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. 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/
