netdev - Re: [PATCH net-next] ipv6: only update __use and lastusetime once per jiffy at most

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Date:   Fri, 13 Oct 2017 17:09:24 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Wei Wang <weiwan@...gle.com>
CC:     David Miller <davem@...emloft.net>, <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next] ipv6: only update __use and lastusetime once
 per jiffy at most

On Fri, Oct 13, 2017 at 10:08:07PM +0000, Wei Wang wrote:
> From: Wei Wang <weiwan@...gle.com>
> 
> In order to not dirty the cacheline too often, we try to only update
> dst->__use and dst->lastusetime at most once per jiffy.


> As dst->lastusetime is only used by ipv6 garbage collector, it should
> be good enough time resolution.
Make sense.

> And __use is only used in ipv6_route_seq_show() to show how many times a
> dst has been used. And as __use is not atomic_t right now, it does not
> show the precise number of usage times anyway. So we think it should be
> OK to only update it at most once per jiffy.
If __use is only bumped HZ number of times per second and we can do ~3Mpps now,
would __use be way off?