Jens Axboe wrote:
I just wish you had a rationale behind them, I don't think it's that great of a series. I agree with the low point of 128k. Then it'd be sane to try and determine what the upper limit of ra window size goodness is, which is probably impossible since it depends on the hardware a lot. But lets just say the upper value is 2mb, then I think it's pretty silly _not_ to use 2mb on a 1g machine for instance. So more aggressive scaling.
1 or 2 MB is a nice number. Seek time (plus rotational latency) on disks still takes on the order of 10 ms, while disks commonly transfer data on the order of 50MB/second. That means one disk seek (10ms) takes as long as it takes to read around 512kB of data. The current 128kB means that if you have lots of streaming IO going on, you spend only 20% of the time transferring data and get roughly 10MB/s. Seek 10ms, read 2.5ms worth of data. OTOH, if you do 2MB per request for the same heavy streaming workload (say, an ftp or nfs server doing media files), you can get 80% of the disk throughput, or 40MB/s. This is because you spend 40ms transferring data for every 10ms seek time. Yes, filesystem metadata will reduce this "occasionally", but the general idea holds. -- Politics is the struggle between those who want to make their country the best in the world, and those who believe it already is. Each group calls the other unpatriotic. - 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/
