netdev - Re: SSE instructions for fast packet copy?

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Message-ID: <20170508194621.5khsjn7xgdxfggfz@f1.synalogic.ca>
Date:   Mon, 8 May 2017 15:46:21 -0400
From:   Benjamin Poirier <benjamin.poirier@...il.com>
To:     Tom Herbert <tom@...bertland.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: SSE instructions for fast packet copy?

On 2017/05/04 22:50, Tom Herbert wrote:
> Hi,
> 
> I am thinking about the possibility of using SSE in kernel for
> speeding up the kernel memcpy particularly for copy to userspace
> emeory, and maybe even using the string instructions (like if we
> supported regex in something like eBPF). AFAIK we don't use SSE in
> kernel because of xmm register state needing to be saved across
> context switch. However, if we start busy-polling a CPU in kernel on
> network queues then there might not be any context switches to worry
> about. In this model we'd want to enable SSE per CPU.
> 
> Has this ever been tried before? Is this at all feasible? :-) Is it
> possible to enable SSE for kernel for just one CPU? (I found CPUID
> will return SSE supported, but don't see how to enable other than
> -msse for compiling).

This reminds me of what you tried in
	c6e1a0d12ca7 net: Allow no-cache copy from user on transmit
	(v3.0-rc1)
and that I reverted in
	cdb3f4a31b64 net: Do not enable tx-nocache-copy by default
	(v3.14-rc1)

Sure, it's not exactly the same thing...