On Tue, Mar 20, 2007 at 09:08:24AM +0100, Peter Zijlstra wrote: > On Tue, 2007-03-20 at 18:47 +1100, David Chinner wrote: > > So overall we've lost about 15-20% of the theoretical aggregate > > perfomrance, but we haven't starved any of the devices over a > > long period of time. > > > > However, looking at vmstat for total throughput, there are periods > > of time where it appears that the fastest disk goes idle. That is, > > we drop from an aggregate of about 550MB/s to below 300MB/s for > > several seconds at a time. You can sort of see this from the file > > size output above - long term the ratios remain the same, but in the > > short term we see quite a bit of variability. > > I suspect you did not apply 7/6? There is some trouble with signed vs > unsigned in the initial patch set that I tried to 'fix' by masking out > the MSB, but that doesn't work and results in 'time' getting stuck for > about half the time.
I applied the fixes patch as well, so i had all that you posted... > > but it's almost > > like it is throttling a device completely while it allows another > > to finish writing it's quota (underestimating bandwidth?). > > Yeah, there is some lumpy-ness in BIO submission or write completions it > seems, and when that granularity (multiplied by the number of active > devices) is larger than the 'time' period over with we average > (indicated by vm_cycle_shift) very weird stuff can happen. Sounds like the period is a bit too short atm if we can get into this sort of problem with only 2 active devices.... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
