linux-kernel - Re: [PATCH] Prevent users from disabling tickless

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Message-ID: <AANLkTikJu1saccQ6XB3KwCw-1XMR0+j5aDwp_HNFYpf2@mail.gmail.com>
Date:	Sun, 2 Jan 2011 12:06:28 +0100
From:	Remy Bohmer <linux@...mer.net>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Prevent users from disabling tickless

Hi,

2010/12/22 Matthew Wilcox <matthew@....cx>:
>
> Disabling NO_HZ has a serious negative effect on performance -- an extra
> 70us per I/O.  Prevent users from deselecting it.

Enabling NO_HZ has a serious negative effect on realtime due to longer
interrupt handling and less predictability of the system.
We prefer to align the timer interrupt handling to the interrupt
handling of our realtime control loops so they do not bother each
other. A varying moment of the timer interrupt handling would destroy
much realtime responsiveness here.

So, what is good for throughput is usually bad for responsiveness...

This is an example that the many different applications of the Linux
kernel demand a different configuration of the kernel.
I prefer to keep it configurable.

Kind regards,

Remy
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