On Tue, Oct 3, 2023 at 11:30 PM Tony Luck <tony.luck@xxxxxxxxx> wrote: > > With Sub-NUMA Cluster mode enabled the scope of monitoring resources is > per-NODE instead of per-L3 cache. Suffixes of directories with "L3" in > their name refer to Sub-NUMA nodes instead of L3 cache ids. > > Users should be aware that SNC mode also affects the amount of L3 cache > available for allocation within each SNC node. > > Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx> > > --- > > Changes since v5: > > Added addtional details about challenges tracking tasks when SNC > mode is enabled. > > --- > diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst > index cb05d90111b4..222c507089a5 100644 > --- a/Documentation/arch/x86/resctrl.rst > +++ b/Documentation/arch/x86/resctrl.rst > @@ -345,9 +345,9 @@ When control is enabled all CTRL_MON groups will also contain: > When monitoring is enabled all MON groups will also contain: > > "mon_data": > - This contains a set of files organized by L3 domain and by > - RDT event. E.g. on a system with two L3 domains there will > - be subdirectories "mon_L3_00" and "mon_L3_01". Each of these > + This contains a set of files organized by L3 domain or by NUMA > + node (depending on whether Sub-NUMA Cluster (SNC) mode is disabled > + or enabled respectively) and by RDT event. Each of these > directories have one file per event (e.g. "llc_occupancy", > "mbm_total_bytes", and "mbm_local_bytes"). In a MON group these > files provide a read out of the current value of the event for > @@ -452,6 +452,23 @@ and 0xA are not. On a system with a 20-bit mask each bit represents 5% > of the capacity of the cache. You could partition the cache into four > equal parts with masks: 0x1f, 0x3e0, 0x7c00, 0xf8000. > > +Notes on Sub-NUMA Cluster mode > +============================== > +When SNC mode is enabled Linux may load balance tasks between Sub-NUMA > +nodes much more readily than between regular NUMA nodes since the CPUs > +on Sub-NUMA nodes share the same L3 cache and the system may report > +the NUMA distance between Sub-NUMA nodes with a lower value than used > +for regular NUMA nodes. Users who do not bind tasks to the CPUs of a > +specific Sub-NUMA node must read the "llc_occupancy", "mbm_total_bytes", > +and "mbm_local_bytes" for all Sub-NUMA nodes where the tasks may execute > +to get the full view of traffic for which the tasks were the source. > + > +The cache allocation feature still provides the same number of > +bits in a mask to control allocation into the L3 cache. But each > +of those ways has its capacity reduced because the cache is divided > +between the SNC nodes. The values reported in the resctrl > +"size" files are adjusted accordingly. > + > Memory bandwidth Allocation and monitoring > ========================================== > Sounds better, thanks. Reviewed-by: Peter Newman <peternewman@xxxxxxxxxx>
