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Re: [Qemu-devel] [PATCH v4 1/6] block: use 1 MB bounce buffers for crypt
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH v4 1/6] block: use 1 MB bounce buffers for crypto instead of 16KB |
Date: |
Wed, 27 Sep 2017 08:27:56 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 |
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 <address@hidden>
> ---
> block/crypto.c | 28 +++++++++++++++-------------
> 1 file changed, 15 insertions(+), 13 deletions(-)
Reviewed-by: Eric Blake <address@hidden>
> @@ -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 <address@hidden>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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- [Qemu-devel] [PATCH v4 0/6] Misc improvements to crypto block driver, Daniel P. Berrange, 2017/09/27
- [Qemu-devel] [PATCH v4 1/6] block: use 1 MB bounce buffers for crypto instead of 16KB, Daniel P. Berrange, 2017/09/27
- [Qemu-devel] [PATCH v4 2/6] crypto: expose encryption sector size in APIs, Daniel P. Berrange, 2017/09/27
- [Qemu-devel] [PATCH v4 3/6] block: fix data type casting for crypto payload offset, Daniel P. Berrange, 2017/09/27
- [Qemu-devel] [PATCH v4 6/6] block: support passthrough of BDRV_REQ_FUA in crypto driver, Daniel P. Berrange, 2017/09/27
- [Qemu-devel] [PATCH v4 5/6] block: convert qcrypto_block_encrypt|decrypt to take bytes offset, Daniel P. Berrange, 2017/09/27
- [Qemu-devel] [PATCH v4 4/6] block: convert crypto driver to bdrv_co_preadv|pwritev, Daniel P. Berrange, 2017/09/27