Date: Sat, 27 Oct 2012 17:27:36 +0100 From: Attilio Rao <attilio@freebsd.org> To: Andre Oppermann <andre@freebsd.org> Cc: mdf@freebsd.org, src-committers@freebsd.org, John Baldwin <jhb@freebsd.org>, svn-src-user@freebsd.org, Jeff Roberson <jroberson@jroberson.net>, Bruce Evans <brde@optusnet.com.au> Subject: Re: svn commit: r241889 - in user/andre/tcp_workqueue/sys: arm/arm cddl/compat/opensolaris/kern cddl/contrib/opensolaris/uts/common/dtrace cddl/contrib/opensolaris/uts/common/fs/zfs ddb dev/acpica dev/... Message-ID: <CAJ-FndAhYk4R2AD3COmkOv3vYQganGXQKuO%2BkMQLaefTQSAejQ@mail.gmail.com> In-Reply-To: <CAJ-FndC%2BujncG54_RMwKwdtvNCRJ2QojNuADWn59puwayCHs6A@mail.gmail.com> References: <201210221418.q9MEINkr026751@svn.freebsd.org> <201210241136.06154.jhb@freebsd.org> <CAJ-FndAG-Qp%2B1aQvoL7YRj=R151Qe9_wNrUeOAaDsdYao_-zCQ@mail.gmail.com> <201210241414.30723.jhb@freebsd.org> <CAJ-FndAu6BGeMMbtFTLaSqy82mbhM9CVEyJ3Lb1WhAogJr59yA@mail.gmail.com> <CAJ-FndBqRpkBhCntd2aqwVYPu%2B2EHGeuXr5srLtrNNDK-ButxA@mail.gmail.com> <508965B3.2020705@freebsd.org> <CAJ-FndCMMH2Qy=rzzxagNVfgO9vF0xZY6B_vrnjmv_dXKNB5Dg@mail.gmail.com> <5089A913.2040603@freebsd.org> <CAJ-FndApwOo8xmZQyeqq0bGp8P13QWRqgmSDNg1_hbm7nrpOAQ@mail.gmail.com> <508A89EF.5070805@freebsd.org> <CAJ-FndC%2BujncG54_RMwKwdtvNCRJ2QojNuADWn59puwayCHs6A@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Sat, Oct 27, 2012 at 3:35 PM, Attilio Rao <attilio@freebsd.org> wrote: > On 10/26/12, Andre Oppermann <andre@freebsd.org> wrote: >> On 26.10.2012 08:27, Attilio Rao wrote: >>> On Thu, Oct 25, 2012 at 10:03 PM, Andre Oppermann <andre@freebsd.org> >>> wrote: >>>> On 25.10.2012 18:21, Attilio Rao wrote: >>>>> Did you see my (and also Jeff) objection to your proposal about this? >>>>> You are deliberating ignoring this? >>>> >>>> >>>> Well, I'm allowed to have a different opinion, am I? I'm not ignoring >>>> your objection in the sense as I'm not trying to commit any of this to >>>> HEAD while it is disputed. >>>> >>>> Mind you this whole conversation was started because I was trying to >>>> solve >>>> a problem with unfortunate cache line sharing for global mutexes in the >>>> kernel .bss section on my *personal* svn branch. >>> >>> Andre, >>> I'm sorry if you felt I was being harsh or confrontative. This was >>> really not my intention and I apologize. >> >> I apologize too for being a bit difficult and taking some time understand >> the differences in __aligned() regarding padding behavior. >> >>> Said that, I fail in seeing a proper technical discussion on your side >>> on how what I propose is "overdoing it" or how do you plan to address >>> the concerns people are raising with your proposal of bumping all lock >>> sizes indiscriminately. >> >> I'm wary of micro-optimizing and generally prefer clean and for a >> reader obvious approaches. That said my assumption on the distribution >> of mutex use cases in the kernel was wrong. By counting from a grep >> it seems that about half of the mutexes could possibly benefit from >> being padded and the other half doesn't because it is in structures >> and next to its data. > > Besides that, you are likely misunderstanding something about what I > propose: what I'm proposing is completely transparent to developers. > You will just need to declare a mtx like: > > struct mtx_unshare Giant; > > and then you can use the mtx(9) interface on it without any issue. I > don't see how this is less clean than what you propose. It just > enables the alignment/padding on a selection basis rather than > indiscriminately. > >>> However, here is the first half of the patch I'd like to see in: >>> http:///www.freebsd.org/~attilio/mtx_decoupled.patch >> > >>> This is just the part to give the ability to crunch different >>> structures to the mtx KPI. Please note that from the users perspective >>> the mtx KPI remains absolutely the same, so there is theoretically no >>> KPI discontinuity, the support is absolutely transparent. >> >> This seems rather complicated. Instead of mtxlock2mtx() wouldn't >> __containerof() work just as well? The __DEVOLATILE() looks a bit >> dangerous. Are you sure the compiler won't reorder things it should >> not? > > What do you mean with "rather complicated"? > For the users of the primitive nothing changes at all. > For the people that might read the code it is pretty much > self-explanatory, in particular if you know how lock classes work in > our locking scheme. Maybe I can add a comment or two to clarify. Here we go with further comments tweaks. Also, in order to make it a complete NOP from KPI perspective I had to change the way the mtx_assert() wrapper was implemented as in v1 it wasn't correctly handling the const qualifier. I think the result is better now and you should refer to this patch for reviews: http://www.freebsd.org/~attilio/mtx_decoupled2.patch Thanks, Attilio -- Peace can only be achieved by understanding - A. Einstein
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAJ-FndAhYk4R2AD3COmkOv3vYQganGXQKuO%2BkMQLaefTQSAejQ>