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List:       wireguard
Subject:    Re: Allowing space for packet headers in Wintun Tx/Rx
From:       "Jason A. Donenfeld" <Jason () zx2c4 ! com>
Date:       2021-04-13 22:09:01
Message-ID: CAHmME9pupX_RtsfNEA0N4bSG44rQNzGYyt4cDWXMK495Bu43Dw () mail ! gmail ! com
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On Mon, Apr 12, 2021 at 11:03 AM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> Sorry I'm a bit late to this thread. I'm happy to see there's a
> prototype for benchmarking, though I do wonder if this is a bit of
> overeager optimization? That is, why is this necessary and does it
> actually help?
>
> By returning packets back to the Wintun ring later, more of the ring
> winds up being used, which in turn means more cache misses as it spans
> additional cache lines. In other words, it seems like this might be
> comparing the performance of memcpy+cache no-memcpy+cachemiss. Which
> is better, and is it actually measurable? Is it possible that adding
> this functionality actually has zero measurable impact on performance?
> Given the complexity this adds, it'd be nice to see some numbers to
> help make the argument, or perhaps reasoning that's more sophisticated
> than my own napkin thoughts here.

I've moved these improvements to this branch while we wait for
additional argumentation:
https://git.zx2c4.com/wintun/log/?h=sr/api-improvements
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