Date: Fri, 11 Mar 2005 17:28:05 +0300 From: Gleb Smirnoff <glebius@FreeBSD.org> To: Pawel Jakub Dawidek <pjd@FreeBSD.org> Cc: ru@FreeBSD.org Subject: Re: Giant-free polling [PATCH] Message-ID: <20050311142805.GB88801@cell.sick.ru> In-Reply-To: <20050311141450.GF9291@darkness.comp.waw.pl> References: <20050311110234.GA87255@cell.sick.ru> <E1D9kbt-000FAj-00._pppp-mail-ru@f22.mail.ru> <20050311141450.GF9291@darkness.comp.waw.pl>
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On Fri, Mar 11, 2005 at 03:14:50PM +0100, Pawel Jakub Dawidek wrote: P> On Fri, Mar 11, 2005 at 04:55:25PM +0300, dima wrote: P> +> I thought about using list also, but considered it to bring P> +> too much overhead to the code. The original idea of handling arrays P> +> seems to be very elegant. P> P> Overhead? Did you run any benchmarks to prove it? P> I find list-version much more elegant that using an array. It is also a small cookie for future. Now we have IFF_POLLING flag and IFCAP_POLLING, which indicate whether interface support polling and whether it actually does polling. This is not nice, from my viewpoint. I'd like to see only IFCAP_POLLING present and turning polling on/off for particular interface should be done by inserting/removing iface from polling list. This will also remove an extra unlocked check of interface flags (?). P> I also don't like the idea of calling handler method with two locks P> held (one sx and one mutex)... I agree with Pawel. We have LOR here between sx lock and driver lock: normal polling: (get sx shared) -> (get driver mutex) driver stop: (get driver mutex) -> (get sx exclusive) We will have deadlock if this two things process in parallel. And the per-interface mutex protects only reentrancy of interface poll method, is that right? P> There is still an unresolved problem (in your and our patch as well) of P> using ifnet structure fields without synchronization, as we don't have P> access tointerface's internal mutex, which protects those fields. This is unresolved in our patch, too, and I believe throughout many other places in kernel. -- Totus tuus, Glebius. GLEBIUS-RIPN GLEB-RIPE
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