"Chen, Kenneth W" <[EMAIL PROTECTED]> wrote: > > Andrew Morton wrote Wednesday, March 09, 2005 6:26 PM > > What does "1/3 of the total benchmark performance regression" mean? One > > third of 0.1% isn't very impressive. You haven't told us anything at all > > about the magnitude of this regression. > > 2.6.9 kernel is 6% slower compare to distributor's 2.4 kernel (RHEL3). > Roughly > 2% came from storage driver (I'm not allowed to say anything beyond that, > there > is a fix though).
The codepaths are indeed longer in 2.6. > 2% came from DIO. hm, that's not a lot. Once you redo that patch to use aops and to work with O_DIRECT, the paths will get a little deeper, but not much. We really should do this so that O_DIRECT works, and in case someone has gone and mmapped the blockdev. Fine-grained alignment is probably too hard, and it should fall back to __blockdev_direct_IO(). Does it do the right thing with a request which is non-page-aligned, but 512-byte aligned? readv and writev? 2% is pretty thin :( > The rest of 2% is still unaccounted for. We don't know where. General cache replacement, perhaps. 9MB is a big cache though. > ... > Around 2.6.5, we found global plug list is causing huge lock contention on > 32-way numa box. That got fixed in 2.6.7. Then comes 2.6.8 which took a big > dip at close to 20% regression. Then we fixed 17% regression in the scheduler > (fixed with cache_decay_tick). 2.6.9 is the last one we measured and it is 6% > slower. It's a constant moving target, a wild goose to chase. > OK. Seems that the 2.4 O(1) scheduler got it right for that machine. > haven't got a chance to run transaction processing db workload on 2.6 kernel. > Perhaps they have not compared, perhaps they are working on the same problem. > I just don't know. Maybe there are other factors which drown these little things out: architecture improvements, choice of architecture, driver changes, etc. - 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/
