Yes, the question is whether it still exists... Paolo El jue., 23 sept. 2021 16:48,
Christian Borntraeger <borntraeger@de.ibm.com> escribió: Am 23.09.21 um 15:04
schrieb Paolo Bonzini: > Linux limits the size of iovecs to 1024 (UIO_MAXIOV
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Yes, the question is whether it still exists...
Paolo
El jue., 23 sept. 2021 16:48, Christian Borntraeger <borntraeger@de.ibm.com
<mailto:borntraeger@de.ibm.com>> escribió:
Am 23.09.21 um 15:04 schrieb Paolo Bonzini:
> Linux limits the size of iovecs to 1024 (UIO_MAXIOV in the kernel
> sources, IOV_MAX in POSIX). Because of this, on some host adapters
> requests with many iovecs are rejected with -EINVAL by the
> io_submit() or readv()/writev() system calls.
>
> In fact, the same limit applies to SG_IO as well. To fix both the
> EINVAL and the possible performance issues from using fewer iovecs
> than allowed by Linux (some HBAs have max_segments as low as 128),
> introduce a separate entry in BlockLimits to hold the max_segments
> value from sysfs. This new limit is used only for SG_IO and clamped
> to bs->bl.max_iov anyway, just like max_hw_transfer is clamped to
> bs->bl.max_transfer.
>
> Reported-by: Halil Pasic <pasic@linux.ibm.com
<mailto:pasic@linux.ibm.com>>
> Cc: Hanna Reitz <hreitz@redhat.com <mailto:hreitz@redhat.com>>
> Cc: Kevin Wolf <kwolf@redhat.com <mailto:kwolf@redhat.com>>
> Cc: qemu-block@nongnu.org <mailto:qemu-block@nongnu.org>
> Fixes: 18473467d5 ("file-posix: try BLKSECTGET on block devices too, do not
round to power of 2", 2021-06-25)
This sneaked in shortly before the 6.1 release (between rc0 and rc1 I
think).
Shouldnt that go to stable in cass this still exist?
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com
<mailto:pbonzini@redhat.com>>
> ---
> block/block-backend.c | 6 ++++++
> 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, 17 insertions(+), 2 deletions(-)
>
> diff --git a/block/block-backend.c b/block/block-backend.c
> index 6140d133e2..ba2b5ebb10 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -1986,6 +1986,12 @@ uint32_t blk_get_max_transfer(BlockBackend *blk)
> return ROUND_DOWN(max, blk_get_request_alignment(blk));
> }
>
> +int blk_get_max_hw_iov(BlockBackend *blk)
> +{
> + return MIN_NON_ZERO(blk->root->bs->bl.max_hw_iov,
> + blk->root->bs->bl.max_iov);
> +}
> +
> int blk_get_max_iov(BlockBackend *blk)
> {
> return blk->root->bs->bl.max_iov;
> diff --git a/block/file-posix.c b/block/file-posix.c
> index cb9bffe047..1567edb3d5 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1273,7 +1273,7 @@ static void raw_refresh_limits(BlockDriverState
*bs, Error **errp)
>
> ret = hdev_get_max_segments(s->fd, &st);
> if (ret > 0) {
> - bs->bl.max_iov = ret;
> + bs->bl.max_hw_iov = ret;
> }
> }
> }
> diff --git a/block/io.c b/block/io.c
> index a19942718b..f38e7f81d8 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -136,6 +136,7 @@ static void bdrv_merge_limits(BlockLimits *dst,
const BlockLimits *src)
> dst->min_mem_alignment = MAX(dst->min_mem_alignment,
> src->min_mem_alignment);
> dst->max_iov = MIN_NON_ZERO(dst->max_iov, src->max_iov);
> + dst->max_hw_iov = MIN_NON_ZERO(dst->max_hw_iov, src->max_hw_iov);
> }
>
> typedef struct BdrvRefreshLimitsState {
> diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
> index 665baf900e..0306ccc7b1 100644
> --- a/hw/scsi/scsi-generic.c
> +++ b/hw/scsi/scsi-generic.c
> @@ -180,7 +180,7 @@ static int scsi_handle_inquiry_reply(SCSIGenericReq
*r, SCSIDevice *s, int len)
> page = r->req.cmd.buf[2];
> if (page == 0xb0) {
> uint64_t max_transfer =
blk_get_max_hw_transfer(s->conf.blk);
> - uint32_t max_iov = blk_get_max_iov(s->conf.blk);
> + uint32_t max_iov = blk_get_max_hw_iov(s->conf.blk);
>
> assert(max_transfer);
> max_transfer = MIN_NON_ZERO(max_transfer, max_iov *
qemu_real_host_page_size)
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index f1a54db0f8..c31cbd034a 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -702,6 +702,13 @@ typedef struct BlockLimits {
> */
> uint64_t max_hw_transfer;
>
> + /* Maximal number of scatter/gather elements allowed by the
hardware.
> + * Applies whenever transfers to the device bypass the kernel I/O
> + * scheduler, for example with SG_IO. If larger than max_iov
> + * or if zero, blk_get_max_hw_iov will fall back to max_iov.
> + */
> + int max_hw_iov;
> +
> /* 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 29d4fdbf63..82bae55161 100644
> --- a/include/sysemu/block-backend.h
> +++ b/include/sysemu/block-backend.h
> @@ -211,6 +211,7 @@ 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);
> +int blk_get_max_hw_iov(BlockBackend *blk);
> void blk_set_guest_block_size(BlockBackend *blk, int align);
> void *blk_try_blockalign(BlockBackend *blk, size_t size);
> void *blk_blockalign(BlockBackend *blk, size_t size);
>