On Tue 22-11-11 14:41:49, Wu Fengguang wrote: > On Tue, Nov 22, 2011 at 06:50:49AM +0800, Jan Kara wrote: > > On Mon 21-11-11 21:03:43, Wu Fengguang wrote: > > > Add an upper limit to balanced_rate according to the below inequality. > > > This filters out some rare but huge singular points, which at least > > > enables more readable gnuplot figures. > > > > > > When there are N dd dirtiers, > > > > > > balanced_dirty_ratelimit = write_bw / N > > > > > > So it holds that > > > > > > balanced_dirty_ratelimit <= write_bw > > The change makes sense, but do we understand why there are such huge > > singular points? Are they due to errors in estimation of bandwidth or due > > to errors in dirtying rate computations (e.g. due to truncates), or > > something else? > > Good point. I'll add this to the changelog: > > The singular points originate from dirty_rate in the below formular: > > balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate > where > dirty_rate = (number of page dirties in the past 200ms) / 200ms > > In the extreme case, if all dd tasks suddenly get blocked on something > else and hence no pages are dirtied at all, dirty_rate will be 0 and > balanced_dirty_ratelimit will be inf. This could happen in reality. > > There won't be tiny singular points though, as long as the dirty pages > lie inside the dirty control area (above the freerun region). > Because there the dd tasks will be throttled by balanced_dirty_pages() > and won't be able to suddenly dirty much more pages than average. OK, I see. Thanks for explanation. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
