linux-kernel - Re: Monitoring file descriptors without switching context

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Message-ID: <a57051ba1001110351sd288fk518d6dd9a58c8724@mail.gmail.com>
Date:	Mon, 11 Jan 2010 12:51:14 +0100
From:	Erik Rigtorp <erik@...torp.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Monitoring file descriptors without switching context

On Mon, Jan 11, 2010 at 11:59, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
>> What I really need is some way to have the hardware block and monitor
>> IO for me. Would it be feasible to implement a special low latency
>> poll() syscall that uses MONITOR/MWAIT instructions to monitor file
>> descriptors?
>
> The futex locks are probably the lowest level interface you've got for
> interlocking between tasks and are very fast. You can also pin tasks to
> groups of cpus so you can create an I/O only core for example.
>

For core to core signaling the fastest way is to use a memory polling
loop. Cache control instructions allows me to make sure I use L3 for
intra-cpu communication. The problem is that I also need to monitor
file descriptors and if I can make them fast enough that would be
preferable because I'm also signaled when they close.

Erik
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