DMA Test Guide¶
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
This small document introduces how to test DMA drivers using dmatest module.
The dmatest module tests DMA memcpy, memset, XOR and RAID6 P+Q operations usingvarious lengths and various offsets into the source and destination buffers. Itwill initialize both buffers with a repeatable pattern and verify that the DMAengine copies the requested region and nothing more. It will also verify thatthe bytes aren’t swapped around, and that the source buffer isn’t modified.
The dmatest module can be configured to test a specific channel. It can alsotest multiple channels at the same time, and it can start multiple threadscompeting for the same channel.
Note
The test suite works only on the channels that have at least onecapability of the following: DMA_MEMCPY (memory-to-memory), DMA_MEMSET(const-to-memory or memory-to-memory, when emulated), DMA_XOR, DMA_PQ.
Note
In case of any related questions use the official mailing listdmaengine@vger.kernel.org.
Part 1 - How to build the test module¶
The menuconfig contains an option that could be found by following path:
Device Drivers -> DMA Engine support -> DMA Test client
In the configuration file the option called CONFIG_DMATEST. The dmatest couldbe built as module or inside kernel. Let’s consider those cases.
Part 2 - When dmatest is built as a module¶
Example of usage:
% modprobe dmatest timeout=2000 iterations=1 channel=dma0chan0 run=1
...or:
% modprobe dmatest% echo 2000 > /sys/module/dmatest/parameters/timeout% echo 1 > /sys/module/dmatest/parameters/iterations% echo dma0chan0 > /sys/module/dmatest/parameters/channel% echo 1 > /sys/module/dmatest/parameters/run
...or on the kernel command line:
dmatest.timeout=2000 dmatest.iterations=1 dmatest.channel=dma0chan0 dmatest.run=1
Example of multi-channel test usage (new in the 5.0 kernel):
% modprobe dmatest% echo 2000 > /sys/module/dmatest/parameters/timeout% echo 1 > /sys/module/dmatest/parameters/iterations% echo dma0chan0 > /sys/module/dmatest/parameters/channel% echo dma0chan1 > /sys/module/dmatest/parameters/channel% echo dma0chan2 > /sys/module/dmatest/parameters/channel% echo 1 > /sys/module/dmatest/parameters/run
Note
For all tests, starting in the 5.0 kernel, either single- or multi-channel,the channel parameter(s) must be set after all other parameters. It is atthat time that the existing parameter values are acquired for use by thethread(s). All other parameters are shared. Therefore, if changes are madeto any of the other parameters, and an additional channel specified, the(shared) parameters used for all threads will use the new values.After the channels are specified, each thread is set as pending. All threadsbegin execution when the run parameter is set to 1.
Hint
A list of available channels can be found by running the following command:
% ls -1 /sys/class/dma/
Once started a message like “ dmatest: Added 1 threads using dma0chan0” isemitted. A thread for that specific channel is created and is now pending, thepending thread is started once run is to 1.
Note that running a new test will not stop any in progress test.
The following command returns the state of the test.
% cat /sys/module/dmatest/parameters/run
To wait for test completion userspace can poll ‘run’ until it is false, or usethe wait parameter. Specifying ‘wait=1’ when loading the module causes moduleinitialization to pause until a test run has completed, while reading/sys/module/dmatest/parameters/wait waits for any running test to completebefore returning. For example, the following scripts wait for 42 teststo complete before exiting. Note that if ‘iterations’ is set to ‘infinite’ thenwaiting is disabled.
Example:
% modprobe dmatest run=1 iterations=42 wait=1% modprobe -r dmatest
...or:
% modprobe dmatest run=1 iterations=42% cat /sys/module/dmatest/parameters/wait% modprobe -r dmatest
Part 3 - When built-in in the kernel¶
The module parameters that is supplied to the kernel command line will be usedfor the first performed test. After user gets a control, the test could bere-run with the same or different parameters. For the details see the abovesectionPart 2 - When dmatest is built as a module.
In both cases the module parameters are used as the actual values for the testcase. You always could check them at run-time by running
% grep -H . /sys/module/dmatest/parameters/*
Part 4 - Gathering the test results¶
Test results are printed to the kernel log buffer with the format:
"dmatest: result <channel>: <test id>: '<error msg>' with src_off=<val> dst_off=<val> len=<val> (<err code>)"
Example of output:
% dmesg | tail -n 1dmatest: result dma0chan0-copy0: #1: No errors with src_off=0x7bf dst_off=0x8ad len=0x3fea (0)
The message format is unified across the different types of errors. Anumber in the parentheses represents additional information, e.g. errorcode, error counter, or status. A test thread also emits a summary line atcompletion listing the number of tests executed, number that failed, and aresult code.
Example:
% dmesg | tail -n 1dmatest: dma0chan0-copy0: summary 1 test, 0 failures 1000 iops 100000 KB/s (0)
The details of a data miscompare error are also emitted, but do not follow theabove format.
Part 5 - Handling channel allocation¶
Allocating Channels¶
Channels do not need to be configured prior to starting a test run. Attemptingto run the test without configuring the channels will result in testing anychannels that are available.
Example:
% echo 1 > /sys/module/dmatest/parameters/rundmatest: No channels configured, continue with any
Channels are registered using the “channel” parameter. Channels can be requested by theirname, once requested, the channel is registered and a pending thread is added to the test list.
Example:
% echo dma0chan2 > /sys/module/dmatest/parameters/channeldmatest: Added 1 threads using dma0chan2
More channels can be added by repeating the example above.Reading back the channel parameter will return the name of last channel that was added successfully.
Example:
% echo dma0chan1 > /sys/module/dmatest/parameters/channeldmatest: Added 1 threads using dma0chan1% echo dma0chan2 > /sys/module/dmatest/parameters/channeldmatest: Added 1 threads using dma0chan2% cat /sys/module/dmatest/parameters/channeldma0chan2
Another method of requesting channels is to request a channel with an empty string, Doing sowill request all channels available to be tested:
Example:
% echo "" > /sys/module/dmatest/parameters/channeldmatest: Added 1 threads using dma0chan0dmatest: Added 1 threads using dma0chan3dmatest: Added 1 threads using dma0chan4dmatest: Added 1 threads using dma0chan5dmatest: Added 1 threads using dma0chan6dmatest: Added 1 threads using dma0chan7dmatest: Added 1 threads using dma0chan8
At any point during the test configuration, reading the “test_list” parameter willprint the list of currently pending tests.
Example:
% cat /sys/module/dmatest/parameters/test_listdmatest: 1 threads using dma0chan0dmatest: 1 threads using dma0chan3dmatest: 1 threads using dma0chan4dmatest: 1 threads using dma0chan5dmatest: 1 threads using dma0chan6dmatest: 1 threads using dma0chan7dmatest: 1 threads using dma0chan8
Note: Channels will have to be configured for each test run as channel configurations do notcarry across to the next test run.
Releasing Channels¶
Channels can be freed by setting run to 0.
Example:
% echo dma0chan1 > /sys/module/dmatest/parameters/channeldmatest: Added 1 threads using dma0chan1% cat /sys/class/dma/dma0chan1/in_use1% echo 0 > /sys/module/dmatest/parameters/run% cat /sys/class/dma/dma0chan1/in_use0
Channels allocated by previous test runs are automatically freed when a newchannel is requested after completing a successful test run.