Re: [PATCH 0/5] ArmVirtPkg, OvmfPkg: improve firmware duration of direct kernel boot

[Laszlo Ersek <lersek@redhat.com>]

On 03/16/18 10:59, Richard W.M. Jones wrote:
> On Thu, Mar 15, 2018 at 08:02:53PM +0100, Laszlo Ersek wrote:
>> Please attach a good number of disks at once on the command line,
> 
> I read this bit then forgot to do it :-/
> 
> The test suite has a test for adding a large number of drives:
> 
>   https://github.com/libguestfs/libguestfs/tree/master/tests/disks
> 
> so it's quite easy for me to test this:
> 
>   $ time ./test-add-disks -n 100

What kind of disks does this test add, virtio-blk or virtio-scsi?

And I assume PCI, not virtio-mmio?

It's possible that with a hundred disks, you hit a limit in the firmware
before all the time was spent that would have been necessary to bind all
hundred disks. I mean, the point is exactly to prevent the firmware from
spending time on those disks, but it should be due to a controlled
restriction, not resource exhaustion, and the comparison should use a
test case where the firmware does manage to bind them all (without the
patches).

... We could go into the various limits here, regarding PCI bus number
space, virtio-scsi targets and LUNs, but I think it would be premature
before seeing a domain XML or a QEMU command line. (Also, my apologies
for being vague with "good number of ...".)

Furthermore:

> Results with Fedora's edk2-aarch64:
> 
>   real	8m25.353s
>   user	0m2.393s
>   sys	0m2.657s
> 
> Results with your file:
> 
>   real	8m15.285s
>   user	0m0.178s
>   sys	0m0.381s
> 
> So there's not really a great difference here, but boot time is not a
> significant factor for this test unlike the boot benchmark tests.

indeed this patch should only improve boot time. In your other email,
you mention "libguestfs-boot-benchmark". Does that include kernel boot
time as well?

... OTOH, it probably should too. An interactive user definitely cares
about the time between (a) hitting Enter on the "guestfish" command and
(b) getting the guestfish prompt. Where the boot transitions from
firmware to kernel is irrelevant to the user.

Sorry to bother you with another request, but I currently have no access
to my aarch64 hardware (so that I could test on aarch64 KVM); could you
please compare boot benchmark results using, say, eight disks? Something
like:

  time guestfish --ro \
    -a disk1.img \
    ... \
    -a disk8.img \
    launch : quit

(I hope this test case is not totally bogus.)

If you don't have time, I'll try to run this test myself tonight. I'd
trust your results more though!

Thanks!
Laszlo