Re: [PATCH] block: introduce max_hw_iov for use in scsi-generic

[Michael Roth via <qemu-devel@nongnu.org>]

On Fri, Sep 24, 2021 at 08:50:05AM +0200, Christian Borntraeger wrote:
> Peter, Michael,
> 
> do we still do stable releases for QEMU or has this stopped?

Hi Christian,

Yes, it's just been a perfect storm of job moves / bad timing / much-needed
testing rework. I plan to restart the stable releases starting with 6.0.1 and
6.1.1 shortly after. I'll get the release schedules posted on the release wiki
week.

Sorry for the delays on this.

-Mike

> 
> Am 24.09.21 um 07:27 schrieb Paolo Bonzini:
> > 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 ZjQcmQRYFpfptBannerStart
> > This Message Is From an External Sender
> > This message came from outside your organization.
> > ZjQcmQRYFpfptBannerEnd
> > 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);
> >      >
> >