Re: [PATCH] HID: debug: improve hid_debug_event()
flat view
From: Joe Perches <joe@perches.com>
Date: 2015-11-25 20:32:01
Also in:
lkml
On Tue, 2015-11-24 at 13:33 +0100, Rasmus Villemoes wrote:
The code in hid_debug_event() causes horrible code generation. First, we do a strlen() call for every byte we copy (we're doing a store to global memory, so gcc has no way of proving that strlen(buf) doesn't change). Second, since both i, list->tail and HID_DEBUG_BUFSIZE have signed type, the modulo computation has to take into account the possibility that list->tail+i is negative, so it's not just a simple and. Fix the former by simply not doing strlen() at all (we have to load buf[i] anyway, so testing it is almost free) and the latter by changing i to unsigned. This cuts 29% (69 bytes) of the size of the function.
[]
quoted hunk ↗ jump to hunk
diff --git a/drivers/hid/hid-debug.c b/drivers/hid/hid-debug.c
[]
quoted hunk ↗ jump to hunk
@@ -659,13 +659,13 @@ EXPORT_SYMBOL_GPL(hid_dump_device); /* enqueue string to 'events' ring buffer */ void hid_debug_event(struct hid_device *hdev, char *buf) { - int i; + unsigned i; struct hid_debug_list *list; unsigned long flags; spin_lock_irqsave(&hdev->debug_list_lock, flags); list_for_each_entry(list, &hdev->debug_list, node) { - for (i = 0; i < strlen(buf); i++) + for (i = 0; buf[i]; i++) list->hid_debug_buf[(list->tail + i) % HID_DEBUG_BUFSIZE] = buf[i]; list->tail = (list->tail + i) % HID_DEBUG_BUFSIZE;
trivia:
The code might look nicer if (list->tail + i) % HID_DEBUG_BUFSIZE
was stored into a temporary.
Maybe use an if >= BUFSIZE to avoid a %
Something like:
int pos = list->tail;
for (i = 0; buf[i]; i++) {
list->hid_debug_buf[pos++] = buf[i];
if (pos >= HID_DEBUG_BUFSIZE)
pos = 0;
}
list->tail = pos;