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

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Message-ID: <0501c779-1443-702c-af7f-258e1cb05d17@gmail.com>
Date:   Mon, 7 Jan 2019 13:06:14 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Ahern <dsahern@...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 01/07/2019 12:58 PM, David Ahern wrote:
> 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.
> 

I see, maybe split this in two patches to avoid the confusion.

Why is the RTNETLINK approach better than ioctl() ?

If this is the case, maybe if_nametoindex() should be fixed, instead of carrying this locally in iproute2.