mboxd_windows: Reset evicted windows
After copying a portion of the backing store to a window,
create_map_window() "resizes" the window to the aligned-up size reported
by copy_flash(). This allows use of the window size as the content size
elsewhere in the codebase.
However, if we needed to evict a window to satisfy a request, the window
properties were not reset. This lead to inefficient use of the reserved
memory by limiting the effective window size to the minimum size of all
requests that were previously allocated the window in question.
Inefficient use of reserved memory isn't the only side effect; the host
takes an eye-watering hit to throughput that gets exponentionally
worse over time:
From the petitboot shell without the patch applied:
/ # time cat /dev/mtd0 > /dev/null
real 0m 49.77s
user 0m 0.00s
sys 0m 49.76s
/ # time cat /dev/mtd0 > /dev/null
real 1m 33.57s
user 0m 0.00s
sys 1m 33.55s
/ # time cat /dev/mtd0 > /dev/null
real 4m 45.37s
user 0m 0.00s
sys 4m 45.35s
/ # time cat /dev/mtd0 > /dev/null
real 9m 17.77s
user 0m 0.00s
sys 9m 17.76s
/ #
And with the patch applied:
/ # time cat /dev/mtd0 > /dev/null
real 0m 43.00s
user 0m 0.00s
sys 0m 42.99s
/ # time cat /dev/mtd0 > /dev/null
real 0m 42.40s
user 0m 0.00s
sys 0m 42.39s
/ # time cat /dev/mtd0 > /dev/null
real 0m 42.41s
user 0m 0.00s
sys 0m 42.39s
/ #
Reset the properties to allow use of the entire reserved memory region
allocated to the window, improving memory efficiency, throughput, and
minimising throughput variance.
Change-Id: I7be78ec5e0a9ee0caf31133b0861e333844b8975
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/mboxd_windows.c b/mboxd_windows.c
index 9742180..275f38a 100644
--- a/mboxd_windows.c
+++ b/mboxd_windows.c
@@ -568,6 +568,7 @@
if (!cur) {
MSG_DBG("No uninitialised window, evicting one\n");
cur = find_oldest_window(context);
+ reset_window(context, cur);
}
/*