On 09/15/2016 11:01 AM, Ryan Stiles wrote:
Good day, We have automation that uses the "bssplit" function to get a wide variety of IO patterns, I have noticed that in 2.13 (compiled with no-shared-mem). The bsssplit only takes the first variable, meaning: bssplit=1k/50:128k/50 will yield a 100% 1k workload. This is the workload: [global] random_generator=tausworthe64 direct=1 loops=1 ioengine=libaio iodepth=16 group_reporting filename=/dev/disk/by-uuid/27602b49-4a18-4dca-a896-e2fc86746015 [workload] rw=randread bssplit=1k/50:128k/50
What's causing this issue is the use of the 64-bit random generator. There's a bug in the bssplit calculation code that overflows for that case. I've pushed a fix out for it: http://git.kernel.dk/cgit/fio/commit/?id=3dd29f7c21538c164fcbd078c3f2e532a9193a04 With that fix, you should see better behavior. Note that to truly have a 50/50 split for this, you'd want to set 'norandommap' as well. Otherwise fio will fit the block size to avoid overlapped IO. When that happens, you'll have 50% 1k random reads, but the other 50% will be between 1k and 128k. If a 128k random read would overlap at the generated offset, fio would adjust it down. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
