trace doc: convert trace/mmiotrace.txt to rst format
This converts the plain text documentation to reStructuredText format and add it into Sphinx TOC tree. No essential content change. Cc: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Changbin Du <changbin.du@intel.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>hifive-unleashed-5.1
Changbin Du
Jonathan Corbet
parent
57e5f29f04
commit
ed657c1cbc
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@ -17,3 +17,4 @@ Linux Tracing Technologies
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events-power
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events-nmi
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events-msr
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mmiotrace
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@ -1,4 +1,6 @@
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In-kernel memory-mapped I/O tracing
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===================================
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In-kernel memory-mapped I/O tracing
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===================================
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Home page and links to optional user space tools:
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@ -31,30 +33,35 @@ is no way to automatically detect if you are losing events due to CPUs racing.
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Usage Quick Reference
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---------------------
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::
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$ mount -t debugfs debugfs /sys/kernel/debug
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$ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer
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$ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt &
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Start X or whatever.
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$ echo "X is up" > /sys/kernel/debug/tracing/trace_marker
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$ echo nop > /sys/kernel/debug/tracing/current_tracer
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Check for lost events.
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$ mount -t debugfs debugfs /sys/kernel/debug
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$ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer
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$ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt &
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Start X or whatever.
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$ echo "X is up" > /sys/kernel/debug/tracing/trace_marker
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$ echo nop > /sys/kernel/debug/tracing/current_tracer
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Check for lost events.
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Usage
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-----
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Make sure debugfs is mounted to /sys/kernel/debug.
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If not (requires root privileges):
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$ mount -t debugfs debugfs /sys/kernel/debug
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If not (requires root privileges)::
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$ mount -t debugfs debugfs /sys/kernel/debug
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Check that the driver you are about to trace is not loaded.
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Activate mmiotrace (requires root privileges):
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$ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer
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Activate mmiotrace (requires root privileges)::
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$ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer
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Start storing the trace::
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$ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt &
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Start storing the trace:
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$ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt &
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The 'cat' process should stay running (sleeping) in the background.
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Load the driver you want to trace and use it. Mmiotrace will only catch MMIO
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@ -66,30 +73,42 @@ This makes it easier to see which part of the (huge) trace corresponds to
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which action. It is recommended to place descriptive markers about what you
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do.
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Shut down mmiotrace (requires root privileges):
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$ echo nop > /sys/kernel/debug/tracing/current_tracer
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Shut down mmiotrace (requires root privileges)::
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$ echo nop > /sys/kernel/debug/tracing/current_tracer
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The 'cat' process exits. If it does not, kill it by issuing 'fg' command and
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pressing ctrl+c.
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Check that mmiotrace did not lose events due to a buffer filling up. Either
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$ grep -i lost mydump.txt
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which tells you exactly how many events were lost, or use
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$ dmesg
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Check that mmiotrace did not lose events due to a buffer filling up. Either::
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$ grep -i lost mydump.txt
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which tells you exactly how many events were lost, or use::
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$ dmesg
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to view your kernel log and look for "mmiotrace has lost events" warning. If
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events were lost, the trace is incomplete. You should enlarge the buffers and
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try again. Buffers are enlarged by first seeing how large the current buffers
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are:
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$ cat /sys/kernel/debug/tracing/buffer_size_kb
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are::
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$ cat /sys/kernel/debug/tracing/buffer_size_kb
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gives you a number. Approximately double this number and write it back, for
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instance:
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$ echo 128000 > /sys/kernel/debug/tracing/buffer_size_kb
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instance::
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$ echo 128000 > /sys/kernel/debug/tracing/buffer_size_kb
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Then start again from the top.
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If you are doing a trace for a driver project, e.g. Nouveau, you should also
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do the following before sending your results:
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$ lspci -vvv > lspci.txt
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$ dmesg > dmesg.txt
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$ tar zcf pciid-nick-mmiotrace.tar.gz mydump.txt lspci.txt dmesg.txt
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do the following before sending your results::
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$ lspci -vvv > lspci.txt
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$ dmesg > dmesg.txt
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$ tar zcf pciid-nick-mmiotrace.tar.gz mydump.txt lspci.txt dmesg.txt
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and then send the .tar.gz file. The trace compresses considerably. Replace
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"pciid" and "nick" with the PCI ID or model name of your piece of hardware
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under investigation and your nickname.
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@ -148,17 +167,18 @@ zero if it is not recorded. PID is always zero as tracing MMIO accesses
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originating in user space memory is not yet supported.
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For instance, the following awk filter will pass all 32-bit writes that target
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physical addresses in the range [0xfb73ce40, 0xfb800000[
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physical addresses in the range [0xfb73ce40, 0xfb800000]
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::
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$ awk '/W 4 / { adr=strtonum($5); if (adr >= 0xfb73ce40 &&
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adr < 0xfb800000) print; }'
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$ awk '/W 4 / { adr=strtonum($5); if (adr >= 0xfb73ce40 &&
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adr < 0xfb800000) print; }'
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Tools for Developers
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--------------------
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The user space tools include utilities for:
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- replacing numeric addresses and values with hardware register names
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- replaying MMIO logs, i.e., re-executing the recorded writes
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- replacing numeric addresses and values with hardware register names
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- replaying MMIO logs, i.e., re-executing the recorded writes
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