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Date: Wed, 9 Sep 2015 12:25:01 -0700 From: Vikas Shivappa <vikas.shivappa@...ux.intel.com> To: vikas.shivappa@...el.com Cc: vikas.shivappa@...ux.intel.com, x86@...nel.org, linux-kernel@...r.kernel.org, hpa@...or.com, tglx@...utronix.de, mingo@...nel.org, tj@...nel.org, peterz@...radead.org, matt.fleming@...el.com, will.auld@...el.com, h.peter.anvin@...el.com, glenn.p.williamson@...el.com, kanaka.d.juvva@...el.com, bruce.schlobohm@...el.com Subject: [PATCH 10/11] x86,cgroup/intel_rdt : Add intel_rdt cgroup documentation Add documentation on using the cache allocation cgroup interface with examples. Signed-off-by: Vikas Shivappa <vikas.shivappa@...ux.intel.com> --- Documentation/cgroups/rdt.txt | 133 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 133 insertions(+) create mode 100644 Documentation/cgroups/rdt.txt diff --git a/Documentation/cgroups/rdt.txt b/Documentation/cgroups/rdt.txt new file mode 100644 index 0000000..bc6b20a --- /dev/null +++ b/Documentation/cgroups/rdt.txt @@ -0,0 +1,133 @@ + RDT + --- + +Copyright (C) 2014 Intel Corporation +Written by vikas.shivappa@...ux.intel.com + +CONTENTS: +========= + +1. Cache Allocation Technology + 1.1 Why is Cache allocation needed? +2. Usage Examples and Syntax + +1. Cache Allocation Technology +=================================== + +1.1 Why is Cache allocation needed +---------------------------------- + +In todays new processors the number of cores is continuously increasing +especially in large scale usage models where VMs are used like +webservers and datacenters. The number of cores increase the number of +threads or workloads that can simultaneously be run. When +multi-threaded-applications, VMs, workloads run concurrently they +compete for shared resources including L3 cache. + +The architecture also allows dynamically changing these subsets during +runtime to further optimize the performance of the higher priority +application with minimal degradation to the low priority app. +Additionally, resources can be rebalanced for system throughput benefit. +This technique may be useful in managing large computer systems which +large L3 cache. + +Cloud/Container use case: +They key use case scenarios are in large server clusters in a typical +cloud or container context. A central 'managing agent' would control +resource allocations to a set of VMs or containers. In todays resource +management, cgroups are widely used already and a significant amount of +plumbing in user space is already done to perform tasks like +allocating/configuring resources dynamically and statically. An +important example is dockers using systemd and systemd inturn using +cgroups in its core to manage resources. This makes cgroup interface an +easily adaptable interface for cache allocation. + +Noisy neighbour use case: +A more specific use case may be when a streaming app which is constantly +copying data and accessing linear space larger than L3 cache +and hence evicting a large amount of cache which could have +otherwise been used by a high priority computing application. Using the +cache allocation feature, the 'noisy neighbours' like the streaming +application can be confined to use a smaller cache and the high priority +application be awarded a larger amount of cache space. A managing agent +can monitor the cache allocation using cache monitoring through libperf +and be able to make resource adjustments either statically or +dynamically. +This interface hence helps in maintaining a resource policy to +provide the quality of service requirements like number of requests +handled, response time. + +More information can be found in the Intel SDM June 2015, Volume 3, +section 17.16. More information on kernel implementation details can be +found in Documentation/x86/intel_rdt.txt. + +2. Usage examples and syntax +============================ + +Following is an example on how a system administrator/root user can +configure L3 cache allocation to threads. + +To enable the cache allocation during compile time set the +CONFIG_INTEL_RDT=y. + +To check if Cache allocation was enabled on your system + $ dmesg | grep -i intel_rdt + intel_rdt: Intel Cache Allocation enabled + + $ cat /proc/cpuinfo +output would have 'rdt' (if rdt is enabled) and 'cat_l3' (if L3 +cache allocation is enabled). + +example1: Following would mount the cache allocation cgroup subsystem +and create 2 directories. + + $ cd /sys/fs/cgroup + $ mkdir rdt + $ mount -t cgroup -ointel_rdt intel_rdt /sys/fs/cgroup/rdt + $ cd rdt + $ mkdir group1 + $ mkdir group2 + +Following are some of the Files in the directory + + $ ls + intel_rdt.l3_cbm + tasks + +Say if the cache is 4MB (looked up from /proc/cpuinfo) and max cbm is 16 +bits (indicated by the root nodes cbm). This assigns 1MB of cache to +group1 and group2 which is exclusive between them. + + $ cd group1 + $ /bin/echo 0xf > intel_rdt.l3_cbm + + $ cd group2 + $ /bin/echo 0xf0 > intel_rdt.l3_cbm + +Assign tasks to the group2 + + $ /bin/echo PID1 > tasks + $ /bin/echo PID2 > tasks + +Now threads PID1 and PID2 get to fill the 1MB of cache that was +allocated to group2. Similarly assign tasks to group1. + +example2: Below commands allocate '1MB L3 cache on socket1 to group1' +and '2MB of L3 cache on socket2 to group2'. +This mounts both cpuset and intel_rdt and hence the ls would list the +files in both the subsystems. + $ mount -t cgroup -ocpuset,intel_rdt cpuset,intel_rdt rdt/ + +Assign the cache + $ /bin/echo 0xf > /sys/fs/cgroup/rdt/group1/intel_rdt.l3_cbm + $ /bin/echo 0xff > /sys/fs/cgroup/rdt/group2/intel_rdt.l3_cbm + +Assign tasks for group1 and group2 + $ /bin/echo PID1 > /sys/fs/cgroup/rdt/group1/tasks + $ /bin/echo PID2 > /sys/fs/cgroup/rdt/group1/tasks + $ /bin/echo PID3 > /sys/fs/cgroup/rdt/group2/tasks + $ /bin/echo PID4 > /sys/fs/cgroup/rdt/group2/tasks + +Tie the group1 to socket1 and group2 to socket2 + $ /bin/echo <cpumask for socket1> > /sys/fs/cgroup/rdt/group1/cpuset.cpus + $ /bin/echo <cpumask for socket2> > /sys/fs/cgroup/rdt/group2/cpuset.cpus -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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