Re: [Qemu-devel] Modularizing QEMU RFC

[Fam Zheng]

On Mon, 08/03 12:22, Marc Marí wrote:
> On Mon, 3 Aug 2015 17:24:57 +0800
> Fam Zheng <address@hidden> wrote:
> 
> > On Mon, 08/03 11:01, Marc Marí wrote:
> > > Some profiling:
> > > 
> > > A QEMU with this configuration:
> > > ./configure --enable-sparse --enable-sdl --enable-gtk --enable-vte \
> > >  --enable-curses --enable-vnc --enable-vnc-{jpeg,tls,sasl,png,ws} \
> > >  --enable-virtfs --enable-brlapi --enable-curl --enable-fdt \
> > >  --enable-bluez --enable-kvm --enable-rdma --enable-uuid
> > > --enable-vde \ --enable-linux-aio --enable-cap-ng --enable-attr
> > > --enable-vhost-net \ --enable-vhost-scsi --enable-spice
> > > --enable-rbd --enable-libiscsi \ --enable-smartcard-nss
> > > --enable-guest-agent --enable-libusb \ --enable-usb-redir
> > > --enable-lzo --enable-snappy --enable-bzip2 \ --enable-seccomp
> > > --enable-coroutine-pool --enable-glusterfs \ --enable-tpm
> > > --enable-libssh2 --enable-vhdx --enable-quorum \ --enable-numa
> > > --enable-tcmalloc --target-list=x86_64-softmmu
> > > 
> > > Has dependencies on 142 libraries. It takes 60 ms between the run
> > > and the jump to the main function, and 80 ms between the run and the
> > > first kvm_entry.
> > > 
> > > A QEMU with the same configuration and --enable-modules has
> > > dependencies on 125 libraries. It takes 20 ms between the run and
> > > the jump to the main function, and 100 ms between the run and the
> > > first kvm_entry.
> > 
> > Which means 40 ms is saved because we reduced the size and dependency
> > of QEMU executable, but 60 ms is the extra cost of dynamical loading.
> > That's a net loss.
> > 
> > In your --enable-modules configuration, could you try comment out
> > module_load body and compare again, so we know how much time is spent
> > in looking up and loading modules?
> > 
> 
> With the module load disabled, 20 ms from run to main, and 40 ms from
> run to kvm_entry. Which is "the expected", from the numbers above.
> 

Thanks, that proves the 40 ms speeding up is already waving hands. :)

Once you figure out a way to map protocol/format names to module names in
block.c, we can review all "QLIST_FOREACH(drv, &bdrv_drivers, list)" there, to
either inject loading of all modules, or change it to loading of a specific
module.

Fam