Hi Stefan, thanks for the review. I took note of your comments.
On Thu, 2022-02-03 at 10:53 +0000, Stefan Hajnoczi wrote:
> > Some background on my workload: I'm using IDE emulation, the guest is an
> > old RTOS that doesn't support virtio, using 'aio=native' isn't possible
> > either (unaligned IO accesses).
>
> I thought QEMU's block layer creates bounce buffers for unaligned
> accesses, handling both memory buffer alignment and LBA alignment
> necessary for aio=native,cache=none?
See block/file-posix.c:raw_co_prw() {
/*
* When using O_DIRECT, the request must be aligned to be able to use
* either libaio or io_uring interface. If not fail back to regular thread
* pool read/write code which emulates this for us if we set
* QEMU_AIO_MISALIGNED.
*/
if (s->needs_alignment && !bdrv_qiov_is_aligned(bs, qiov))
type |= QEMU_AIO_MISALIGNED;
else if (s->use_linux_io_uring)
return luring_co_submit(...);
else if (s->use_linux_aio)
return laio_co_submit(...);
return raw_thread_pool_submit(..., handle_aiocb_rw, ...);
}
bdrv_qiov_is_aligned() returns 'false' on my use-case.
I believe what you're referring to happens in handle_aiocb_rw(), but it's too
late then.
Thanks,
--
Nicolás Sáenz
