Date: Tue, 3 Mar 2015 09:27:45 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Julian Elischer <julian@freebsd.org> Cc: Davide Italiano <davide@freebsd.org>, "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>, Neel Natu <neelnatu@gmail.com> Subject: Re: svn commit: r279539 - head/sys/sys Message-ID: <20150303172745.GO32329@funkthat.com> In-Reply-To: <54F57CC6.9050109@freebsd.org> References: <201503022005.t22K5HTL062907@svn.freebsd.org> <CACYV=-FXuxzTqx12odFSRE98ydMd_AtK2GxKzv7bvLBbkAyr0A@mail.gmail.com> <CAFgRE9HR_BwWfyLVoDY0kS8rXK5p=zE0vgeCY5Ffk65ikAr2zg@mail.gmail.com> <54F57CC6.9050109@freebsd.org>
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Julian Elischer wrote this message on Tue, Mar 03, 2015 at 01:20 -0800: > On 3/2/15 4:55 PM, Neel Natu wrote: > > Hi Davide, > > > > On Mon, Mar 2, 2015 at 12:26 PM, Davide Italiano <davide@freebsd.org> wrote: > >> On Mon, Mar 2, 2015 at 12:05 PM, John-Mark Gurney <jmg@freebsd.org> wrote: > >>> Author: jmg > >>> Date: Mon Mar 2 20:05:16 2015 > >>> New Revision: 279539 > >>> URL: https://svnweb.freebsd.org/changeset/base/279539 > >>> > >>> Log: > >>> give others fair warning that _SPARE2 isn't just cxgb, but used by large > >>> number of other subsystems, so you probably don't want _SPARE2.. > >>> > >>> ktr needs an overhaul to really only compile in the ones you want, > >>> we've long passed the 31 bits it provides.. > >>> > >> If you really want to do the overhaul (which would be honestly great), > >> I might consider revamping my work for per-cpu KTR buffer and include > >> that in the change. Originally it was just an exercise, but then it > >> evolved and I've been sitting with it in my local tree for a while. I > >> never had the chutzpah to upstream it because it involves fundamental > >> changes and breaks compatibility with the old ktrdump(1) format. > >> A rather outdated (and maybe not completely functional) version of the > >> patch can be found here: > >> http://people.freebsd.org/~davide/locking/ktr_percpu.4.diff , which > >> should give you an high level view of the change. > >> I can update it to the last version and bring up for review, if > >> somebody think it might be a sane idea avoiding synchronization on a > >> single buffer for KTR. > I think it would be a problem... > one of the truely useful things about ktr is that it does use a single > buffer. > this means that you get the true interaction between CPUS. > Schedgraph relies on this (as one example). Don't some systems provide a syncronized P-state invariant TSC? If so, we can use the TSC clock to tell ordering between cores.. I could definately seeing it be a tunable that lets people force either single buffer, or PCPU buffer KTR... Where we know TSC is syncronized, we default to PCPU and others a single buffer... -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."
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