netdev - Re: [PATCH iproute2-next] Improve batch times by caching link lookups

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Message-ID: <89099221-ca87-3298-47bf-b8e68403c2b2@gmail.com>
Date:   Mon, 7 Jan 2019 13:58:31 -0700
From:   David Ahern <dsahern@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        David Ahern <dsahern@...nel.org>, stephen@...workplumber.org
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH iproute2-next] Improve batch times by caching link lookups

On 1/7/19 1:57 PM, Eric Dumazet wrote:
> 
> 
> On 01/07/2019 12:41 PM, David Ahern wrote:
>> From: David Ahern <dsahern@...il.com>
>>
>> ip route uses ll_name_to_index to convert the user given device name to an
>> index. At the moment ll_name_to_index uses if_nametoindex which is ioctl
>> based and does not cache the result. When using a batch file this means
>> the same device lookups can be done repeatedly adding unnecessary overhead
>> (socket + ioctl call for each device lookup).
>>
>> Add a new function, ll_link_get, to send a netlink based RTM_GETLINK. If
>> successful, cache the result in idx_head and name_head so future lookups
>> can re-use the entry.
>>
>> With this change the time to install routes via a batch file is reduced
>> from 30.7 seconds to 17.6 seconds (720,022 routes with 2 ecmp nexthops
>> where the nexthop device is given).
>>
> 
> What time increase if we have 10,000 devices, and install one route ?
> 
> Caching 10,000 devices would be quite a waste.
> 

It only lookups up the device if ll_name_to_index is invoked for the
device.

This is NOT a link dump and cache; it only adds lookups to the cache.