Hi Dan, On Sat, Mar 14, 2009 at 10:07:49AM -0700, Dan Williams wrote: > I am curious, can you say a bit more about the performance problems > you solved with this data? Is there a corresponding userspace tool > that interprets these numbers? With the original patch there was no need for a tool - statistics were in /proc/mdstat and were fairly easy to understand. The patch I recently submitted would need a small tool, but one has not been written. I've looked into how we've used this data in the past, and while our support team often requests /proc/mdstat from customers experiencing RAID performance problems, they rarely receive it. The original statistics patch (which has been shipping with Lustre for about 3 years) seems to have been useful for 2 things: 1. Analyzing RAID IO patterns when developing our RAID performance improvements (which seem to be completely obsolete now thanks to the more extensive improvements you and Neil have done, so I won't be submitting them.) Of course, this is now a good reason to merge the patch - if anyone (including us) wants to do similar studies, they can develop their own internal patch. 2. The out_of_stripes tracking is useful - we've found several cases where stripe_cache_size was set too low and performance suffered as a result. Monitoring stripe_cache_active during IO is difficult so it's far better to have a counter like this. So if we can solve the second problem somehow - maybe just introduce a read-only counter under /sys/block/md*/md/out_of_stripes - the need for the rest of the patch goes away IMO. > [...] > So, my original suggestion/question should have been why not extend > blktrace to understand these incremental MD events? Regarding blktrace specifically, it's really geared towards developers. I played with it a bit and it looks like it might be useful to me at some point, but I wouldn't expect a customer to use it. It would need a much better frontend tool and a more supported kernel interface than debugfs. But as I said, our customers aren't using our existing /proc/mdstat information very much anyway so I don't think this problem needs to be solved. Cheers, Jody > Regards, > Dan -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
