10-30-2014
Often cache is just reloaded from the lower, slower layers on the new core, and eventually snooped empty on the old core when the data is modified. This means that while a different core may be available at an instant, it is better to wait a bit for the old core, which may not be 100% busy in the longer term. Of course, some caches cache keyed on virtual addresses, not physical ones, and may be flushed when other processes use the core. For them, dispatching multiple threads of the same process in succession reduces cache flushing. So, while you have asked for concurrent threads, that might actually be made less true in the fine by the system.
Hyperthreading is only for same-process threads, as they share the same virtual space. It is a nice way to increase use of CPU resources, with some added delay when threads' needs collide. It is an interesting alternate direction to the trend in modern CPU design to do speculative operations that are 50% or more a waste of the resource, but speed the critical thread. I find it reminiscent of the old Honeywell-800, where the CPU ran instructions of up to 8 threads more or less in rotation. (If you loaded the accumulator, it did not 'hunt', so many programmers used the accumulator as a register to hog the CPU and speed their thread.) I used to fix this stuff, before it crawled inside a chip!
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TUNA(8) System Administration Utilities TUNA(8)
NAME
tuna - program for tuning running processes
SYNOPSIS
tuna [OPTIONS]
DESCRIPTION
This manual page explains the tuna program. The program can be used to change the attributes of application and kernel threads. The tuna
can operate on IRQs by name or number, and tasks or threads by process ID or command-line. CPUs and sets of CPUs can be specified by CPU or
socket number. IRQ names and process command-lines can include wildcards.
tuna can change scheduling policy, scheduler priority and processor affinity for processes and process threads. tuna can also change the
processor affinity for interrupts. When tuna is invoked without any options it starts up in its graphical interface mode. This manual page
explains only the command-line options for tuna
OPTIONS
tuna has both action options and modifier options. Modifier options must be specified on the command-line before the actions they are
intended to modify. Any modifier option applies to following actions on the same command-line until it is over-ridden.
Actions
-h, --help
Print a list of options. tuna will exit after this action, ignoring the remainder of the command-line.
-g, --gui
Start the GUI. Actions that follow this on the command-line will be processed without waiting for the GUI to complete.
-a, --config_file_apply=profilename
Apply changes described in profile
-l, --config_file_list
List preloaded profiles
-i, --isolate
Move all threads away from CPU-LIST. Requires -c or -S.
-I, --include
Allow all threads to run on CPU-LIST. Requires -c or -S.
-m, --move
Move selected entities to CPU-LIST. Requires -c and either -t or -q.
-p, --priority=[POLICY:]RTPRIO
Set thread scheduler tunables: POLICY and RTPRIO. POLICY is one of OTHER, FIFO, RR, or BATCH. Requires -t.
-P, --show_threads
Show thread list.
-s, --save=FILENAME
Save kthreads sched tunables to FILENAME.
-v, --version
Show version
-W, --what_is
Provides help about selected entities. Requires -t.
-x, --spread
Spread selected entities over CPU-LIST. Requires at least one of -t or -q. The specified threads and IRQs are each assigned to one
cpu in CPU-LIST.
Modifiers
-c, --cpus=CPU-LIST
CPU-LIST affected by commands. Requires a CPU number or a comma-separated list of CPU numbers.
-C, --affect_children
Operation will affect children threads.
-f, --filter
Disable display of selected CPUs in --gui. Requires -c
-G, --cgroup
Display the processes with the type of cgroups they are in. Requires -P
-K, --no_kthreads
Operations will not affect kernel threads.
-q, --irqs=IRQ-LIST
IRQ-LIST affected by commands. Requires an IRQ number or a comma-separated list of IRQ numbers.
-S, --sockets=CPU-SOCKET-LIST
CPU-SOCKET-LIST affected by commands. Requires a socket number or a comma-separated list of socket numbers.
-t, --threads=THREAD-LIST
THREAD-LIST affected by commands. Requires a thread number or thread name, or a comma-separated list of thread numbers and/or names.
Thread names may contain wildcards. Be sure to quote or escape any wildcard specifications.
-U, --no_uthreads
Operations will not affect user threads.
USAGE EXAMPLES
If for instance the Ethernet NICs have multiple queues for both receive and transmit, each with its own IRQ, the Ethernet IRQs can be asso-
ciated with a CPU socket:
tuna -S 2 -i -q 'eth*' -x
Move everything off the CPUs in socket 2, then spread the IRQs for the Ethernet devices acrross those same CPUs.
tuna February 2010 TUNA(8)