linux-kernel - Re: NFS: 82ms wakeup latency 4.14-rc4

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Message-ID: <1513622090.7113.66.camel@gmx.de>
Date:   Mon, 18 Dec 2017 19:34:50 +0100
From:   Mike Galbraith <efault@....de>
To:     "J. Bruce Fields" <bfields@...ldses.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Jeff Layton <jlayton@...nel.org>, linux-nfs@...r.kernel.org
Subject: Re: NFS: 82ms wakeup latency 4.14-rc4

On Mon, 2017-12-18 at 12:27 -0500, J. Bruce Fields wrote:
> I'd forgotten about throughput/latency tradeoffs--but
> couldn't those in theory be managed by runtime configuration of the
> sceduler, or at least some smaller hammer than turning off preemption
> entirely?

A kernel that has all of the goop required to support preemption can't
possibly perform as well as a kernel that can simply assume everything
is safe.  All that infrastructure costs cycles.

	-Mike