On Sun, Oct 09, 2005 at 12:19:57AM +0200, Martijn van Oosterhout wrote: > > It would be reasonable to check results in fully-cached cases, which > > would be the best real-world scenario for this to show any improvement > > in. > > If you look, I did that and even then it simply didn't make a > difference. lseek is 10 microseconds, you'd need to do hundreds of > thousands of them to make a difference. And any gain would disappear in > just the rotational latency of a hard disk read.
Just to clarify, I reexamined this point and there is a small difference. The fully cached case went from 72 seconds to 70 over 890,000 (p)read syscalls, indicating that in that case lseek/read is slower than pread by about 2 microseconds per call. The overall benefit is about 2.5%. This doesn't change the fact that any disk access at all renders the benefit almost nil. On Linux anyway, other OSes, who knows? Have a nice day, -- Martijn van Oosterhout <email@example.com> http://svana.org/kleptog/ > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a > tool for doing 5% of the work and then sitting around waiting for someone > else to do the other 95% so you can sue them.
Description: PGP signature