On Mon, May 8, 2017 at 3:56 PM, marcin steć <stecenator(a)gmail.com> wrote:
Journal is not the reason. It's just the first one to hit the
You are correct, it's primarily a kernel issue.
The good news this has improved with Fedora 26, and should improve
some more for F-26 goes GA.
I was getting around 8 MBps on F-25, on F-26 with the same SD card I
can get around 22-24.
Most of these changes won't be coming to F-25 as it's very fiddly and
time consuming to ensure a clean upgrade path so I'll be focusing on
F-26 in that regard.
> It's not logging anything unusual, just normal trafiic.
> But following your suggestion I checked this card in my Lenovo W541 running
> F25. I've got average write speed of around 7MB/s.
> When I sent the same file (2.4 GiB zip) to my PI, and it nearly killed it -
> 1.5 core constantly occupied by system, rest is blocked by IO waits. But
> write speed wasn't so much worse: 4.1 MiB/s.
> Just for curiosity, I wrote the same file onto USB stick attached to my PI -
> this time it was slower (3.2 MiB/s), but system seemed to be more
> So writing is CPU intensive and that makes me wonder what is use_spi_crc
> option responsible for in mmc_core kernel module and how to check it's
> current value.
> After quick look into module's code I see it is supposed to do some data
> validation with crc which I think may lead to lots of CPU intensive
> operations in kernel mode ?
> How do I check "use_spi_crc" current value? I couldn't find any
> files in /proc or /sys filesystems.
> If it's value is "true" than how do I set it to false? Is proper
> /etc/modprobe.d file entry sufficient or should I play with kernel
> parameters at startup since it is responsible for accessing root filesystem
> 2017-05-08 14:55 GMT+02:00 Richard Ryniker <ryniker(a)alum.mit.edu>:
>> If the slowdown is due to log writes, what is written into your journal?
>> It may be awkward to access the journal using the RPi, but move the SD
>> card to another Fedora system (many laptops have flash card readers built
>> in, or use a USB device) and a "smoking gun" may be obvious. The
>> format does not depend on machine architecture. Use the --directory=
>> argument for journalctl.
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