diff options
Diffstat (limited to 'Documentation/x86')
| -rw-r--r-- | Documentation/x86/intel_rdt_ui.txt | 99 |
1 files changed, 97 insertions, 2 deletions
diff --git a/Documentation/x86/intel_rdt_ui.txt b/Documentation/x86/intel_rdt_ui.txt index a16aa2113840..de913e00e922 100644 --- a/Documentation/x86/intel_rdt_ui.txt +++ b/Documentation/x86/intel_rdt_ui.txt @@ -65,6 +65,27 @@ related to allocation: some platforms support devices that have their own settings for cache use which can over-ride these bits. +"bit_usage": Annotated capacity bitmasks showing how all + instances of the resource are used. The legend is: + "0" - Corresponding region is unused. When the system's + resources have been allocated and a "0" is found + in "bit_usage" it is a sign that resources are + wasted. + "H" - Corresponding region is used by hardware only + but available for software use. If a resource + has bits set in "shareable_bits" but not all + of these bits appear in the resource groups' + schematas then the bits appearing in + "shareable_bits" but no resource group will + be marked as "H". + "X" - Corresponding region is available for sharing and + used by hardware and software. These are the + bits that appear in "shareable_bits" as + well as a resource group's allocation. + "S" - Corresponding region is used by software + and available for sharing. + "E" - Corresponding region is used exclusively by + one resource group. No sharing allowed. Memory bandwitdh(MB) subdirectory contains the following files with respect to allocation: @@ -163,6 +184,16 @@ When control is enabled all CTRL_MON groups will also contain: A list of all the resources available to this group. Each resource has its own line and format - see below for details. +"size": + Mirrors the display of the "schemata" file to display the size in + bytes of each allocation instead of the bits representing the + allocation. + +"mode": + The "mode" of the resource group dictates the sharing of its + allocations. A "shareable" resource group allows sharing of its + allocations while an "exclusive" resource group does not. + When monitoring is enabled all MON groups will also contain: "mon_data": @@ -502,7 +533,71 @@ siblings and only the real time threads are scheduled on the cores 4-7. # echo F0 > p0/cpus -4) Locking between applications +Example 4 +--------- + +The resource groups in previous examples were all in the default "shareable" +mode allowing sharing of their cache allocations. If one resource group +configures a cache allocation then nothing prevents another resource group +to overlap with that allocation. + +In this example a new exclusive resource group will be created on a L2 CAT +system with two L2 cache instances that can be configured with an 8-bit +capacity bitmask. The new exclusive resource group will be configured to use +25% of each cache instance. + +# mount -t resctrl resctrl /sys/fs/resctrl/ +# cd /sys/fs/resctrl + +First, we observe that the default group is configured to allocate to all L2 +cache: + +# cat schemata +L2:0=ff;1=ff + +We could attempt to create the new resource group at this point, but it will +fail because of the overlap with the schemata of the default group: +# mkdir p0 +# echo 'L2:0=0x3;1=0x3' > p0/schemata +# cat p0/mode +shareable +# echo exclusive > p0/mode +-sh: echo: write error: Invalid argument +# cat info/last_cmd_status +schemata overlaps + +To ensure that there is no overlap with another resource group the default +resource group's schemata has to change, making it possible for the new +resource group to become exclusive. +# echo 'L2:0=0xfc;1=0xfc' > schemata +# echo exclusive > p0/mode +# grep . p0/* +p0/cpus:0 +p0/mode:exclusive +p0/schemata:L2:0=03;1=03 +p0/size:L2:0=262144;1=262144 + +A new resource group will on creation not overlap with an exclusive resource +group: +# mkdir p1 +# grep . p1/* +p1/cpus:0 +p1/mode:shareable +p1/schemata:L2:0=fc;1=fc +p1/size:L2:0=786432;1=786432 + +The bit_usage will reflect how the cache is used: +# cat info/L2/bit_usage +0=SSSSSSEE;1=SSSSSSEE + +A resource group cannot be forced to overlap with an exclusive resource group: +# echo 'L2:0=0x1;1=0x1' > p1/schemata +-sh: echo: write error: Invalid argument +# cat info/last_cmd_status +overlaps with exclusive group + +Locking between applications +---------------------------- Certain operations on the resctrl filesystem, composed of read/writes to/from multiple files, must be atomic. @@ -510,7 +605,7 @@ to/from multiple files, must be atomic. As an example, the allocation of an exclusive reservation of L3 cache involves: - 1. Read the cbmmasks from each directory + 1. Read the cbmmasks from each directory or the per-resource "bit_usage" 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 |