On 12/21/12 11:46 AM, Theodore Ts'o wrote: > On Fri, Dec 21, 2012 at 11:01:58AM -0600, Eric Sandeen wrote: >>> I'm also really puzzled about how Eric's patch makes a 10% different >>> on the AIM7 benchmark; as you've pointed out, that will just cause an >>> extra wakeup of the jbd/jbd2 thread, which should then quickly check >>> and decide to go back to sleep. >> >> Ted, just to double check - is that some wondering aloud, or a NAK >> of the original patch? :) > > I'm still thinking.... Things that I don't understand worry me, since > there's a possibility there's more going on than we think. > > Did you have a chance to have your perf people enable the the > jbd2_run_stats tracepoint, to see how the stats change with and > without the patch? Getting back to this; grabbing this over a whole AIM7 run would be huge. I wonder if a few snapshots will be illustrative. We can try. > It would be interesting to see how the stats change --- in particular, > whether the number of blocks logged per transaction is changing, > and/or the number of blocks per transaction is changing. It would > also be interesting to insert a tracepoint in kjournald so we can > track the number of times when kjournald is waking, but ends up *not* > triggering a commit due to the commit timeout firing or > j_commit_sequence != j_commit_request. Ok, I think I can do that w/ systemtap. > I'll probably take the patch on the grounds that it's obvious, but if > you could get your perf folks to run the experiment, I'd really > appreciate it, just so we can understand what might be going on. > Perhaps there's an opportunity for further optimizations, or we'll > find that something unexpected that is evidence of a bug. (Or maybe > it's just a bug in our understanding, but that's also good to get > fixed. :-) I'll see what I can do. -Eric > - Ted > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
