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From 16e6d181f5e881082a42dbae18c8f002fbbe689a Mon Sep 17 00:00:00 2001
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From: "Daniel P. Berrange" <berrange@redhat.com>
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Date: Fri, 1 Dec 2017 10:44:46 +0100
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Subject: [PATCH 10/36] block: use 1 MB bounce buffers for crypto instead of
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16KB
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RH-Author: Daniel P. Berrange <berrange@redhat.com>
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Message-id: <20171201104446.7973-1-berrange@redhat.com>
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Patchwork-id: 78063
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O-Subject: [RHV-7.5 qemu-kvm-rhev PATCH] block: use 1 MB bounce buffers for crypto instead of 16KB
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Bugzilla: 1500334
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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RH-Acked-by: Jeffrey Cody <jcody@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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Using 16KB bounce buffers creates a significant performance
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penalty for I/O to encrypted volumes on storage which high
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I/O latency (rotating rust & network drives), because it
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triggers lots of fairly small I/O operations.
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On tests with rotating rust, and cache=none|directsync,
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write speed increased from 2MiB/s to 32MiB/s, on a par
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with that achieved by the in-kernel luks driver. With
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other cache modes the in-kernel driver is still notably
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faster because it is able to report completion of the
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I/O request before any encryption is done, while the
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in-QEMU driver must encrypt the data before completion.
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Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
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Message-id: 20170927125340.12360-2-berrange@redhat.com
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Reviewed-by: Eric Blake <eblake@redhat.com>
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Reviewed-by: Max Reitz <mreitz@redhat.com>
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Signed-off-by: Max Reitz <mreitz@redhat.com>
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(cherry picked from commit 161253e2d0a83a1b33bca019c6e926013e1a03db)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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block/crypto.c | 28 +++++++++++++++-------------
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1 file changed, 15 insertions(+), 13 deletions(-)
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diff --git a/block/crypto.c b/block/crypto.c
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index 58ef6f2..684cabe 100644
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--- a/block/crypto.c
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+++ b/block/crypto.c
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@@ -379,7 +379,11 @@ static void block_crypto_close(BlockDriverState *bs)
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}
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-#define BLOCK_CRYPTO_MAX_SECTORS 32
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+/*
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+ * 1 MB bounce buffer gives good performance / memory tradeoff
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+ * when using cache=none|directsync.
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+ */
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+#define BLOCK_CRYPTO_MAX_IO_SIZE (1024 * 1024)
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static coroutine_fn int
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block_crypto_co_readv(BlockDriverState *bs, int64_t sector_num,
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@@ -396,12 +400,11 @@ block_crypto_co_readv(BlockDriverState *bs, int64_t sector_num,
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qemu_iovec_init(&hd_qiov, qiov->niov);
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- /* Bounce buffer so we have a linear mem region for
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- * entire sector. XXX optimize so we avoid bounce
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- * buffer in case that qiov->niov == 1
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+ /* Bounce buffer because we don't wish to expose cipher text
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+ * in qiov which points to guest memory.
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*/
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cipher_data =
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- qemu_try_blockalign(bs->file->bs, MIN(BLOCK_CRYPTO_MAX_SECTORS * 512,
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+ qemu_try_blockalign(bs->file->bs, MIN(BLOCK_CRYPTO_MAX_IO_SIZE,
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qiov->size));
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if (cipher_data == NULL) {
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ret = -ENOMEM;
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@@ -411,8 +414,8 @@ block_crypto_co_readv(BlockDriverState *bs, int64_t sector_num,
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while (remaining_sectors) {
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cur_nr_sectors = remaining_sectors;
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- if (cur_nr_sectors > BLOCK_CRYPTO_MAX_SECTORS) {
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- cur_nr_sectors = BLOCK_CRYPTO_MAX_SECTORS;
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+ if (cur_nr_sectors > (BLOCK_CRYPTO_MAX_IO_SIZE / 512)) {
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+ cur_nr_sectors = (BLOCK_CRYPTO_MAX_IO_SIZE / 512);
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}
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qemu_iovec_reset(&hd_qiov);
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@@ -464,12 +467,11 @@ block_crypto_co_writev(BlockDriverState *bs, int64_t sector_num,
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qemu_iovec_init(&hd_qiov, qiov->niov);
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- /* Bounce buffer so we have a linear mem region for
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- * entire sector. XXX optimize so we avoid bounce
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- * buffer in case that qiov->niov == 1
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+ /* Bounce buffer because we're not permitted to touch
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+ * contents of qiov - it points to guest memory.
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*/
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cipher_data =
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- qemu_try_blockalign(bs->file->bs, MIN(BLOCK_CRYPTO_MAX_SECTORS * 512,
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+ qemu_try_blockalign(bs->file->bs, MIN(BLOCK_CRYPTO_MAX_IO_SIZE,
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qiov->size));
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if (cipher_data == NULL) {
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ret = -ENOMEM;
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@@ -479,8 +481,8 @@ block_crypto_co_writev(BlockDriverState *bs, int64_t sector_num,
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while (remaining_sectors) {
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cur_nr_sectors = remaining_sectors;
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- if (cur_nr_sectors > BLOCK_CRYPTO_MAX_SECTORS) {
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- cur_nr_sectors = BLOCK_CRYPTO_MAX_SECTORS;
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+ if (cur_nr_sectors > (BLOCK_CRYPTO_MAX_IO_SIZE / 512)) {
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+ cur_nr_sectors = (BLOCK_CRYPTO_MAX_IO_SIZE / 512);
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}
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qemu_iovec_to_buf(qiov, bytes_done,
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--
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1.8.3.1
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