On Wed, 22 Aug 2012 13:47:07 -0700 Dan Williams <djbw@xxxxxx> wrote: > On Tue, Aug 21, 2012 at 11:00 PM, NeilBrown <neilb@xxxxxxx> wrote: > > On Wed, 22 Aug 2012 11:57:02 +0800 Yuanhan Liu <yuanhan.liu@xxxxxxxxxxxxxxx> > > wrote: > > > >> > >> -#define NR_STRIPES 256 > >> +#define NR_STRIPES 1024 > > > > Changing one magic number into another magic number might help your case, but > > it not really a general solution. > > > > Possibly making sure that max_nr_stripes is at least some multiple of the > > chunk size might make sense, but I wouldn't want to see a very large multiple. > > > > I thing the problems with RAID5 are deeper than that. Hopefully I'll figure > > out exactly what the best fix is soon - I'm trying to look into it. > > > > I don't think the size of the cache is a big part of the solution. I think > > correct scheduling of IO is the real answer. > > Not sure if this is what we are seeing here, but we still have the > unresolved fast parity effect whereby slower parity calculation gives > a larger time to coalesce writes. I saw this effect when playing with > xor offload. I did find a case where inserting a printk made it go faster again. Replacing that with msleep(2) worked as well. :-) I'm looking for a most robust solution though. Thanks for the reminder. NeilBrown
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