On Tue, Oct 28, 2008 at 03:38:05PM -0600, Andreas Dilger wrote: > On Oct 28, 2008 16:16 -0400, Josef Bacik wrote: > > I also have a min() check in there to make sure we don't sleep longer than > > a jiffie in case our storage is super slow, this was requested by Andrew. > > Is there a particular reason why 1 jiffie is considered the "right amount" > of time to sleep, given this is a kernel config parameter and has nothing > to do with the storage? Considering a seek time in the range of ~10ms > this would only be right for HZ=100 and the wait would otherwise be too > short to maximize batching within a single transaction. > I wouldn't say "right amount", more of "traditional amount". If you have super slow storage this patch will not result in you waiting any longer than you did originally, which I think is what the concern was, that we not wait a super long time just because the disk is slow. > > type threads with patch without patch > > sata 2 24.6 26.3 > > sata 4 49.2 48.1 > > sata 8 70.1 67.0 > > sata 16 104.0 94.1 > > sata 32 153.6 142.7 > > In the previous patch where this wasn't limited it had better performance > even for the 2 thread case. With the current 1-jiffie wait it likely > isn't long enough to batch every pair of operations and every other > operation waits an extra amount before giving up too soon. Previous patch: > > type threads patch unpatched > sata 2 34.6 26.2 > sata 4 58.0 48.0 > sata 8 75.2 70.4 > sata 16 101.1 89.6 > > I'd recommend changing the patch to have a maximum sleep time that has a > fixed maximum number of milliseconds (15ms should be enough for even very > old disks). > This stat gathering process has been very unscientific :), I just ran once and took that number. Sometimes the patched version would come out on top, sometimes it wouldn't. If I were to do this the way my stat teacher taught me I'm sure the patched/unpatched versions would come out to be relatively the same in the 2 thread case. > > That said, this would be a minor enhancement and should NOT be considered > a reason to delay this patch's inclusion into -mm or the ext4 tree. > > PS - it should really go into jbd2 also > Yes I will be doing a jbd2 version of this patch provided there are no issues with this patch. Thanks much for the comments, Josef -- 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
