Am 04.07.2019 um 14:43 hat Maxim Levitsky geschrieben: > Linux block devices, even in O_DIRECT mode don't have any user visible > limit on transfer size / number of segments, which underlying kernel block > device can have. > The kernel block layer takes care of enforcing these limits by splitting the > bios. > > By limiting the transfer sizes, we force qemu to do the splitting itself which > introduces various overheads. > It is especially visible in nbd server, where the low max transfer size of the > underlying device forces us to advertise this over NBD, thus increasing the > traffic overhead in case of image conversion which benefits from large blocks. > > More information can be found here: > https://bugzilla.redhat.com/show_bug.cgi?id=1647104 > > Tested this with qemu-img convert over nbd and natively and to my surprise, > even native IO performance improved a bit.
Thanks, applied to the block branch. Kevin
