From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47636) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZMCAX-0004Hf-B1 for qemu-devel@nongnu.org; Mon, 03 Aug 2015 05:36:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZMCAS-00047G-AD for qemu-devel@nongnu.org; Mon, 03 Aug 2015 05:36:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40503) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZMCAS-00046S-1h for qemu-devel@nongnu.org; Mon, 03 Aug 2015 05:36:24 -0400 Date: Mon, 3 Aug 2015 11:36:18 +0200 From: Marc =?UTF-8?B?TWFyw60=?= Message-ID: <20150803113618.454a723f@markmb_rh> In-Reply-To: <87r3nklo5z.fsf@linaro.org> References: <20150731174542.44862e3a@markmb_rh> <20150803030906.GA13938@ad.nay.redhat.com> <20150803095238.663a7bee@markmb_rh> <20150803082234.GA30561@ad.nay.redhat.com> <20150803110147.55ede584@markmb_rh> <87r3nklo5z.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] Modularizing QEMU RFC List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alex =?UTF-8?B?QmVubsOpZQ==?= Cc: Fam Zheng , qemu-devel On Mon, 03 Aug 2015 10:24:56 +0100 Alex Benn=C3=A9e wrote: >=20 > Marc Mar=C3=AD writes: >=20 > > On Mon, 3 Aug 2015 16:22:34 +0800 > > Fam Zheng wrote: > > > >> On Mon, 08/03 09:52, Marc Mar=C3=AD wrote: > >> > So any other ideas to reduce the library overhead are > >> > appreciated. > >>=20 > >> It would be interesting to see your profiling on the library > >> loading overhead. For example, how much does it help to reduce the > >> library size, and how much does it help to reduce the # of > >> libraries? > > > > > 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=3Dx86_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. > > > > The libraries that are not loaded are: libiscsi, libcurl, librbd, > > librados, ligfapi, libglusterfs, libgfrpc, libgfxdr, libssh2, > > libcrypt, libidin, libgssapi, liblber, libldap, libboost_thread, > > libbost_system and libatomic_ops. > > > > As I already explained, the current implementation of modules loads > > the modules at startup always. That's why the QEMU setup takes > > longer, even though it uses G_MODULE_BIND_LAZY. And that's why I > > was proposing hotplugging. > > > > I don't know if loading one big library is more efficent than a lot > > of small ones, but it would make sense. >=20 > What's the actual use-case here where start-up latency is so > important? If it is an ephemeral cloudy thing then you might just > have a base QEMU with VIRT drivers and one big .so call "the-rest.so"? >=20 > I don't wish to disparage the idea but certainly in emulation world > the difference of 100ms or so is neither here nor there. >=20 Clear Containers: https://lwn.net/Articles/644675/ We are looking for making QEMU more lightweight for the general use case and also for the container use case. It is a lot better to have the same tool for both cases, and not start a new one from scratch as Intel has done. This also benefits the general QEMU community, and that's why I'm having this discussion here. If there's a point where QEMU is still too slow for containers, but optimizing means breaking, then we will have to take a step back and change the point of view. And making QEMU modular I think is benefitial for everyone. Marc