Chen, Kenneth W wrote on Wednesday, March 09, 2005 5:45 PM > Andrew Morton wrote on Wednesday, March 09, 2005 5:34 PM > > What are these percentages? Total CPU time? The direct-io stuff doesn't > > look too bad. It's surprising that tweaking the direct-io submission code > > makes much difference. > > Percentage is relative to total kernel time. There are three DIO functions > showed up in the profile: > > __blockdev_direct_IO 4.97% > dio_bio_end_io 2.70% > dio_bio_complete 1.20%
For the sake of comparison, let's look at the effect of performance patch on raw device, in place of the above three functions, we now have two: raw_file_rw 1.59% raw_file_aio_rw 1.19% A total saving of 6.09% (4.97+2.70+1.20 -1.59-1.19). That's only counting the cpu cycles. We have tons of other data showing significant kernel path length reduction with the performance patch. Cache misses reduced across the entire 3 level cache hierarchy, that's a secondary effect can not be ignored since kernel is also competing cache resource with application. - Ken - 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/
