Jens Axboe wrote: > Hi, > > Since I'll be on vacation next week, I thought I'd send this out in > case people wanted to play with it. It works here, but I haven't done > any performance numbers at all. > > Patches 1-7 are all preparation patches for #8, which contains the > real changes. I'm not particularly happy with the arch implementation > for raising a softirq on another CPU, but it should be fast enough > so suffice for testing. > > Anyway, this patchset is mainly meant as a playground for testing IO > affinity. It allows you to set three values per queue, see the files > in the /sys/block/<dev>/queue directory: > > completion_affinity > Only allow completions to happen on the defined CPU mask. > queue_affinity > Only allow queuing to happen on the defined CPU mask. > rq_affinity > Always complete a request on the same CPU that queued it. > > As you can tell, there's some overlap to allow for experimentation. > rq_affinity will override completion_affinity, so it's possible to > have completions on a CPU that isn't set in that mask. The interface > is currently limited to all CPUs or a specific CPU, but the implementation > is supports (and works with) cpu masks. The logic is in > blk_queue_set_cpumask(), it should be easy enough to change this to > echo a full mask, or allow OR'ing of CPU masks when a new CPU is passed in. > For now, echo a CPU number to set that CPU, or use -1 to set all CPUs. > The default is all CPUs for no change in behaviour. > > Patch set is against current git as of this morning. The code is also in > the block git repo, branch is io-cpu-affinity. > > git://git.kernel.dk/linux-2.6-block.git io-cpu-affinity >
FYI: on a kernel with this patch set, running on a 4-way ia64 (non-NUMA) w/ a FC disk, I crafted a test with 135 combinations: o Having the issuing application pegged on each CPU - or - left alone (run on any CPU), yields 5 possibilities o Having the queue affinity on each CPU, or any (-1), yields 5 possibilities o Having the completion affinity on each CPU, or any (-1), yields 5 possibilities and o Having the issuing application pegged on each CPU - or - left alone (run on ay CPU), yields 5 possibilities o Having rq_affinity set to 0 or 1, yields 2 possibilities. Each test was for 10 minutes, and ran overnight just fine. The difference amongst the 135 resulting values (based upon latency per-IO seen at the application layer) was <<1% (0.32% to be exact). This would seem to indicate that there isn't a penalty for running with this code, and it seems relatively stable given this. The application used was doing 64KiB asynchronous direct reads, and had a minimum average per-IO latency of 42.426310 milliseconds, and average of 42.486557 milliseconds (std dev of 0.0041561), and a max of 42.561360 milliseconds I'm going to do some runs on a 16-way NUMA box, w/ a lot of disks today, to see if we see gains in that environment. Alan D. Brunelle HP OSLO S&P -- 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/