On Fri, Jun 6, 2014 at 9:55 AM, Jens Axboe <ax...@kernel.dk> wrote: > On 2014-06-05 17:33, Ming Lei wrote: >> >> On Fri, Jun 6, 2014 at 1:17 AM, Jens Axboe <ax...@kernel.dk> wrote: >>> >>> On 06/05/2014 08:16 AM, Ming Lei wrote: >>>> >>>> On Thu, Jun 5, 2014 at 10:03 PM, Jens Axboe <ax...@kernel.dk> wrote: >>>>> >>>>> On 2014-06-05 08:01, Alexander Gordeev wrote: >>>>>> >>>>>> >>>>>> On Wed, Jun 04, 2014 at 08:18:42AM -0600, Jens Axboe wrote: >>>>>>> >>>>>>> >>>>>>> A null_blk test is the absolute best case for percpu_ida, since >>>>>>> there are enough tags and everything is localized. The above test is >>>>>>> more useful for testing blk-mq than any real world application of >>>>>>> the tagging. >>>>>>> >>>>>>> I've done considerable testing on both 2 and 4 socket (32 and 64 >>>>>>> CPUs) and bitmap tagging is better in a much wider range of >>>>>>> applications. This includes even high tag depth devices like nvme, >>>>>>> and more normal ranges like mtip32xx and scsi-mq setups. >>>>>> >>>>>> >>>>>> >>>>>> Just for the record: bitmap tags on a 48 CPU box with NVMe device >>>>>> indeed shows almost the same performance/cache rate as the stock >>>>>> kernel. >>>>> >>>>> >>>>> >>>>> Thanks for confirming. It's one of the dangers of null_blk, it's not >>>>> always >>>>> a very accurate simulation of what a real device will do. I think it's >>>>> mostly a completion side thing, would be great with a small device that >>>>> supported msi-x and could be used as an irq trigger :-) >>>> >>>> >>>> Maybe null_blk at IRQ_TIMER mode is more close to >>>> a real device, and I guess the result may be different with >>>> mode IRQ_NONE/IRQ_SOFTIRQ. >>> >>> >>> It'd be closer in behavior, but the results might then be skewed by >>> hitting the timer way too hard. And it'd be a general slowdown, again >>> possibly skewing it. But I haven't tried with the timer completion, to >>> see if that yields more accurate modelling for this test, so it might >>> actually be a lot better. >> >> >> My test on a 16core VM(host: 2 sockets, 16core): >> >> 1, bitmap tag allocation(3.15-rc7-next): >> - softirq mode: 759K IOPS >> - timer mode: 409K IOPS >> >> 2, percpu_ida allocation(3.15-rc7) >> - softirq mode: 1116K IOPS >> - timer mode: 411K IOPS > > > It's hard to say if this is close, or whether we are just timer bound at > that point.
You are right, my previous test should be timer bound, but it should be eased by increasing timer period. I do the test again with increasing parameter of completion_nsec to 235000 from default 10000: 1, nullblk(timer mode)3.15-rc7: - each fio cpu utilization: 80% ~ 90% - 860K IOPS 2, nullbk(timer mode)3.15-rc7-next - each fio cpu utilization: 70~80% - 940K IOPS Then bitmap based allocation can be observed to be a bit better than percpu ida. Thanks, -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
