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[Qemu-block] [PATCH v2 1/4] block: use 1 MB bounce buffers for crypto in
From: |
Daniel P. Berrange |
Subject: |
[Qemu-block] [PATCH v2 1/4] block: use 1 MB bounce buffers for crypto instead of 16KB |
Date: |
Thu, 31 Aug 2017 12:05:15 +0100 |
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.
Reviewed-by: Eric Blake <address@hidden>
Reviewed-by: Stefan Hajnoczi <address@hidden>
Signed-off-by: Daniel P. Berrange <address@hidden>
---
block/crypto.c | 12 +++++-------
1 file changed, 5 insertions(+), 7 deletions(-)
diff --git a/block/crypto.c b/block/crypto.c
index 58ef6f2f52..cc8afe0e0d 100644
--- a/block/crypto.c
+++ b/block/crypto.c
@@ -379,7 +379,7 @@ static void block_crypto_close(BlockDriverState *bs)
}
-#define BLOCK_CRYPTO_MAX_SECTORS 32
+#define BLOCK_CRYPTO_MAX_SECTORS 2048
static coroutine_fn int
block_crypto_co_readv(BlockDriverState *bs, int64_t sector_num,
@@ -396,9 +396,8 @@ 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,
@@ -464,9 +463,8 @@ 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,
--
2.13.5