Hi Tom,
On Tue, Nov 03, 2015 at 07:47:52PM -0600, Tom Zanussi wrote:
> Hi Namhyung,
>
> On Mon, 2015-11-02 at 16:08 +0900, Namhyung Kim wrote:
> > I thought it'd be better if users can see which one is the real drop
> > or not. IOW if drop count is much smaller than the normal event
> > count, [s]he might want to ignore the occasional drops. Otherwise,
> > [s]he should restart with a bigger table. This requires accurate
> > counts of events and drops though.
> >
>
> OK, how about the below - it basically moves the drops set/test/inc into
> tracing_map_insert(), as well as a total hits count. So those values
> will be available for users to use in deciding whether to use the data
> or restart with a bigger table, and the loop is bailed out of only if no
> matching keys are found and there are drops, so callers can continue
> updating existing entries.
But if a key didn't get a desired index, it'd still fail to update..
>
> Users who want the original behavior still get the NULL return and can
> stop calling tracing_map_insert() as before:
>
> struct tracing_map_elt *tracing_map_insert(struct tracing_map *map, void *key)
> {
> u32 idx, key_hash, test_key;
> struct tracing_map_entry *entry;
>
> key_hash = jhash(key, map->key_size, 0);
> if (key_hash == 0)
> key_hash = 1;
> idx = key_hash >> (32 - (map->map_bits + 1));
>
> while (1) {
> idx &= (map->map_size - 1);
> entry = TRACING_MAP_ENTRY(map->map, idx);
> test_key = entry->key;
>
> if (test_key && test_key == key_hash && entry->val &&
> keys_match(key, entry->val->key, map->key_size)) {
> atomic64_inc(&map->hits);
> return entry->val;
> }
>
> if (atomic64_read(&map->drops)) {
> atomic64_inc(&map->drops);
> break;
> }
IMHO it should be removed.
>
> if (!test_key && !cmpxchg(&entry->key, 0, key_hash)) {
> struct tracing_map_elt *elt;
>
> elt = get_free_elt(map);
> if (!elt) {
> atomic64_inc(&map->drops);
And reset entry->key here..
> break;
> }
> memcpy(elt->key, key, map->key_size);
> entry->val = elt;
>
> atomic64_inc(&map->hits);
> return entry->val;
> }
> idx++;
> }
>
> return NULL;
> }
Then tracing_map_lookup() can be implemented like *_insert but bail out
from the loop if test_key is 0. The caller might do like this:
if (!atomic64_read(&map->drops))
elt = tracing_map_insert(...);
else
elt = tracing_map_lookup(...);
Thanks,
Namhyung
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