Am Sun, 9 Oct 2016 06:25:20 -0700 schrieb Grant <emailgr...@gmail.com>:
> > Looking at the times, it looks a lot like you are having higher > > iowait only at around 2:00 and 4:20 which are pretty standard cron > > job times. These probably run niced or ioniced. It's normal that > > you are seeing higher iowait for such processes. > > > > You may want to try setting your io scheduler to deadline (or even > > noop if you are using a RAID controller with bbu and write cache). > > Since you seem to prefer response times over throughput you should > > be using deadline io scheduler anyways. Actually, don't use the > > default CFQ if your server is virtualized. At least in my tests, > > CFQ seems to work a lot against what virtualized IO seems to > > achieve. > > > I'm using CFQ now, no virtualization. I should use CFQ if I prefer > throughput and deadline for response time? Maybe not as easy as that. But I remember benchmarks found that deadline or noop may give better web server performance. But that depends on your application. I'm running a few virtual machines concurrently on a few less hardware machines. Resources are sometimes a bit overcommitted, and I see deadline gives much reduced iowait in the machines in contrast to using cfq. > > I also suggest using maybe XFS as a filesystem. Which one are you > > using? > > > I'm using ext3 but I plan to move to ZFS. XFS is much better at handling many parallel requests, and is also quite good working with deadline. I strongly suggest against using ZFS if swapping is already a problem for you even now. > > If your server is a web server and it starts swapping, there is not > > much you can do against it. Tuning swappiness will probably not > > help at all. Get more RAM or lower your memory usage. If, for > > example, MySQL runs on the same host, either move it or lower it's > > memory usage. Reduce the amount of apache application processes > > running at the same time (PHP, Perl, whatever), use a layered > > application stack: One frontend for handling static files, one > > middleware server for handling requests over to PHP and doing the > > request dispatch queue, and reduce memory/IO footprint of your > > backend. > > Changing swappiness from 60 to 30 has drastically reduced swap usage > but I'm not sure how much it has done for iowait and response times. > I'll know more in a few days. If swap usage stays very low and I'm > still not happy with the consistency of response times, I would think > reducing memory usage won't help. Yes, it may have reduced swap usage - but at what price? Reduced cache? This can only increase iowait... -- Regards, Kai Replies to list-only preferred.
