On Thursday, October 27, 2016 8:13:08 PM CEST Ulf Hansson wrote: > On 27 October 2016 at 19:43, Jens Axboe <axboe@xxxxxxxxx> wrote: > > On 10/27/2016 11:32 AM, Ulf Hansson wrote: > >> > >> [...] > >> > >>> > >>> I'm hesistant to add a new scheduler because it's very easy to add, very > >>> difficult to get rid of. If we do add BFQ as a legacy scheduler now, > >>> it'll take us years and years to get rid of it again. We should be > >>> moving towards LESS moving parts in the legacy path, not more. > >> > >> > >> Jens, I think you are wrong here and let me try to elaborate on why. > >> > >> 1) > >> We already have legacy schedulers like CFQ, DEADLINE, etc - and most > >> block device drivers are still using the legacy blk interface. > > > > > > I don't think that's an accurate statement. In terms of coverage, most > > drivers do support blk-mq. Anything SCSI, nvme, virtio-blk, SATA runs on > > (or can run on) top of blk-mq. > > Well, I just used "git grep" and found that many drivers didn't use > blkmq. Apologize if I gave the wrong impressions. To clarify, this seems to be a complete list: $ git grep -wl '\(__\|\)blk_\(fetch\|end\|start\)_request' | xargs grep -L blk_mq Documentation/scsi/scsi_eh.txt arch/um/drivers/ubd_kern.c block/blk-tag.c block/bsg-lib.c drivers/block/DAC960.c drivers/block/amiflop.c drivers/block/aoe/aoeblk.c drivers/block/aoe/aoecmd.c drivers/block/aoe/aoedev.c drivers/block/ataflop.c drivers/block/cciss.c drivers/block/floppy.c drivers/block/hd.c drivers/block/mg_disk.c drivers/block/osdblk.c drivers/block/paride/pcd.c drivers/block/paride/pd.c drivers/block/paride/pf.c drivers/block/ps3disk.c drivers/block/skd_main.c drivers/block/sunvdc.c drivers/block/swim.c drivers/block/swim3.c drivers/block/sx8.c drivers/block/xsysace.c drivers/block/z2ram.c drivers/cdrom/gdrom.c drivers/ide/ide-atapi.c drivers/ide/ide-io.c drivers/ide/ide-pm.c drivers/memstick/core/ms_block.c drivers/memstick/core/mspro_block.c drivers/mmc/card/block.c drivers/mmc/card/queue.c drivers/mtd/mtd_blkdevs.c drivers/s390/block/dasd.c drivers/s390/block/scm_blk.c drivers/sbus/char/jsflash.c drivers/scsi/osd/osd_initiator.c drivers/scsi/scsi_transport_fc.c drivers/scsi/scsi_transport_sas.c samples/bpf/tracex3_kern.c >From what I can tell, most of these are hopelessly obsolete, but there are some notable exceptions: aoe, osdblk, skd, sunvdc, mtdblk, mmc, dasd and scm. I've never used any of the first four, but the last four of the list are certainly important (for very different reasons). Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
