On 2021/04/09 23:47, Bart Van Assche wrote: > On 4/7/21 3:27 AM, Damien Le Moal wrote: >> On 2021/04/07 18:46, Changheun Lee wrote: >>> I'll prepare new patch as you recommand. It will be added setting of >>> limit_bio_size automatically when queue max sectors is determined. >> >> Please do that in the driver for the HW that benefits from it. Do not do this >> for all block devices. > > Hmm ... is it ever useful to build a bio with a size that exceeds > max_hw_sectors when submitting a bio directly to a block device, or in > other words, if no stacked block driver sits between the submitter and > the block device? Am I perhaps missing something?
Device performance wise, the benefits are certainly not obvious to me either. But for very fast block devices, I think the CPU overhead of building more smaller BIOs may be significant compared to splitting a large BIO into multiple requests. Though it may be good to revisit this with some benchmark numbers. > > Thanks, > > Bart. > -- Damien Le Moal Western Digital Research
