From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36621) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZOTS4-0007rJ-Fc for qemu-devel@nongnu.org; Sun, 09 Aug 2015 12:28:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZOTRz-00050Q-G4 for qemu-devel@nongnu.org; Sun, 09 Aug 2015 12:28:00 -0400 Received: from mail-wi0-f169.google.com ([209.85.212.169]:37647) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZOTRz-00050I-9o for qemu-devel@nongnu.org; Sun, 09 Aug 2015 12:27:55 -0400 Received: by wibhh20 with SMTP id hh20so121561652wib.0 for ; Sun, 09 Aug 2015 09:27:54 -0700 (PDT) References: <1438966995-5913-1-git-send-email-a.rigo@virtualopensystems.com> <1438966995-5913-6-git-send-email-a.rigo@virtualopensystems.com> <20150808124401.GA18166@aurel32.net> <871tfcnann.fsf@linaro.org> <20150809084020.GA5883@aurel32.net> <87zj20lrhc.fsf@linaro.org> <20150809101310.GB5883@aurel32.net> From: Alex =?utf-8?Q?Benn=C3=A9e?= In-reply-to: <20150809101310.GB5883@aurel32.net> Date: Sun, 09 Aug 2015 17:27:52 +0100 Message-ID: <87y4hkl94n.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [RFC v4 5/9] configure: Enable/disable new qemu_{ld, st} excl insns List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Aurelien Jarno Cc: mttcg@listserver.greensocs.com, claudio.fontana@huawei.com, Alvise Rigo , qemu-devel@nongnu.org, pbonzini@redhat.com, jani.kokkonen@huawei.com, tech@virtualopensystems.com Aurelien Jarno writes: > On 2015-08-09 10:51, Alex Bennée wrote: >> >> Aurelien Jarno writes: >> >> > On 2015-08-09 09:11, Alex Bennée wrote: >> >> >> >> Aurelien Jarno writes: >> >> >> >> > On 2015-08-07 19:03, Alvise Rigo wrote: >> >> >> Introduce the new --enable-tcg-ldst-excl configure option to enable the >> >> >> LL/SC operations only for those backends that support them. >> >> >> >> >> >> Suggested-by: Jani Kokkonen >> >> >> Suggested-by: Claudio Fontana >> >> >> Signed-off-by: Alvise Rigo >> >> >> --- >> >> >> configure | 21 +++++++++++++++++++++ >> >> >> 1 file changed, 21 insertions(+) >> >> > >> >> > We have seen that for this kind of patch, it's better to add support in >> >> > all backends, otherwise it takes ages to get all the backends converted. >> >> > I think you should involve the backend maintainers. I can try to provide >> >> > the corresponding patches for mips and ia64. >> >> >> >> We discussed this on the last MTTCG call and agree. However we will need >> >> help from the other TCG maintainers for the backends. The changes should >> >> be fairly mechanical though. >> >> >> >> However in the spirit of keeping trees building in the meantime should >> >> we change this from a configure option to just a static option for each >> >> given backend as it is converted? >> > >> > I am not even sure we need a static option. I guess providing we are >> > doing that early enough in the 2.5 cycle, we can just add the new ops >> > and start using them. Of course we should put the backends maintainers >> > in the loop so they can fix that quickly and don't get a surprise weeks >> > afters. >> > >> > That said, please see my other email, I am not sure we actually need to >> > modify backends, I think we can implement these new "ops" through >> > tcg-runtime. >> >> We still need to ensure "normal" ld/st operations trip the exclusive bit >> though. > > Isn't that taken care of by the TLB_EXCL flag, causing pages in > exclusive mode to always go through the slow path? Then we should not > need to modify the backends as they already check for non zero bits in > this area. Ahh I see. Yes of course that sounds like a good idea. -- Alex Bennée