netdev - Re: [PATCH v3] net: use exponential backoff in netdev_wait

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Message-ID: <20200917170203.1a363082@hermes.lan>
Date:   Thu, 17 Sep 2020 17:02:03 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     fruggeri@...sta.com (Francesco Ruggeri)
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        xiyou.wangcong@...il.com, ap420073@...il.com, andriin@...com,
        edumazet@...gle.com, jiri@...lanox.com, ast@...nel.org,
        kuba@...nel.org, davem@...emloft.net
Subject: Re: [PATCH v3] net: use exponential backoff in netdev_wait_allrefs

On Thu, 17 Sep 2020 16:49:53 -0700
fruggeri@...sta.com (Francesco Ruggeri) wrote:

> The combination of aca_free_rcu, introduced in commit 2384d02520ff
> ("net/ipv6: Add anycast addresses to a global hashtable"), and
> fib6_info_destroy_rcu, introduced in commit 9b0a8da8c4c6 ("net/ipv6:
> respect rcu grace period before freeing fib6_info"), can result in
> an extra rcu grace period being needed when deleting an interface,
> with the result that netdev_wait_allrefs ends up hitting the msleep(250),
> which is considerably longer than the required grace period.
> This can result in long delays when deleting a large number of interfaces,
> and it can be observed with this script:
> 

Is there anyway to make RCU trigger faster?