Re: [9front] Speeding up snoopy(8)

["David Arroyo" <droyo@aqwari.net>]

On Tue, Oct 18, 2022, at 00:57, droyo@aqwari.net wrote:
> 	total: 1150
> 	TEXT 00200000
> 	    ms      %   sym
> 	   360	 31.3	pread
> 	   230	 20.0	pwrite
> 	   120	 10.4	nsec
> 	   110	  9.5	_filterpkt
> 	    70	  6.0	tracepkt
> 	    60	  5.2	p_filter
> 	    60	  5.2	defaultframer
> 	    50	  4.3	p_filter
> 	    40	  3.4	be2vlong
> 	    20	  1.7	read
> 	    10	  0.8	write
> 	    10	  0.8	newfilter
> 	    10	  0.8	main
> ... snip ...
> More generally, though, I think snoopy could be much faster if it
> read multiple frames per pread() and wrote multiple records per
> pwrite(). 

I thought about this some more, and I realize that this approach is
premature at best and plain wrong at worst. Snoopy should spend as
much time as possible in pread, because that is when it is
depleting the queue. I should be trying to reduce the time spent
in everything *except* read, and only then should I be worrying
about the per-packet pread overhead.

Reading multiple packets at a time would, however, reduce the number
of nsec() calls.

I will experiment with putting the pwrite in a separate thread, and
look for small performance improvements in the other functions. I
am not sure why nsec() time is so high, but I think that's a function
that could perform very differently on real vs virtual hardware, so
I'm hesitant to try to improve it until I get 9front running on a
real machine.

David