Date: Sun, 2 Nov 2014 22:17:26 +0100 From: Attilio Rao <attilio@freebsd.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org> Subject: Re: svn commit: r273966 - in head: share/man/man9 sys/kern sys/sys Message-ID: <CAJ-FndBz25uka6Zz%2Bx_bRykJCUQLCPxJoPHidc5FuTtZ=Kfb9w@mail.gmail.com> In-Reply-To: <20141102191029.GA53947@kib.kiev.ua> References: <201411021310.sA2DAWmD003298@svn.freebsd.org> <CAJ-FndB5%2BhhHprTiV1ODJoE9RNZLtOe2eQDi3MEpgPKYbM3LAw@mail.gmail.com> <20141102163728.GX53947@kib.kiev.ua> <CAJ-FndAeh_i9F98Tq-ZXgX%2Badq4mOgoadSoYJ6hmvYpBtmkvow@mail.gmail.com> <20141102165916.GY53947@kib.kiev.ua> <CAJ-FndAbhBFQ1gD64Wi210zH-0kfxjkkUJRNYHnFnmW%2BKAhm2w@mail.gmail.com> <20141102174958.GZ53947@kib.kiev.ua> <CAJ-FndC_3Te6Y7N0%2B8ZddH8i72cxH%2BACHm=EShHp=QDoX4xSow@mail.gmail.com> <20141102191029.GA53947@kib.kiev.ua>
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On Sun, Nov 2, 2014 at 8:10 PM, Konstantin Belousov <kostikbel@gmail.com> wrote: > On Sun, Nov 02, 2014 at 06:53:44PM +0100, Attilio Rao wrote: >> > I did not proposed to verify owner chain. I said that it is easy to >> > record the locks owned by current thread, only for current thread >> > consumption. Below is the prototype. >> >> I think it is too expensive, think that this must happen for every shared lock. >> I know we may not be using too many shared locks on lockmgr right now, >> but it is not a good reason to make shared lock bloated and more >> expensive on lockmgr. > > It can be significantly simplified, if the array of lock pointers is > kept dense. Then the only non-trivial operation is unlock out of order, > when the array have to be compacted. > > The code adds one write and n reads on shared lock, where n is the > number of shared-locked locks already owned by thread. Typical n is 0 > or 1. On unlock, if done in order, the code adds one read; unordered > unlock shuffles array elements. Again, for typical lock nesting of 2, > this means one read and one write, and even this is rare. All reads and > writes are for thread-local memory. > > I am not going to spend any more time on this if people do not consider > the lock tracking worth it. Otherwise, I will benchmark the patch. I think that your initial patch (what is in head now) is a better approach. I would just make it a lockinit() flag to make it less alien to the KPI. Attilio -- Peace can only be achieved by understanding - A. Einstein
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