Re: [PATCH v3 3/7] block: add max_hw_transfer to BlockLimits
On 16.06.21 15:18, Paolo Bonzini wrote:
On 15/06/21 18:18, Max Reitz wrote:
}
+/* 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(bs->bl.max_hw_transfer,
bs->bl.max_transfer);
+ }
+ return max;
Both `max_hw_transfer` and `max_transfer` can be 0, so this could
return 0, contrary to what the comment above promises.
Should `max` be initialized to 0 with a `MIN_NON_ZERO(max, INT_MAX)`
here (like `blk_get_max_transfer()` does it)?
Yes, something to that effect.
(As for the rest, I think aligning to the request alignment makes
sense, but then again we don’t do that for max_transfer either, so...
this at least wouldn’t be a new bug.
Ok, will do. I will also add a new patch to align max_transfer to the
request alignment.
Regarding the comment, checkpatch complains about it, so it should be
fixed so that /* is on its own line.
That makes it different from every other comment in block_int.h
though. Is it okay to fix all of them in a follow-up?
The reason it’s different is that the comment style in question was
added to checkpatch only relatively recently. I can’t speak for others,
but I’m a simple person. I just do what makes checkpatch happy. :)
Given that the checkpatch complaint is only a warning, I think it’s OK
to keep the comment as it is here, and perhaps optionally fix all
comments in block_int.h in a follow-up. I don’t think we need to fix
existing comments, but, well, it wouldn’t be wrong.
Max
Re: [PATCH v3 3/7] block: add max_hw_transfer to BlockLimits
On 15/06/21 18:18, Max Reitz wrote:
}
+/* 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(bs->bl.max_hw_transfer, bs->bl.max_transfer);
+ }
+ return max;
Both `max_hw_transfer` and `max_transfer` can be 0, so this could return
0, contrary to what the comment above promises.
Should `max` be initialized to 0 with a `MIN_NON_ZERO(max, INT_MAX)`
here (like `blk_get_max_transfer()` does it)?
Yes, something to that effect.
(As for the rest, I think aligning to the request alignment makes sense,
but then again we don’t do that for max_transfer either, so... this at
least wouldn’t be a new bug.
Ok, will do. I will also add a new patch to align max_transfer to the
request alignment.
Regarding the comment, checkpatch complains about it, so it should be
fixed so that /* is on its own line.
That makes it different from every other comment in block_int.h though.
Is it okay to fix all of them in a follow-up?
Paolo
Speaking of checkpatch, now that I ran it, it also complains about the
new line in bdrv_merge_limits() exceeding 80 characters, so that should
be fixed, too.)
Re: [PATCH v3 3/7] block: add max_hw_transfer to BlockLimits
On 03.06.21 15:37, Paolo Bonzini wrote:
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
---
block/block-backend.c | 12
block/file-posix.c | 2 +-
block/io.c | 1 +
hw/scsi/scsi-generic.c | 2 +-
include/block/block_int.h | 7 +++
include/sysemu/block-backend.h | 1 +
6 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/block/block-backend.c b/block/block-backend.c
index 15f1ea4288..2ea1412a54 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1953,6 +1953,18 @@ 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(bs->bl.max_hw_transfer, bs->bl.max_transfer);
+}
+return max;
Both `max_hw_transfer` and `max_transfer` can be 0, so this could return
0, contrary to what the comment above promises.
Should `max` be initialized to 0 with a `MIN_NON_ZERO(max, INT_MAX)`
here (like `blk_get_max_transfer()` does it)?
(As for the rest, I think aligning to the request alignment makes sense,
but then again we don’t do that for max_transfer either, so... this at
least wouldn’t be a new bug.
Regarding the comment, checkpatch complains about it, so it should be
fixed so that /* is on its own line.
Speaking of checkpatch, now that I ran it, it also complains about the
new line in bdrv_merge_limits() exceeding 80 characters, so that should
be fixed, too.)
Max
Re: [PATCH v3 3/7] block: add max_hw_transfer to BlockLimits
On 03/06/21 19:33, Eric Blake wrote:
+/* 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;
This is an unaligned value; should we instead round it down to the
request_alignment granularity?
See below...
+++ b/include/block/block_int.h
@@ -695,6 +695,13 @@ typedef struct BlockLimits {
* clamped down. */
uint32_t max_transfer;
+/* Maximal hardware transfer length in bytes. Applies whenever
Leading /* on its own line, per our style.
The whole file still uses this style, I can change it if desired or do
it later for the whole file or even the whole block subsystem.
+ * 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.
+ */
Should we mandate any additional requirements on this value such as
multiple of request_alignment or even power-of-2?
Certainly not power of 2. Multiple of request_alignment probably makes
sense, but max_transfer doesn't have that limit.
Paolo
+uint64_t max_hw_transfer;
+
/* memory alignment, in bytes so that no bounce buffer is needed */
size_t min_mem_alignment;
Re: [PATCH v3 3/7] block: add max_hw_transfer to BlockLimits
On Thu, Jun 03, 2021 at 03:37:18PM +0200, Paolo Bonzini wrote:
> 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.
>
> +/* 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;
This is an unaligned value; should we instead round it down to the
request_alignment granularity?
> +
> +if (bs) {
> +max = MIN_NON_ZERO(bs->bl.max_hw_transfer, bs->bl.max_transfer);
> +}
> +return max;
> +}
> +
> /* Returns the maximum transfer length, in bytes; guaranteed nonzero */
> uint32_t blk_get_max_transfer(BlockBackend *blk)
> {
> +++ b/include/block/block_int.h
> @@ -695,6 +695,13 @@ typedef struct BlockLimits {
> * clamped down. */
> uint32_t max_transfer;
>
> +/* Maximal hardware transfer length in bytes. Applies whenever
Leading /* on its own line, per our style.
> + * 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.
> + */
Should we mandate any additional requirements on this value such as
multiple of request_alignment or even power-of-2?
> +uint64_t max_hw_transfer;
> +
> /* memory alignment, in bytes so that no bounce buffer is needed */
> size_t min_mem_alignment;
>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
[PATCH v3 3/7] block: add max_hw_transfer to BlockLimits
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
---
block/block-backend.c | 12
block/file-posix.c | 2 +-
block/io.c | 1 +
hw/scsi/scsi-generic.c | 2 +-
include/block/block_int.h | 7 +++
include/sysemu/block-backend.h | 1 +
6 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/block/block-backend.c b/block/block-backend.c
index 15f1ea4288..2ea1412a54 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1953,6 +1953,18 @@ 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(bs->bl.max_hw_transfer, bs->bl.max_transfer);
+}
+return max;
+}
+
/* 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 e3241a0dd3..f55f92d0f5 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1234,7 +1234,7 @@ 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 323854d063..089b99bb0c 100644
--- a/block/io.c
+++ b/block/io.c
@@ -127,6 +127,7 @@ 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 82e1e2ee79..3762dce749 100644
--- a/hw/scsi/scsi-generic.c
+++ b/hw/scsi/scsi-generic.c
@@ -179,7 +179,7 @@ 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 057d88b1fc..f1a54db0f8 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -695,6 +695,13 @@ 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 5423e3d9c6..9ac5f7bbd3 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -208,6 +208,7 @@ 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);
--
2.31.1
