There is a locking problem between different applications reading/writing to resctrlfs directory at the same time (read the patch below for details).
Suggest a standard locking scheme for applications to use. Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com> --- Documentation/x86/intel_rdt_ui.txt.orig 2016-11-30 13:40:33.080233101 -0200 +++ Documentation/x86/intel_rdt_ui.txt 2016-11-30 13:45:01.253703259 -0200 @@ -212,3 +212,30 @@ Finally we move core 4-7 over to the new kernel and the tasks running there get 50% of the cache. # echo C0 > p0/cpus + +4) Locking between applications + +The allocation of an exclusive reservation +of L3 cache involves: + + 1. read list of cbmmasks for each directory + 2. find a contiguous set of bits in the global CBM bitmask + that is clear in any of the directory cbmmasks + 3. create a new directory + 4. set the bits found in step 2 to the new directory "schemata" + file + +If two applications attempt to allocate space race with each other +(if two processes execute the steps above in a interlocked fashion), +they can end up using the same bits of CBMMASK, which renders the +reservations non-exclusive but shared. + +To coordinate creation of reservations on resctrl and avoid the problem +above, the following locking procedure is recommended: + +A) open /var/lock/resctrl/fs.lock with O_CREAT|O_EXCL. +B) if success, write pid of program accessing the directory + structure to this file. +C) read/write the directory structure. +D) remove file. +
