On Thu, Jun 26, 2014 at 12:50:32PM -0400, Jeff Moyer wrote: > Mel Gorman <mgorman@xxxxxxx> writes: > > > On Thu, Jun 26, 2014 at 11:36:50AM -0400, Jeff Moyer wrote: > >> Right, and I guess I hadn't considered that case as I thought folks used > >> more than one spinning disk for such workloads. > >> > > > > They probably are but by and large my IO testing is based on simple > > storage. The reasoning is that if we get the simple case wrong then we > > probably are getting the complex case wrong too or at least not performing > > as well as we should. I also don't use SSD on my own machines for the > > same reason. > > A single disk is actually the hard case in this instance, but I > understand what you're saying. ;-) > > >> My main reservation about this change is that you've only provided > >> numbers for one benchmark. > > > > The other obvious one to run would be pgbench workloads but it's a rathole of > > arguing whether the configuration is valid and whether it's inappropriate > > to test on simple storage. The tiobench tests alone take a long time to > > complete -- 1.5 hours on a simple machine, 7 hours on a low-end NUMA machine. > > And we should probably run our standard set of I/O exercisers at the > very least. But, like I said, it seems like wasted effort. > Out of curiousity, what do you consider to be the standard set of I/O exercisers? I have a whole battery of them that are run against major releases to track performance over time -- tiobench (it's stupid, but too many people use it), fsmark used in various configurations (single/multi threaded, zero-sized and large files), postmark (file sizes fairly small, working set 2xRAM), bonnie++ (2xRAM), ffsb used in a mail server configuration (taken from btrfs tests), dbench3 (checking in-memory updates, not a realistic IO benchmark), dbench4 (bit more realistic although high thread counts it gets silly and overall it's not a stable predictor of performance), sysbench in various configurations, pgbench used in limited configurations, stutter which tends to hit the worse-case interactivity issues experienced on desktops and kernel builds are the main ones. It takes days to churn through the full set of tests which is why I don't do it for a patch series. I selected tiobench this time because it was the most reliable test to cover both single and multiple-sources-of-IO cases. If I merge a major change I'll usually then watch the next major release and double check that nothing else broke. > >> To bump the default target_latency, ideally > >> we'd know how it affects other workloads. However, I'm having a hard > >> time justifying putting any time into this for a couple of reasons: > >> 1) blk-mq pretty much does away with the i/o scheduler, and that is the > >> future > >> 2) there is work in progress to convert cfq into bfq, and that will > >> essentially make any effort put into this irrelevant (so it might be > >> interesting to test your workload with bfq) > >> > > > > Ok, you've convinced me and I'll drop this patch. For anyone based on > > kernels from around this time they can tune CFQ or buy a better disk. > > Hopefully they will find this via Google. > > Funny, I wasn't weighing in against your patch. I was merely indicating > that I personally wasn't going to invest the time to validate it. But, > if you're ok with dropping it, that's obviously fine with me. > I fear the writing is on the wall that it'll never pass the "have you tested every workload" test and no matter what a counter-example will be found where it's the wrong setting. If CFQ is going to be irrelevant soon it's just not worth wasting the electricity against a mainline kernel. I'm still interested in what you consider your standard set of IO exercisers though because I can slot any missing parts into the tests that run for every mainline release. The main one I'm missing is the postgres folks fsync benchmark. I wrote the automation months ago but never activated it because there are enough known problems already. Thanks. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>