linux-kernel - Re: Network slowdown due to CFS

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Message-ID: <20071002060848.GB18588@elte.hu>
Date:	Tue, 2 Oct 2007 08:08:48 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	David Schwartz <davids@...master.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Network slowdown due to CFS


* David Schwartz <davids@...master.com> wrote:

> > (user-space spinlocks are broken beyond words for anything but 
> > perhaps SCHED_FIFO tasks.)
> 
> User-space spinlocks are broken so spinlocks can only be implemented 
> in kernel-space? Even if you use the kernel to schedule/unschedule the 
> tasks, you still have to spin in user-space.

user-space spinlocks (in anything but SCHED_FIFO tasks) are pretty 
broken because they waste CPU time. (not as broken as yield, because 
"wasting CPU time" is a more deterministic act, but still broken) Could 
you cite a single example where user-space spinlocks are technically the 
best solution?

	Ingo
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