Hi Randy, On 2/19/2018 1:27 PM, Randy Dunlap wrote: > On 02/13/18 07:46, Reinette Chatre wrote: >> Add description of Cache Pseudo-Locking feature, its interface, >> as well as an example of its usage. >> >> Signed-off-by: Reinette Chatre <reinette.cha...@intel.com> >> --- >> Documentation/x86/intel_rdt_ui.txt | 229 >> ++++++++++++++++++++++++++++++++++++- >> 1 file changed, 228 insertions(+), 1 deletion(-) >> >> diff --git a/Documentation/x86/intel_rdt_ui.txt >> b/Documentation/x86/intel_rdt_ui.txt >> index 756fd76b78a6..bb3d6fe0a3e4 100644 >> --- a/Documentation/x86/intel_rdt_ui.txt >> +++ b/Documentation/x86/intel_rdt_ui.txt > >> @@ -329,6 +332,149 @@ L3CODE:0=fffff;1=fffff;2=fffff;3=fffff >> L3DATA:0=fffff;1=fffff;2=3c0;3=fffff >> L3CODE:0=fffff;1=fffff;2=fffff;3=fffff >> >> +Cache Pseudo-Locking >> +-------------------- >> +CAT enables a user to specify the amount of cache space into which an > > space that an
Will fix. > >> +application can fill. Cache pseudo-locking builds on the fact that a >> +CPU can still read and write data pre-allocated outside its current >> +allocated area on a cache hit. With cache pseudo-locking, data can be >> +preloaded into a reserved portion of cache that no application can >> +fill, and from that point on will only serve cache hits. The cache >> +pseudo-locked memory is made accessible to user space where an >> +application can map it into its virtual address space and thus have >> +a region of memory with reduced average read latency. >> + >> +Cache pseudo-locking increases the probability that data will remain >> +in the cache via carefully configuring the CAT feature and controlling >> +application behavior. There is no guarantee that data is placed in >> +cache. Instructions like INVD, WBINVD, CLFLUSH, etc. can still evict >> +“locked” data from cache. Power management C-states may shrink or >> +power off cache. It is thus recommended to limit the processor maximum >> +C-state, for example, by setting the processor.max_cstate kernel parameter. >> + >> +It is required that an application using a pseudo-locked region runs >> +with affinity to the cores (or a subset of the cores) associated >> +with the cache on which the pseudo-locked region resides. This is >> +enforced by the implementation. >> + >> +Pseudo-locking is accomplished in two stages: >> +1) During the first stage the system administrator allocates a portion >> + of cache that should be dedicated to pseudo-locking. At this time an >> + equivalent portion of memory is allocated, loaded into allocated >> + cache portion, and exposed as a character device. >> +2) During the second stage a user-space application maps (mmap()) the >> + pseudo-locked memory into its address space. >> + >> +Cache Pseudo-Locking Interface >> +------------------------------ >> +Platforms supporting cache pseudo-locking will expose a new >> +"/sys/fs/restrl/pseudo_lock" directory after successful mount of the >> +resctrl filesystem. Initially this directory will contain a single file, >> +"avail" that contains the schemata, one line per resource, of cache region >> +available for pseudo-locking. > > uh, sysfs is supposed to be one value per file. This builds on how the schemata file currently works. >> +A pseudo-locked region is created by creating a new directory within >> +/sys/fs/resctrl/pseudo_lock. On success two new files will appear in >> +the directory: >> + >> +"schemata": >> + Shows the schemata representing the pseudo-locked cache region. >> + User writes schemata of requested locked area to file. > > use complete sentences, please. E.g.: > > The user writes the schemata of the requested locked area to the file. > >> + Only one id of single resource accepted - can only lock from > > of a single resource is accepted - > Will fix both. >> + single cache instance. Writing of schemata to this file will >> + return success on successful pseudo-locked region setup. >> +"size": >> + After successful pseudo-locked region setup this read-only file >> + will contain the size in bytes of pseudo-locked region. > > Thank you very much for taking a look! Reinette
