From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53574) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cWQhY-00059a-Md for qemu-devel@nongnu.org; Wed, 25 Jan 2017 11:45:41 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cWQhV-0003s5-FG for qemu-devel@nongnu.org; Wed, 25 Jan 2017 11:45:40 -0500 From: Markus Armbruster References: <1485164923-17736-1-git-send-email-armbru@redhat.com> <1485164923-17736-7-git-send-email-armbru@redhat.com> <2fd376cd-e88a-b6da-d648-b80d35e74c7a@redhat.com> <877f5l1tak.fsf@dusky.pond.sub.org> <3512807d-d04e-50fa-9fcf-d1d5ba8ac350@redhat.com> <87r33saa6p.fsf@dusky.pond.sub.org> Date: Wed, 25 Jan 2017 17:45:27 +0100 In-Reply-To: <87r33saa6p.fsf@dusky.pond.sub.org> (Markus Armbruster's message of "Tue, 24 Jan 2017 13:56:14 +0100") Message-ID: <87vat33x7c.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH 6/6] hw/i386/i386: Stop auto-creating lsi53c895a SCSI HBAs List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson , Alexander Graf Cc: Paolo Bonzini , kwolf@redhat.com, Peter Maydell , qemu-devel@nongnu.org, qemu-block@nongnu.org, "Michael S . Tsirkin" David, Alex, got a sPAPR question for you. Markus Armbruster writes: > Cc'ing in sPAPR maintainers... [...] > Let me spell things out a bit more, to make sure we all agree on what > exactly we want to deprecate. > > After this series, -drive if=scsi works for the following machine types: > > * magnum pica61 LX SPARCClassic SPARCbook SS-10 SS-20 SS-4 SS-5 SS-600MP > Voyager > > The machine has an onboard SCSI HBA, which adopts the drives with > bus=0.. Drives with non-zero bus numbers stay orphaned. This is > exactly how other interface types work. > > Except when additional HBAs get cold-plugged somehow, non-zero bus > numbers can work; see below. > > * realview-eb realview-eb-mpcore versatileab versatilepb > > These create N lsi53c895a SCSI HBAs, where N is the largest value of > bus. If N is too large, machine initialization fails with a "no > slot/function available for lsi53c895a, all in use" error. > > This is just like the PC machine types work before this patch. > > * pseries-* > > Likewise, except create spapr-vscsi SCSI HBAs. Large N make machine > initialization s-l-o-w. I tried to find out whether and how it fails > when N is too large, but I lost patience. Totally unscientific experiment: run "qemu-system-ppc64 -S -display none -monitor stdio -M pseries,accel=qtest -drive if=scsi,media=cdrom,bus=N" for various N and check SZ in ps, with "ps -C qemu-system-ppc64 -O sz". Results: N SZ 0 339413 10 353182 20 375342 30 405857 40 444716 50 491988 60 547582 70 611589 80 683916 90 764658 100 853743 Definitely super-linear. Is this expected? No wonder my previous bus=999 experiement thrashed my machine; extrapolating from the above I guesstimate SZ in the order of 50 million pages. Of course, asking for 1000 spapr-vscsi devices is silly, but trashing is not a nice way to say "don't be silly". Should we reject bus=N when N exceeds a certain limit? Care to suggest a limit? [...]