On Thu, Feb 14 2019 at 10:00am -0500, Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > This patch improves performance of dm-linear and dm-striped targets. > Device mapper copies the whole bio and passes it to the lower layer. This > copying may be avoided in special cases. > > This patch changes the logic so that instead of copying the bio we > allocate a structure dm_noclone (it has only 4 entries), save the values > bi_end_io and bi_private in it, overwrite these values in the bio and pass > the bio to the lower block device. > > When the bio is finished, the function noclone_endio restores te values > bi_end_io and bi_private and passes the bio to the original bi_end_io > function. > > This optimization can only be done by dm-linear and dm-striped targets, > the target can op-in by setting ti->no_clone = true. > > Performance improvement: > > # modprobe brd rd_size=1048576 > # dd if=/dev/zero of=/dev/ram0 bs=1M oflag=direct > # dmsetup create lin --table "0 2097152 linear /dev/ram0 0" > # fio --ioengine=psync --iodepth=1 --rw=read --bs=512 --direct=1 --numjobs=12 --time_based --runtime=10 --group_reporting --name=/dev/mapper/lin > > x86-64, 2x six-core > /dev/ram0 2449MiB/s > /dev/mapper/lin 5.0-rc without optimization 1970MiB/s > /dev/mapper/lin 5.0-rc with optimization 2238MiB/s > > arm64, quad core: > /dev/ram0 457MiB/s > /dev/mapper/lin 5.0-rc without optimization 325MiB/s > /dev/mapper/lin 5.0-rc with optimization 364MiB/s > > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> Nice performance improvement. But each device should have its own mempool for dm_noclone + front padding. So it should be wired into dm_alloc_md_mempools(). It is fine if you don't actually deal with supporting per-bio-data in this patch, but a follow-on patch to add support for noclone-based per-bio-data shouldn't be expected to refactor the location of the mempool allocation (module vs per-device granularity). Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
