On 09/27/2017 07:53 AM, Daniel P. Berrange wrote: > Using 16KB bounce buffers creates a significant performance > penalty for I/O to encrypted volumes on storage which high > I/O latency (rotating rust & network drives), because it > triggers lots of fairly small I/O operations. > > On tests with rotating rust, and cache=none|directsync, > write speed increased from 2MiB/s to 32MiB/s, on a par > with that achieved by the in-kernel luks driver. With > other cache modes the in-kernel driver is still notably > faster because it is able to report completion of the > I/O request before any encryption is done, while the > in-QEMU driver must encrypt the data before completion. > > Signed-off-by: Daniel P. Berrange <berra...@redhat.com> > --- > block/crypto.c | 28 +++++++++++++++------------- > 1 file changed, 15 insertions(+), 13 deletions(-)
Reviewed-by: Eric Blake <ebl...@redhat.com> > @@ -464,12 +467,11 @@ block_crypto_co_writev(BlockDriverState *bs, int64_t > sector_num, > > qemu_iovec_init(&hd_qiov, qiov->niov); > > - /* Bounce buffer so we have a linear mem region for > - * entire sector. XXX optimize so we avoid bounce > - * buffer in case that qiov->niov == 1 > + /* Bounce buffer because we're not permitted to touch > + * contents of qiov - it points to guest memory. > */ > cipher_data = > - qemu_try_blockalign(bs->file->bs, MIN(BLOCK_CRYPTO_MAX_SECTORS * 512, > + qemu_try_blockalign(bs->file->bs, MIN(BLOCK_CRYPTO_MAX_IO_SIZE, > qiov->size)); We allocate and free a bounce buffer for every write - is there anything we can do to reduce malloc() calls by reusing a bounce buffer associated with a coroutine (we have to be careful that parallel coroutines don't share bounce buffers, of course). But that's independent of this patch. Reviewed-by: Eric Blake <ebl...@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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