Hi Babu, On 7/10/25 10:16 AM, Babu Moger wrote: > > This series adds the support for L3 Smart Data Cache Injection Allocation > Enforcement (SDCIAE) to resctrl infrastructure. It is referred to as > "io_alloc" in resctrl subsystem. > > Upcoming AMD hardware implements Smart Data Cache Injection (SDCI). > Smart Data Cache Injection (SDCI) is a mechanism that enables direct > insertion of data from I/O devices into the L3 cache. By directly caching > data from I/O devices rather than first storing the I/O data in DRAM, SDCI > reduces demands on DRAM bandwidth and reduces latency to the processor > consuming the I/O data. > > The SDCIAE (SDCI Allocation Enforcement) PQE feature allows system software > to control the portion of the L3 cache used for SDCI devices. > > When enabled, SDCIAE forces all SDCI lines to be placed into the L3 cache > partitions identified by the highest-supported L3_MASK_n register, where n > is the maximum supported CLOSID. Even though this CLOSID use is unique to AMD this implementation makes it part of resctrl fs's support of io_alloc. It is confusing to have architectural specific features be handled by resctrl fs so I think it will be useful to add a snippet here to help folks trying to decipher this work. Consider for example a snippet like: Since CLOSIDs are managed by resctrl fs it is least invasive to make the "io_alloc is supported by maximum supported CLOSID" part of the initial resctrl fs support for io_alloc. Take care not to expose this use of CLOSID for io_alloc to user space so that this is not required from other architectures that may support io_alloc differently in the future. > > The feature details are documented in the APM listed below [1]. > [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming > Publication # 24593 Revision 3.41 section 19.4.7 L3 Smart Data Cache > Injection Allocation Enforcement (SDCIAE) > Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 > > The feature requires linux support of TPH (TLP Processing Hints). > The support is available in linux kernel after the commit > 48d0fd2b903e3 ("PCI/TPH: Add TPH documentation") > > The patches are based on top of commit (6.16.0-rc5) > commit b4ec95e3bc3f ("Merge x86/microcode into tip/master") > > # Linux Implementation > > Feature adds following interface files when the resctrl "io_alloc" feature > is supported on the resource: > > /sys/fs/resctrl/info/L3/io_alloc: Report the feature status. Enable/disable the > feature by writing to the interface. > > /sys/fs/resctrl/info/L3/io_alloc_cbm: List the Capacity Bit Masks (CBMs) available > for I/O devices when io_alloc feature is enabled. > Configure the CBM by writing to the interface. > > When CDP is enabled, these files will be created both in L3CODE and L3DATA. "will be" -> "are" > > # Examples: > > a. Check if io_alloc feature is available > # mount -t resctrl resctrl /sys/fs/resctrl/ > > # cat /sys/fs/resctrl/info/L3/io_alloc > disabled > > b. Enable the io_alloc feature. > > # echo 1 > /sys/fs/resctrl/info/L3/io_alloc > # cat /sys/fs/resctrl/info/L3/io_alloc > enabled > > c. Check the CBM values for the io_alloc feature. > > # cat /sys/fs/resctrl/info/L3/io_alloc_cbm > 0=ffff;1=ffff > > d. Change the CBM value for the domain 1: "for the domain 1" -> "of domain 1"? (nit: inconsistent use of "." vs. ":" in items) > # echo 1=FF > /sys/fs/resctrl/info/L3/io_alloc_cbm > > # cat /sys/fs/resctrl/info/L3/io_alloc_cbm > 0=ffff;1=00ff > > d. Disable io_alloc feature and exit. > > # echo 0 > /sys/fs/resctrl/info/L3/io_alloc > # cat /sys/fs/resctrl/info/L3/io_alloc > disabled > > # umount /sys/fs/resctrl/ > > --- Reinette
