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The Read While Write (RWW) feature allows to perform reads from the
flash array into cache while a program (from cache) or an erase
operation happens, provided that the two areas are located on different
banks.
The main benefit is the possible reduced latency when requesting to read
a page while a much longer operation is ongoing, like a write or an
erase.
We can try to compare the positive impact of such a feature by enhancing
the flash_speed test tool with the following test:
- Measure the time taken by an eraseblock write in parallel with an
eraseblock read.
- Measure when the read operation ends.
- Compare the two to get the latency saved with the RWW feature.
To be sure the mtd_write actually starts (and acquires the necessary
locks) before the mtd_read does, we use SCHED_FIFO at rather high
(arbitrary) priorities, respectively 42 and 41.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>
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In order to be able to have interleaved measures, let's not use the
start and finish global variables from the time helpers directly,
provide parameters for these variables so that we can provide either the
global entries, or more specific ones when relevant.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>
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The speed test does reads and writes of different sizes:
- eraseblock
- page
- two pages
At least this is the theory because, as opposed to the legacy kernel
module doing the same measurement, the userspace tool uses the subpage
size (hence accessing the same page 4, 8 or 16 times depending on the
subpage setting). Of course if the controller does not support subpages,
this issue is not visible.
Use mtd.min_io_size instead for non-NOR devices in order to get the
right bandwidth (at least one that fits the logs).
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>
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A common pattern in command line processing is having a usage()
function that prints out how to use the command line options and
then terminates.
The function is typically used inside a switch block for command
line options like `-h' or unknown options. In a lot of places, the
break keyword is omitted, because the function exits anyway. However,
this triggers gcc warnings about implicit fall-through.
Rather than adding a phony "/* fall-through */" this patch flags the
usage() style function with a gcc attribute, indicating that they do
not return and removes further superfluous break statements.
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>
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Basically a user space port of the mtd speed test kernel module.
In addition to the block offset and count module parameters, the
utility supports a block stride and can restore the block contents
after test. Furthermore, a flag can be used to disable destructive
tests (i.e. only perform read speed tests).
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>
Signed-off-by: Richard Weinberger <richard@nod.at>
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