Date: Thu, 20 Feb 2014 01:44:28 +0400 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: Alexander Motin <mav@FreeBSD.org> Cc: Adrian Chadd <adrian@freebsd.org>, freebsd-current <freebsd-current@freebsd.org>, Jeffrey Faden <jeffreyatw@gmail.com>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: [rfc] bind per-cpu timeout threads to each CPU Message-ID: <20140219214428.GA53864@zxy.spb.ru> In-Reply-To: <53051C71.3050705@FreeBSD.org> References: <530508B7.7060102@FreeBSD.org> <CAJ-VmokQ_C=YVpk41_r-QakB46_RWRe0didq1_RrZBMS7hDX-A@mail.gmail.com> <53050D24.3020505@FreeBSD.org> <CAJ-Vmo=KFF_2tdyq1u=jNkWfEe1sR-89t3JNggf7MEvYsF%2BtQg@mail.gmail.com> <53051C71.3050705@FreeBSD.org>
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On Wed, Feb 19, 2014 at 11:04:49PM +0200, Alexander Motin wrote: > On 19.02.2014 22:04, Adrian Chadd wrote: > > On 19 February 2014 11:59, Alexander Motin <mav@freebsd.org> wrote: > > > >>> So if we're moving towards supporting (among others) a pcbgroup / RSS > >>> hash style work load distribution across CPUs to minimise > >>> per-connection lock contention, we really don't want the scheduler to > >>> decide it can schedule things on other CPUs under enough pressure. > >>> That'll just make things worse. > > > >> True, though it is also not obvious that putting second thread on CPU run > >> queue is better then executing it right now on another core. > > > > Well, it depends if you're trying to optimise for "run all runnable > > tasks as quickly as possible" or "run all runnable tasks in contexts > > that minimise lock contention." > > > > The former sounds great as long as there's no real lock contention > > going on. But as you add more chances for contention (something like > > "100,000 concurrent TCP flows") then you may end up having your TCP > > timer firing stuff interfere with more TXing or RXing on the same > > connection. > > 100K TCP flows probably means 100K locks. That means that chance of lock > collision on each of them is effectively zero. More realistic it could What about 100K/N_cpu*PPS timer's queue locks for remove/insert TCP timeouts callbacks?
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