces and region interfaces, > +"see Section 1.2 Region based scrubbing". > + > +Sysfs files for scrubbing are documented in > +`Documentation/ABI/testing/sysfs-edac-scrub` > + > +1.2. Region based scrubbing > + > +CXL memory is exposed to memory management subsystem and ultimately userspace > +via CXL regions. CXL Regions represent mapped memory capacity in system > +physical address space. These can incorporate one or more parts of multiple CXL > +memory devices with traffic interleaved across them. The user may want to control > +the scrub rate via this more abstract region instead of having to figure out the > +constituent devices and program them separately. The scrub rate for each device > +covers the whole device. Thus if multiple regions use parts of that device then > +requests for scrubbing of other regions may result in a higher scrub rate than > +requested for this specific region. > + > +Region-based scrubbing is used for the third use case described in > +"Section 1 CXL Memory Patrol Scrub". > + > +Userspace must follow below set of rules on how to set the scrub rates for any > +mixture of requirements. > + > +1. Taking each region in turn from lowest desired scrub rate to highest and set > + their scrub rates. Later regions may override the scrub rate on individual > + devices (and hence potentially whole regions). > + > +2. Take each device for which enhanced scrubbing is required (higher rate) and > + set those scrub rates. This will override the scrub rates of individual devices, > + setting them to the maximum rate required for any of the regions they help back, > + unless a specific rate is already defined. > + > +Sysfs files for scrubbing are documented in > +`Documentation/ABI/testing/sysfs-edac-scrub` > + > +2. CXL memory Error Check Scrub (ECS) > + > +The Error Check Scrub (ECS) feature enables a memory device to perform error > +checking and correction (ECC) and count single-bit errors. The associated > +memory controller sets the ECS mode with a trigger sent to the memory > +device. CXL ECS control, allows the host, thus the userspace, to change the > +attributes for error count mode, threshold number of errors per segment > +(indicating how many segments have at least that number of errors) for > +reporting errors, and reset the ECS counter. Thus, the responsibility for > +initiating Error Check Scrub on a memory device may lie with the memory > +controller or platform when unexpectedly high error rates are detected. > + > +Sysfs files for scrubbing are documented in > +`Documentation/ABI/testing/sysfs-edac-ecs`
