Anthony Liguori wrote: > Avi Kivity wrote: >> Anthony Liguori wrote: >>> Avi Kivity wrote: >>>> Laurent Vivier wrote: >>>>> There are remaining issues : libposix-aio uses kernel AIO, so files >>>>> must be >>>>> opened using O_DIRECT and buffers must be aligned. libposix-aio is >>>>> able to >>>>> manage other cases but this has a performance cost. >>>>> >>>>> >>>> Because the guest is also doing dma, the buffers are expected to be >>>> aligned (it might be different if using pio, but unlikely). >>> The IDE emulation always uses a temporary buffer. This is partially >>> because you cannot always rely on being able to use an offset on >>> phys_ram_base (when doing user only emulation). >> Why is that? > > Well, user won't do IDE emulation, but cpu_physical_memory_rw has to > jump through more hoops for IDE. > > What's more relevant though, is it's possible for the guest to setup DMA > to device memory, in which case, you need to route the IO to callbacks. > That's pretty unlikely though so I think we can stream line it so that > we maintain correctness while also getting less copies.
I'm not sure I had understood correctly your explanation, but I tried to remove buffer from IDE device. I made a (pseudo-)benchmark with "dd" Applied patch is here: http://www.bullopensource.org/posix/qemu/ide-directio.diff (pseudo-)Benchmark is here: kvm-14 dd if=/dev/hda of=/dev/null count=100000 51200000 bytes transferred in 4.735706 seconds (10811482 bytes/sec) dd if=/dev/hda of=/dev/null count=1000000 512000000 bytes transferred in 25.218732 seconds (20302369 bytes/sec) kvm-14 + libposix-aio dd if=/dev/hda of=/dev/null count=100000 51200000 bytes transferred in 3.335737 seconds (15348932 bytes/sec) dd if=/dev/hda of=/dev/null count=1000000 512000000 bytes transferred in 19.242217 seconds (26608161 bytes/sec) kvm-14 + libposix-aio + ide-directio dd if=/dev/hda of=/dev/null count=100000 51200000 bytes transferred in 2.695296 seconds (18996058 bytes/sec) dd if=/dev/hda of=/dev/null count=1000000 512000000 bytes transferred in 14.992513 seconds (34150379 bytes/sec) qemu-0.9.0 dd if=/dev/hda of=/dev/null count=100000 1200000 bytes transferred in 2.694546 seconds (19001345 bytes/sec) dd if=/dev/hda of=/dev/null count=1000000 512000000 bytes transferred in 25.524641 seconds (20059048 bytes/sec) qemu-0.9.0 + libposix-aio dd if=/dev/hda of=/dev/null count=100000 51200000 bytes transferred in 2.859584 seconds (17904702 bytes/sec) dd if=/dev/hda of=/dev/null count=1000000 512000000 bytes transferred in 25.045071 seconds (20443144 bytes/sec) qemu-0.9.0 + libposix-aio + ide-directio dd if=/dev/hda of=/dev/null count=100000 51200000 bytes transferred in 2.897503 seconds (17670387 bytes/sec) dd if=/dev/hda of=/dev/null count=1000000 512000000 bytes transferred in 25.900654 seconds (19767841 bytes/sec) qemu-0.9.0 + kqemu dd if=/dev/hda of=/dev/null count=100000 51200000 bytes transferred in 6.204987 seconds (8251427 bytes/sec) dd if=/dev/hda of=/dev/null count=1000000 512000000 bytes transferred in 65.149972 seconds (7858791 bytes/sec) qemu-0.9.0 + kqemu + libposix-aio dd if=/dev/hda of=/dev/null count=100000 51200000 bytes transferred in 6.075537 seconds (8427239 bytes/sec) dd if=/dev/hda of=/dev/null count=1000000 512000000 bytes transferred in 57.506392 seconds (8903358 bytes/sec) qemu-0.9.0 + kqemu + libposix-aio + ide-directio dd if=/dev/hda of=/dev/null count=100000 51200000 bytes transferred in 6.083927 seconds (8415617 bytes/sec) dd if=/dev/hda of=/dev/null count=1000000 512000000 bytes transferred in 57.602499 seconds (8888503 bytes/sec) Regards, Laurent -- ------------- [EMAIL PROTECTED] -------------- "Any sufficiently advanced technology is indistinguishable from magic." - Arthur C. Clarke
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