On 2/6/24 10:25, Bart Van Assche wrote: > On 2/5/24 16:07, Damien Le Moal wrote: >> On 2/6/24 03:18, Bart Van Assche wrote: >>> Are there numbers available about the performance differences (bandwidth >>> and latency) between plugging zoned write bios and zoned write plugging >>> requests? >> >> Finish reading the cover letter. It has lots of measurements with rc2, Jens >> block/for-next and ZWP... > Hmm ... as far as I know nobody ever implemented zoned write plugging > for requests in the block layer core so these numbers can't be in the > cover letter. No, I have not implemented zone write plugging for requests as I beleive it would lead to very similar results as zone write locking, that is, a potential problem with efficiently using a device in a mixed read/write workload as having too many plugged writes can lead to read starvation (blocking of read submission on request allocation when nr_requests is reached). > Has the bio plugging approach perhaps been chosen because it works > better for bio-based device mapper drivers? Not that it "works better" but rather that doing plugging at the BIO level allows re-using the exact same code for zone append emulation, and write ordering (if a DM driver wants the block layer to handle that). We had zone append emulation implemented for DM (for dm-crypt) using BIOs and in scsi sd driver using requests. ZWP unifies all this and will trivially allow enabling that emulation for other device types as well (e.g. NVMe ZNS drives that do not have native zone append support). -- Damien Le Moal Western Digital Research
