[nanomsg] Re: nn_recv with padding
- From: Martin Sustrik <sustrik@xxxxxxxxxx>
- To: Garrett D'Amore <garrett@xxxxxxxxxx>, nanomsg@xxxxxxxxxxxxx
- Date: Tue, 13 May 2014 07:18:24 +0200
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On 13/05/14 07:23, Garrett D'Amore wrote:
> Are people using such large (>100kB) messages with nanomsg? I’ve
> always assumed that zero copy was a false savings but maybe because
> I figure that the largest useful message I’d ever want send is at
> most a few pages (10k or so).
Yes, there are users with large messages. Once you get to the
megabytes range, zero-copy can actually make a difference. Now I
recall we've measured that once:
Here's the relevant table with message sizes (A), latency with copying
(B) and latency without copying (C):
(A) (B) (C)
4 kB 45.856 us 45.471 us
8 kB 55.690 us 57.462 us
16 kB 81.309 us 79.635 us
32 kB 99.423 us 97.009 us
64 kB 164.521 us 152.227 us
128 kB 227.577 us 192.544 us
256 kB 371.325 us 307.026 us
512 kB 682.949 us 528.641 us
1 MB 1464.738 us 1125.205 us
2 MB 2697.648 us 2085.429 us
4 MB 5045.856 us 3714.495 us
8 MB 9662.857 us 7199.121 us
16 MB 20898.646 us 13861.691 us
32 MB 44297.914 us 27565.414 us
64 MB 87754.242 us 54715.375 us
128 MB 167838.859 us 108787.906 us
256 MB 327360.406 us 216642.000 us
> That said, mangos has an optimization where the header space is
> allocated in such a way that attempts to avoid having to realloc or
> move a message when we want to add additional header content. But
> I’m using go byte slices for it. Sadly, go doesn’t have a nice way
> for me to preallocate “headroom” like we do with NIC packet buffers
> in the kernel.
Time to patch go? :)
Martin
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