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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. > Sure. >> >> 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" > Sure. >> >> # 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"? Sure. > > (nit: inconsistent use of "." vs. ":" in items) Fixed it. > >> # 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 > > -- Thanks Babu Moger