plugins: new hwprofile plugin

This is a plugin intended to help with profiling access to various
bits of system hardware. It only really makes sense for system
emulation.

It takes advantage of the recently exposed helper API that allows us
to see the device name (memory region name) associated with a device.

You can specify arg=read or arg=write to limit the tracking to just
reads or writes (by default it does both).

The pattern option:

  -plugin ./tests/plugin/libhwprofile.so,arg=pattern

will allow you to see the access pattern to devices, eg:

  gic_cpu @ 0xffffffc010040000
    off:00000000, 8, 1, 8, 1
    off:00000000, 4, 1, 4, 1
    off:00000000, 2, 1, 2, 1
    off:00000000, 1, 1, 1, 1

The source option:

  -plugin ./tests/plugin/libhwprofile.so,arg=source

will track the virtual source address of the instruction making the
access:

  pl011 @ 0xffffffc010031000
    pc:ffffffc0104c785c, 1, 4, 0, 0
    pc:ffffffc0104c7898, 1, 4, 0, 0
    pc:ffffffc010512bcc, 2, 1867, 0, 0

You cannot mix source and pattern.

Finally the match option allow you to limit the tracking to just the
devices you care about.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Robert Foley <robert.foley@linaro.org>
Reviewed-by: Robert Foley <robert.foley@linaro.org>
Message-Id: <20210213130325.14781-4-alex.bennee@linaro.org>

1 files changed, 34 insertions, 0 deletions

diff --git a/docs/devel/tcg-plugins.rst b/docs/devel/tcg-plugins.rst
index 0568dfa6a4..39ce86ed96 100644
--- a/docs/devel/tcg-plugins.rst
+++ b/docs/devel/tcg-plugins.rst
@@ -280,3 +280,37 @@ which will eventually report::
     previously @ 0x000000ffd08098/5 (809900593 insns)
     previously @ 0x000000ffd080c0/1 (809900588 insns)
 
+- contrib/plugins/hwprofile
+
+The hwprofile tool can only be used with system emulation and allows
+the user to see what hardware is accessed how often. It has a number of options:
+
+ * arg=read or arg=write
+
+ By default the plugin tracks both reads and writes. You can use one
+ of these options to limit the tracking to just one class of accesses.
+
+ * arg=source
+
+ Will include a detailed break down of what the guest PC that made the
+ access was. Not compatible with arg=pattern. Example output::
+
+   cirrus-low-memory @ 0xfffffd00000a0000
+    pc:fffffc0000005cdc, 1, 256
+    pc:fffffc0000005ce8, 1, 256
+    pc:fffffc0000005cec, 1, 256
+
+ * arg=pattern
+
+ Instead break down the accesses based on the offset into the HW
+ region. This can be useful for seeing the most used registers of a
+ device. Example output::
+
+    pci0-conf @ 0xfffffd01fe000000
+      off:00000004, 1, 1
+      off:00000010, 1, 3
+      off:00000014, 1, 3
+      off:00000018, 1, 2
+      off:0000001c, 1, 2
+      off:00000020, 1, 2
+      ...