Messages in this thread Patch in this message | | | Subject | Re: kjournald wasting CPU in invert_lock fs/jbd/commit.c | From | Steven Rostedt <> | Date | Mon, 11 Jul 2005 19:09:42 -0400 |
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On Mon, 2005-07-11 at 15:41 -0700, Andrew Morton wrote: > Steven Rostedt <rostedt@goodmis.org> wrote: > > > > I noticed that the code in commit.c of the jbd system can waste CPU > > cycles. > > How did you notice? By code inspection or by runtime observation? If the > latter, please share.
Argh! I just realize that this problem is really more in Ingo's RT kernel, but I assumed that it was a problem in vanilla since the code is more from the vanilla kernel. With Ingo's spin_locks as mutexes, this creates a problem on UP, but your are right, this is not a problem for vanilla UP.
> Yeah. But these _are_ spinlocks, so spinning is what's supposed to happen. > Maybe we should dump that silly schedule() and just do cpu_relax(). > Although I do recall once theorising that the time we spend in the > schedule() might be preventing livelocks. >
As mentioned above, this was a confusion of paradigms. I just got back from Europe, so I'm blaming this on jetlag!
OK a cpu_relax() may be better. So here it is :-)
Signed-off-by: Steven Rostedt <rostedt@goodmis.org> --- --- a/fs/jbd/commit.c 2005-07-11 17:51:37.000000000 -0400 +++ b/fs/jbd/commit.c 2005-07-11 19:05:35.000000000 -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(); + cpu_relax(); return 0; } return 1;
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