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authorDaniel P. Berrange <berrange@redhat.com>2017-09-27 13:53:35 +0100
committerMax Reitz <mreitz@redhat.com>2017-10-06 16:30:47 +0200
commit161253e2d0a83a1b33bca019c6e926013e1a03db (patch)
tree607d4598e3b8b2183726c2463aeed40352e24e60 /block/crypto.c
parent461743390d3a1ceafa4503811adbc87c7d372741 (diff)
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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.c28
1 files changed, 15 insertions, 13 deletions
diff --git a/block/crypto.c b/block/crypto.c
index 58ef6f2..684cabe 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,