Date: Mon, 17 Dec 2007 13:54:57 -0800 From: "Kip Macy" <kip.macy@gmail.com> To: "James Mansion" <james@mansionfamily.plus.com> Cc: freebsd-hackers@freebsd.org, Julian Elischer <julian@elischer.org> Subject: Re: kqueue and libev Message-ID: <b1fa29170712171354o35cec019i75a78ed54cddfa55@mail.gmail.com> In-Reply-To: <4766E92C.6020703@mansionfamily.plus.com> References: <4763A398.2040109@mansionfamily.plus.com> <47644BFE.3060003@elischer.org> <b1fa29170712151407v4eca6a78hda7dd75ab9367ca7@mail.gmail.com> <4766E92C.6020703@mansionfamily.plus.com>
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On Dec 17, 2007 1:25 PM, James Mansion <james@mansionfamily.plus.com> wrote: > Kip Macy wrote: > >> he's just plain misinforme > > Until we know what he is referring to we can't actually say that. > > -Kip > > > > OK he said I could post from our private email so here goes. There were > bits in and around relating to the > Solaris /dev/poll support (and the mechanism's limitations) which I've > elided. > > I think the most telling thing is probably that drivers need to provide > support and that a single mechanism > in the driver doesn't support select and poll at the same time - which I > guess lines up with the reported failure > with USB serial. > > Does kqueue work with USB for example? How about an AIO request to read > from a USB endpoint? > > It may well just be a case of 'fessing up to system limitations. > > James > > ============================================================================ > > Compile and install rxvt-unicode on freebsd and run it with: > > urxvt # works, uses select (or maybe poll) > LIBEV_FLAGS=8 urxvt # acts weird, uses kqueue > > (note: only works when urxvt isn't set[gu]id) > > The typical symptoms are either delayed notificatrions, no notifications at > all or _continuous_ notifications and read failing with EAGAIN. Here is a > ktrace showing the latter: http://ue.tst.eu/45eb8a3c3e812933cbe3172af2ee4a6c.txt > > kqueue works well with sockets (or with about anything on netbsd), but > fails on more exotic types such as ptys. (I test on Freebsd 6.2 RELEASE, > but got reports about problems with earlier and later versions, too, > as well as on openbsd (which I didn't verify) and on darwin (which is > completely broken)). > > > > You normally don't get useful writeable/readable state for files, > > > No, I only want the same readyness notifications as with select or poll, > as is documented in the manpage. (even on platforms where kqueue works > this requires some heuristics and workarounds with kqueue due to design > limitations (for example problems with close() or fork() that force > constant rearming), but thats common in interfaces like kqueue, and by now > well understood and handled by libev). > > > > Actually, until recently it was broken on pipes. We've never received > > any PRs to that effect so there is no way of knowing. You'll have > > better luck asking the author himself. To be more precise, this only manifested itself in erlang. > > Well, one should better document the types with which it works (which on > freebsd apparently includes sockets and nothing else). I also think one > should rethink the internal design if every driver needs its own kqueue > support, as that will always force kqueue into a second-class citizen not > suitable as replacement for select, as it's unreasonable to expect kqueue > to just work when its so little used and requires such a high maintainance > (linux' epoll for example works fine with everything because it doesn't > require drivers to support epoll specifically, so it is unlikely that > epoll fails when select would work for example, which is the case on > freebsd and darwin). > > The fact that it works fine on everything I threw at it on netbsd is > probably not the result of better design, but more better maintainance, so > I wouldn't be surprised if some future version of netbsd failed in similar > ways (OTOH, in the past, netbsd consistently was the less buggy platform > regardless of topic, wether it was threads, ptys or kqueue, so I might get > quite disappointed if that happened :) Interesting, that has been completely counter to my experience. However, I rely on a completely different set of subsystems. Do you have a set of regression tests for libev? It sounds like they would worth having to regression test kqueue. Thanks for your feedback. -Kip
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