Date: Wed, 25 Feb 2015 17:18:10 -0700 From: Warner Losh <imp@bsdimp.com> To: John Baldwin <jhb@FreeBSD.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-arch@freebsd.org Subject: Re: locks and kernel randomness... Message-ID: <871FF097-7372-4901-8202-003398B6ABE3@bsdimp.com> In-Reply-To: <1774232.7ZAkabLA24@ralph.baldwin.cx> References: <DD06E2EA-68D6-43D7-AA17-FB230750E55A@bsdimp.com> <54ED87E9.8030706@astrodoggroup.com> <20150225085659.GA74514@kib.kiev.ua> <1774232.7ZAkabLA24@ralph.baldwin.cx>
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[-- Attachment #1 --] > On Feb 25, 2015, at 1:20 PM, John Baldwin <jhb@FreeBSD.org> wrote: > > On Wednesday, February 25, 2015 10:56:59 AM Konstantin Belousov wrote: >> The cost of the proposed patch, of course, is not the several >> thousands of instructions in the rebalance. The problem with it is the >> introduction of the new spinlock, which will be used in many places >> after the introduction. The cost of the new and often used spinlock is >> the increase of both interrupt latency and interrupt handler jitter and >> cpu switch jitter. >> >> So neither buildworld timing, nor network throughput are adequate >> to estimate the change. It is system unresponsivness and loss of >> the realtime behaviour up to some degree. >> >> I thought that it was obvious, at least after spinlocks were mentioned, >> but apparently it is not, since proposals to measure the patch effect >> by benchmarking buildworld or passing the traffic are made. > > +1 > > The only thing I will add is that in general this makes the system more > fragile and complex as well. Please just stay with a regular mutex and change > the scheduler to not use random() (which seems to be in progress?). I'm not > sure why we needed the extra 40 messages in this thread after that was > effectively said the first time. If you’d like to be helpful, please review https://reviews.freebsd.org/D1968 Harrison Grundy wrote it, and I put it in phabricator for him while he sorts out his own account. In a fit of passive aggressiveness, I’ve added everybody who commented on this thread as reviewers, except Bruce and Harrison who don’t have accounts yet. Warner [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJU7mZCAAoJEGwc0Sh9sBEA3VsP/iNIgP9IbRVC8ZYh2yUx/9fX PRLC4Iqsj2ZakIdPaP3YnRXHEmrwEN8l2G6Zcf/rtJu1EZojyhdzAwW8cgdh6kfj 2AWmR2IjEph3FLiFFo2endZTwFvdE2SBj34uda45xV2ow4q98UvdliOKE9+ba0z1 7eaOSXjqYY3J1mCETHxfEDc08lf1qiRwxVtN2QwaCmzH0/l7a9QgLFvgbbD4sxyh /zf8xvnUG9CAj7HxCFrBs3r9NkFE9ifx6SBZxxK2mycv/YZKHF4ESp3XUXngy31Y hsJjC/m2SQQlCmoV4tACZQ4wL7TqI9wobBejr0wUGV6pbdGGhhrdhxDsfQHnJb8v W4gRQCBAIbNvYztyPql0LZuSC2ZQftCSOW/KHel0eZnvbIS/+wUAbzgrQgt4U0Ps tf2nX73vVCOh7SiW09ybezpK71F9NDFiKfQmYYYzquYJ6v8gHigjBnSaZlrnh2IC iY2s69wB+Huge6v/VMg4HsoDD6tXpAtf9Z/D9Lv4Ona17aLW9EQi2F0CPXTskxfX BJauYUzGPMyMWxqU3rbCXGAAzSF4ybxC6QE+e9n2ag6JpErqH3BLX9Ck6jfUQplk 19AU1DPFvde9Qt5Agj+Qnnde8jMhOmfv071GjQLDNWnrWncQFG8xzwXzLCe6cUME OQ96bfjh5fjZi/Uwi744 =EXES -----END PGP SIGNATURE-----
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