I noticed that the code in commit.c of the jbd system can waste CPU
cycles. The offending code is as follows.
static int inverted_lock(journal_t *journal, struct buffer_head *bh)
{
if (!jbd_trylock_bh_state(bh)) {
spin_unlock(&journal->j_list_lock);
schedule();
return 0;
}
return 1;
}
[...]
void journal_commit_transaction(journal_t *journal)
{
[...]
write_out_data:
cond_resched();
spin_lock(&journal->j_list_lock);
while (commit_transaction->t_sync_datalist) {
struct buffer_head *bh;
jh = commit_transaction->t_sync_datalist;
commit_transaction->t_sync_datalist = jh->b_tnext;
bh = jh2bh(jh);
if (buffer_locked(bh)) {
BUFFER_TRACE(bh, "locked");
if (!inverted_lock(journal, bh))
goto write_out_data;
This code makes a loop if the jbd_trylock_bh_state fails. This code will
wait till whoever owns the lock releases it. But it is really in a busy
loop and will only be interrupted when the kjournald uses up all its
quota. So it's basically just wasting CPU cycles here. The following
patch should fix this.
Signed-off-by: Steven Rostedt [email protected]
---
--- a/fs/jbd/commit.c 2005-07-11 17:51:37.000000000 -0400
+++ b/fs/jbd/commit.c 2005-07-11 17:51:58.000000000 -0400
@@ -87,7 +87,7 @@ static int inverted_lock(journal_t *jour
{
if (!jbd_trylock_bh_state(bh)) {
spin_unlock(&journal->j_list_lock);
- schedule();
+ yield();
return 0;
}
return 1;
-
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