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Date: Wed, 19 Dec 2012 06:44:13 -0800
From: Matthew Jacob <mjacob@freebsd.org>
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Subject: Re: Unmapped I/O
References: <20121219135451.GU71906@kib.kiev.ua>
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On 12/19/2012 5:54 AM, Konstantin Belousov wrote:
> One of the known FreeBSD I/O path performance bootleneck is the
> neccessity to map each I/O buffer pages into KVA.  The problem is that
> on the multi-core machines, the mapping must flush TLB on all cores,
> due to the global mapping of the buffer pages into the kernel.  This
> means that buffer creation and destruction disrupts execution of all
> other cores to perform TLB shootdown through IPI, and the thread
> initiating the shootdown must wait for all other cores to execute and
> report.
>
About time!