virtio-blk: use larger default request size

[SeaBIOS] [PATCH] virtio-blk: use larger default request size

Posted by Gerd Hoffmann 8 months, 3 weeks ago

Bump default from 8 to 64 blocks.  Using 8 by default leads
to requests being splitted on qemu, which slows down boot.

Some (temporary) debug logging added showed that almost all
requests on a standard fedora install are less than 64 blocks,
so that should bring us back to 1.15 performance levels.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 src/hw/virtio-blk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/hw/virtio-blk.c b/src/hw/virtio-blk.c
index 929ba8873dc0..9b4a05a4c424 100644
--- a/src/hw/virtio-blk.c
+++ b/src/hw/virtio-blk.c
@@ -95,7 +95,7 @@ virtio_blk_op(struct disk_op_s *op, int write)
         blk_num_max = (u16)max_io_size / vdrive->drive.blksize;
     else
         /* default blk_num_max if hardware doesnot advise a proper value */
-        blk_num_max = 8;
+        blk_num_max = 64;
 
     if (op->count <= blk_num_max) {
         virtio_blk_op_one_segment(vdrive, write, sg);
-- 
2.36.1

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[SeaBIOS] Re: [PATCH] virtio-blk: use larger default request size

Posted by Kevin O'Connor 8 months, 3 weeks ago

On Thu, Jul 07, 2022 at 12:06:16PM +0200, Gerd Hoffmann wrote:
> Bump default from 8 to 64 blocks.  Using 8 by default leads
> to requests being splitted on qemu, which slows down boot.
> 
> Some (temporary) debug logging added showed that almost all
> requests on a standard fedora install are less than 64 blocks,
> so that should bring us back to 1.15 performance levels.

Thanks.  Looks fine to me.

-Kevin
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[SeaBIOS] Re: [PATCH] virtio-blk: use larger default request size

Posted by Gerd Hoffmann 8 months, 1 week ago

On Thu, Jul 07, 2022 at 11:13:52AM -0400, Kevin O'Connor wrote:
> On Thu, Jul 07, 2022 at 12:06:16PM +0200, Gerd Hoffmann wrote:
> > Bump default from 8 to 64 blocks.  Using 8 by default leads
> > to requests being splitted on qemu, which slows down boot.
> > 
> > Some (temporary) debug logging added showed that almost all
> > requests on a standard fedora install are less than 64 blocks,
> > so that should bring us back to 1.15 performance levels.
> 
> Thanks.  Looks fine to me.

Pushed now.

take care,
  Gerd

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