On 01/12/22 15:04, Nir Soffer wrote: > On Wed, Jan 12, 2022 at 1:12 PM Laszlo Ersek <[email protected]> wrote: >> >> On 01/11/22 11:56, Richard W.M. Jones wrote: >>> On Tue, Jan 11, 2022 at 08:07:39AM +0100, Laszlo Ersek wrote: >>>> hmmmm, not necessarily; according to the manual, "qemu-img convert" uses >>>> (by default) 8 co-routines. There's also the -W flag ("out of order >>>> writes"), which I don't know if the original virt-v2v used. >>> >>> I'm never sure how qemu coroutines map to threads. I assume it's not >>> 1-1, and it's somehow connected to the iothread setting? >> >> (I don't know the answer, but) this difference should not matter here I >> believe; the QEMU co-routines submit async IO one way or another (IIRC), >> so once those are in the kernel's hands, it shouldn't matter (from an IO >> performance perspective) whether the userspace process waits on their >> completions with heavy-weight threads, or co-routines or whatever. What >> matters is that the kernel has multiple IO reqs in flight at the same time. > > In practice this matters a lot. Using -W can be 6x times faster with qemu-img > convert. > > See how I tested this here: > https://bugzilla.redhat.com/1511891#c57
Sorry, I didn't mean the difference between "-W" and "no -W". I meant the difference between "NPTL threads submitting async IO requests" and "coroutines submitting async IO requests". Thanks Laszlo _______________________________________________ Libguestfs mailing list [email protected] https://listman.redhat.com/mailman/listinfo/libguestfs
