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Date:      Wed, 25 Feb 2015 09:11:05 -0500
From:      Alfred Perlstein <bright@mu.org>
To:        Konstantin Belousov <kostikbel@gmail.com>,  Harrison Grundy <harrison.grundy@astrodoggroup.com>
Cc:        freebsd-arch@freebsd.org
Subject:   Re: locks and kernel randomness...
Message-ID:  <54EDD7F9.9030608@mu.org>
In-Reply-To: <20150225085659.GA74514@kib.kiev.ua>
References:  <DD06E2EA-68D6-43D7-AA17-FB230750E55A@bsdimp.com> <20150224174053.GG46794@funkthat.com> <54ECBD4B.6000007@freebsd.org> <20150224182507.GI46794@funkthat.com> <54ECEA43.2080008@freebsd.org> <20150224231921.GQ46794@funkthat.com> <CAHM0Q_NhUpr_HJZZcAEoZ_hNvZKcVzUBH-7LALsbkgqjLimA7A@mail.gmail.com> <20150225002301.GS46794@funkthat.com> <54ED80BD.1080603@freebsd.org> <54ED87E9.8030706@astrodoggroup.com> <20150225085659.GA74514@kib.kiev.ua>

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On 2/25/15 3:56 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.
>

Thank you.

-Alfred



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