File block-add-max_hw_transfer-to-BlockLimits.patch of Package qemu.29315
From: Lin Ma <lma@suse.com>
Date: Mon, 13 Sep 2021 18:33:11 +0800
Subject: block: add max_hw_transfer to BlockLimits
Git-commit: 24b36e9813ec15da7db62e3b3621730710c5f020
References: bsc#1190425
For block host devices, I/O can happen through either the kernel file
descriptor I/O system calls (preadv/pwritev, io_submit, io_uring)
or the SCSI passthrough ioctl SG_IO.
In the latter case, the size of each transfer can be limited by the
HBA, while for file descriptor I/O the kernel is able to split and
merge I/O in smaller pieces as needed. Applying the HBA limits to
file descriptor I/O results in more system calls and suboptimal
performance, so this patch splits the max_transfer limit in two:
max_transfer remains valid and is used in general, while max_hw_transfer
is limited to the maximum hardware size. max_hw_transfer can then be
included by the scsi-generic driver in the block limits page, to ensure
that the stricter hardware limit is used.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Lin Ma <lma@suse.com>
---
block/block-backend.c | 13 +++++++++++++
block/file-posix.c | 2 +-
block/io.c | 2 ++
hw/scsi/scsi-generic.c | 2 +-
include/block/block_int.h | 7 +++++++
include/sysemu/block-backend.h | 1 +
6 files changed, 25 insertions(+), 2 deletions(-)
diff --git a/block/block-backend.c b/block/block-backend.c
index dfb0fd41e52372c2373ba27d62b1..6fafe601a27f13d77cbea7c78b42 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1939,6 +1939,19 @@ uint32_t blk_get_request_alignment(BlockBackend *blk)
return bs ? bs->bl.request_alignment : BDRV_SECTOR_SIZE;
}
+/* Returns the maximum hardware transfer length, in bytes; guaranteed nonzero */
+uint64_t blk_get_max_hw_transfer(BlockBackend *blk)
+{
+ BlockDriverState *bs = blk_bs(blk);
+ uint64_t max = INT_MAX;
+
+ if (bs) {
+ max = MIN_NON_ZERO(max, bs->bl.max_hw_transfer);
+ max = MIN_NON_ZERO(max, bs->bl.max_transfer);
+ }
+ return ROUND_DOWN(max, blk_get_request_alignment(blk));
+}
+
/* Returns the maximum transfer length, in bytes; guaranteed nonzero */
uint32_t blk_get_max_transfer(BlockBackend *blk)
{
diff --git a/block/file-posix.c b/block/file-posix.c
index 72a259923b4db9b133a37572b79a..649a5408195c16c38dc09d9048da 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1245,7 +1245,7 @@ static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
int ret = sg_get_max_transfer_length(s->fd);
if (ret > 0 && ret <= BDRV_REQUEST_MAX_BYTES) {
- bs->bl.max_transfer = pow2floor(ret);
+ bs->bl.max_hw_transfer = pow2floor(ret);
}
ret = sg_get_max_segments(s->fd);
diff --git a/block/io.c b/block/io.c
index a9f56a9ab1c56a3ca83833bfb0fa..28134b85c8a19ab10a4191e3b725 100644
--- a/block/io.c
+++ b/block/io.c
@@ -126,6 +126,8 @@ static void bdrv_merge_limits(BlockLimits *dst, const BlockLimits *src)
{
dst->opt_transfer = MAX(dst->opt_transfer, src->opt_transfer);
dst->max_transfer = MIN_NON_ZERO(dst->max_transfer, src->max_transfer);
+ dst->max_hw_transfer = MIN_NON_ZERO(dst->max_hw_transfer,
+ src->max_hw_transfer);
dst->opt_mem_alignment = MAX(dst->opt_mem_alignment,
src->opt_mem_alignment);
dst->min_mem_alignment = MAX(dst->min_mem_alignment,
diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
index 0cc4f9dc22edd8881da5ccddcb90..ca7f70bb1c60ab6eb7a3b64983b7 100644
--- a/hw/scsi/scsi-generic.c
+++ b/hw/scsi/scsi-generic.c
@@ -166,7 +166,7 @@ static void scsi_handle_inquiry_reply(SCSIGenericReq *r, SCSIDevice *s)
(r->req.cmd.buf[1] & 0x01)) {
page = r->req.cmd.buf[2];
if (page == 0xb0) {
- uint32_t max_transfer = blk_get_max_transfer(s->conf.blk);
+ uint64_t max_transfer = blk_get_max_hw_transfer(s->conf.blk);
uint32_t max_iov = blk_get_max_iov(s->conf.blk);
assert(max_transfer);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 95d9333be14f220f96754c3cdd73..017f2a105ad7b74194ee1aab9395 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -678,6 +678,13 @@ typedef struct BlockLimits {
* clamped down. */
uint32_t max_transfer;
+ /* Maximal hardware transfer length in bytes. Applies whenever
+ * transfers to the device bypass the kernel I/O scheduler, for
+ * example with SG_IO. If larger than max_transfer or if zero,
+ * blk_get_max_hw_transfer will fall back to max_transfer.
+ */
+ uint64_t max_hw_transfer;
+
/* memory alignment, in bytes so that no bounce buffer is needed */
size_t min_mem_alignment;
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index 880e9032930b0207e2e3e6fe1bd7..07ef7844a2da6aa05f816a1aa10c 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -204,6 +204,7 @@ void blk_eject(BlockBackend *blk, bool eject_flag);
int blk_get_flags(BlockBackend *blk);
uint32_t blk_get_request_alignment(BlockBackend *blk);
uint32_t blk_get_max_transfer(BlockBackend *blk);
+uint64_t blk_get_max_hw_transfer(BlockBackend *blk);
int blk_get_max_iov(BlockBackend *blk);
void blk_set_guest_block_size(BlockBackend *blk, int align);
void *blk_try_blockalign(BlockBackend *blk, size_t size);
