diff options
| author | Daniel P. Berrange <berrange@redhat.com> | 2017-09-27 13:53:35 +0100 |
|---|---|---|
| committer | Max Reitz <mreitz@redhat.com> | 2017-10-06 16:30:47 +0200 |
| commit | 161253e2d0a83a1b33bca019c6e926013e1a03db (patch) | |
| tree | 607d4598e3b8b2183726c2463aeed40352e24e60 /block/crypto.c | |
| parent | 461743390d3a1ceafa4503811adbc87c7d372741 (diff) | |
| download | qemu-161253e2d0a83a1b33bca019c6e926013e1a03db.tar.gz | |
block: use 1 MB bounce buffers for crypto instead of 16KB
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 <berrange@redhat.com>
Message-id: 20170927125340.12360-2-berrange@redhat.com
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Diffstat (limited to 'block/crypto.c')
| -rw-r--r-- | block/crypto.c | 28 |
1 files changed, 15 insertions, 13 deletions
diff --git a/block/crypto.c b/block/crypto.c index 58ef6f2f52..684cabeaf8 100644 --- a/block/crypto.c +++ b/block/crypto.c @@ -379,7 +379,11 @@ static void block_crypto_close(BlockDriverState *bs) } -#define BLOCK_CRYPTO_MAX_SECTORS 32 +/* + * 1 MB bounce buffer gives good performance / memory tradeoff + * when using cache=none|directsync. + */ +#define BLOCK_CRYPTO_MAX_IO_SIZE (1024 * 1024) static coroutine_fn int block_crypto_co_readv(BlockDriverState *bs, int64_t sector_num, @@ -396,12 +400,11 @@ block_crypto_co_readv(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 don't wish to expose cipher text + * in qiov which 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)); if (cipher_data == NULL) { ret = -ENOMEM; @@ -411,8 +414,8 @@ block_crypto_co_readv(BlockDriverState *bs, int64_t sector_num, while (remaining_sectors) { cur_nr_sectors = remaining_sectors; - if (cur_nr_sectors > BLOCK_CRYPTO_MAX_SECTORS) { - cur_nr_sectors = BLOCK_CRYPTO_MAX_SECTORS; + if (cur_nr_sectors > (BLOCK_CRYPTO_MAX_IO_SIZE / 512)) { + cur_nr_sectors = (BLOCK_CRYPTO_MAX_IO_SIZE / 512); } qemu_iovec_reset(&hd_qiov); @@ -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)); if (cipher_data == NULL) { ret = -ENOMEM; @@ -479,8 +481,8 @@ block_crypto_co_writev(BlockDriverState *bs, int64_t sector_num, while (remaining_sectors) { cur_nr_sectors = remaining_sectors; - if (cur_nr_sectors > BLOCK_CRYPTO_MAX_SECTORS) { - cur_nr_sectors = BLOCK_CRYPTO_MAX_SECTORS; + if (cur_nr_sectors > (BLOCK_CRYPTO_MAX_IO_SIZE / 512)) { + cur_nr_sectors = (BLOCK_CRYPTO_MAX_IO_SIZE / 512); } qemu_iovec_to_buf(qiov, bytes_done, |